Merge branch 'master' of /home/davem/src/GIT/linux-2.6/

Conflicts:
	drivers/net/wimax/i2400m/usb-notif.c

4 files changed, 6352 insertions, 5 deletions

diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
index 1462ed86d40a..a3a83d38f96f 100644
--- a/Documentation/DocBook/Makefile
+++ b/Documentation/DocBook/Makefile
@@ -12,7 +12,8 @@ DOCBOOKS := z8530book.xml mcabook.xml device-drivers.xml \
 	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
 	    gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
 	    genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
-	    mac80211.xml debugobjects.xml sh.xml regulator.xml
+	    mac80211.xml debugobjects.xml sh.xml regulator.xml \
+	    alsa-driver-api.xml writing-an-alsa-driver.xml
 
 ###
 # The build process is as follows (targets):
diff --git a/Documentation/DocBook/alsa-driver-api.tmpl b/Documentation/DocBook/alsa-driver-api.tmpl
new file mode 100644
index 000000000000..0230a96f0564
--- /dev/null
+++ b/Documentation/DocBook/alsa-driver-api.tmpl
@@ -0,0 +1,109 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<!-- ****************************************************** -->
+<!-- Header  -->
+<!-- ****************************************************** -->
+<book id="ALSA-Driver-API">
+  <bookinfo>
+    <title>The ALSA Driver API</title>
+
+    <legalnotice>
+    <para>
+    This document is free; you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version. 
+    </para>
+
+    <para>
+    This document is distributed in the hope that it will be useful,
+    but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the
+    implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A
+    PARTICULAR PURPOSE</emphasis>. See the GNU General Public License
+    for more details.
+    </para>
+
+    <para>
+    You should have received a copy of the GNU General Public
+    License along with this program; if not, write to the Free
+    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+    MA 02111-1307 USA
+    </para>
+    </legalnotice>
+
+  </bookinfo>
+
+<toc></toc>
+
+  <chapter><title>Management of Cards and Devices</title>
+     <sect1><title>Card Management</title>
+!Esound/core/init.c
+     </sect1>
+     <sect1><title>Device Components</title>
+!Esound/core/device.c
+     </sect1>
+     <sect1><title>Module requests and Device File Entries</title>
+!Esound/core/sound.c
+     </sect1>
+     <sect1><title>Memory Management Helpers</title>
+!Esound/core/memory.c
+!Esound/core/memalloc.c
+     </sect1>
+  </chapter>
+  <chapter><title>PCM API</title>
+     <sect1><title>PCM Core</title>
+!Esound/core/pcm.c
+!Esound/core/pcm_lib.c
+!Esound/core/pcm_native.c
+     </sect1>
+     <sect1><title>PCM Format Helpers</title>
+!Esound/core/pcm_misc.c
+     </sect1>
+     <sect1><title>PCM Memory Management</title>
+!Esound/core/pcm_memory.c
+     </sect1>
+  </chapter>
+  <chapter><title>Control/Mixer API</title>
+     <sect1><title>General Control Interface</title>
+!Esound/core/control.c
+     </sect1>
+     <sect1><title>AC97 Codec API</title>
+!Esound/pci/ac97/ac97_codec.c
+!Esound/pci/ac97/ac97_pcm.c
+     </sect1>
+     <sect1><title>Virtual Master Control API</title>
+!Esound/core/vmaster.c
+!Iinclude/sound/control.h
+     </sect1>
+  </chapter>
+  <chapter><title>MIDI API</title>
+     <sect1><title>Raw MIDI API</title>
+!Esound/core/rawmidi.c
+     </sect1>
+     <sect1><title>MPU401-UART API</title>
+!Esound/drivers/mpu401/mpu401_uart.c
+     </sect1>
+  </chapter>
+  <chapter><title>Proc Info API</title>
+     <sect1><title>Proc Info Interface</title>
+!Esound/core/info.c
+     </sect1>
+  </chapter>
+  <chapter><title>Miscellaneous Functions</title>
+     <sect1><title>Hardware-Dependent Devices API</title>
+!Esound/core/hwdep.c
+     </sect1>
+     <sect1><title>Jack Abstraction Layer API</title>
+!Esound/core/jack.c
+     </sect1>
+     <sect1><title>ISA DMA Helpers</title>
+!Esound/core/isadma.c
+     </sect1>
+     <sect1><title>Other Helper Macros</title>
+!Iinclude/sound/core.h
+     </sect1>
+  </chapter>
+
+</book>
diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index 52e1b79ce0e6..8f6e3b2403c7 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -42,6 +42,13 @@ GPL version 2.
 
 <revhistory>
 	<revision>
+	<revnumber>0.8</revnumber>
+	<date>2008-12-24</date>
+	<authorinitials>hjk</authorinitials>
+	<revremark>Added name attributes in mem and portio sysfs directories.
+		</revremark>
+	</revision>
+	<revision>
 	<revnumber>0.7</revnumber>
 	<date>2008-12-23</date>
 	<authorinitials>hjk</authorinitials>
@@ -303,12 +310,19 @@ interested in translating it, please email me
 	appear if the size of the mapping is not 0.
 </para>
 <para>
-	Each <filename>mapX/</filename> directory contains two read-only files
-	that show start address and size of the memory:
+	Each <filename>mapX/</filename> directory contains four read-only files
+	that show attributes of the memory:
 </para>
 <itemizedlist>
 <listitem>
 	<para>
+	<filename>name</filename>: A string identifier for this mapping. This
+	is optional, the string can be empty. Drivers can set this to make it
+	easier for userspace to find the correct mapping.
+	</para>
+</listitem>
+<listitem>
+	<para>
 	<filename>addr</filename>: The address of memory that can be mapped.
 	</para>
 </listitem>
@@ -366,12 +380,19 @@ offset = N * getpagesize();
 	<filename>/sys/class/uio/uioX/portio/</filename>.
 </para>
 <para>
-	Each <filename>portX/</filename> directory contains three read-only
-	files that show start, size, and type of the port region:
+	Each <filename>portX/</filename> directory contains four read-only
+	files that show name, start, size, and type of the port region:
 </para>
 <itemizedlist>
 <listitem>
 	<para>
+	<filename>name</filename>: A string identifier for this port region.
+	The string is optional and can be empty. Drivers can set it to make it
+	easier for userspace to find a certain port region.
+	</para>
+</listitem>
+<listitem>
+	<para>
 	<filename>start</filename>: The first port of this region.
 	</para>
 </listitem>
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl
new file mode 100644
index 000000000000..46b08fef3744
--- /dev/null
+++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl
@@ -0,0 +1,6216 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<!-- ****************************************************** -->
+<!-- Header  -->
+<!-- ****************************************************** -->
+<book id="Writing-an-ALSA-Driver">
+  <bookinfo>
+    <title>Writing an ALSA Driver</title>
+    <author>
+      <firstname>Takashi</firstname>
+      <surname>Iwai</surname>
+      <affiliation>
+        <address>
+          <email>tiwai@suse.de</email>
+        </address>
+      </affiliation>
+     </author>
+
+     <date>Oct 15, 2007</date>
+     <edition>0.3.7</edition>
+
+    <abstract>
+      <para>
+        This document describes how to write an ALSA (Advanced Linux
+        Sound Architecture) driver.
+      </para>
+    </abstract>
+
+    <legalnotice>
+    <para>
+    Copyright (c) 2002-2005  Takashi Iwai <email>tiwai@suse.de</email>
+    </para>
+
+    <para>
+    This document is free; you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version. 
+    </para>
+
+    <para>
+    This document is distributed in the hope that it will be useful,
+    but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the
+    implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A
+    PARTICULAR PURPOSE</emphasis>. See the GNU General Public License
+    for more details.
+    </para>
+
+    <para>
+    You should have received a copy of the GNU General Public
+    License along with this program; if not, write to the Free
+    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+    MA 02111-1307 USA
+    </para>
+    </legalnotice>
+
+  </bookinfo>
+
+<!-- ****************************************************** -->
+<!-- Preface  -->
+<!-- ****************************************************** -->
+  <preface id="preface">
+    <title>Preface</title>
+    <para>
+      This document describes how to write an
+      <ulink url="http://www.alsa-project.org/"><citetitle>
+      ALSA (Advanced Linux Sound Architecture)</citetitle></ulink>
+      driver. The document focuses mainly on PCI soundcards.
+      In the case of other device types, the API might
+      be different, too. However, at least the ALSA kernel API is
+      consistent, and therefore it would be still a bit help for
+      writing them.
+    </para>
+
+    <para>
+    This document targets people who already have enough
+    C language skills and have basic linux kernel programming
+    knowledge.  This document doesn't explain the general
+    topic of linux kernel coding and doesn't cover low-level
+    driver implementation details. It only describes
+    the standard way to write a PCI sound driver on ALSA.
+    </para>
+
+    <para>
+      If you are already familiar with the older ALSA ver.0.5.x API, you
+    can check the drivers such as <filename>sound/pci/es1938.c</filename> or
+    <filename>sound/pci/maestro3.c</filename> which have also almost the same
+    code-base in the ALSA 0.5.x tree, so you can compare the differences.
+    </para>
+
+    <para>
+      This document is still a draft version. Any feedback and
+    corrections, please!!
+    </para>
+  </preface>
+
+
+<!-- ****************************************************** -->
+<!-- File Tree Structure  -->
+<!-- ****************************************************** -->
+  <chapter id="file-tree">
+    <title>File Tree Structure</title>
+
+    <section id="file-tree-general">
+      <title>General</title>
+      <para>
+        The ALSA drivers are provided in two ways.
+      </para>
+
+      <para>
+        One is the trees provided as a tarball or via cvs from the
+      ALSA's ftp site, and another is the 2.6 (or later) Linux kernel
+      tree. To synchronize both, the ALSA driver tree is split into
+      two different trees: alsa-kernel and alsa-driver. The former
+      contains purely the source code for the Linux 2.6 (or later)
+      tree. This tree is designed only for compilation on 2.6 or
+      later environment. The latter, alsa-driver, contains many subtle
+      files for compiling ALSA drivers outside of the Linux kernel tree,
+      wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API,
+      and additional drivers which are still in development or in
+      tests.  The drivers in alsa-driver tree will be moved to
+      alsa-kernel (and eventually to the 2.6 kernel tree) when they are
+      finished and confirmed to work fine.
+      </para>
+
+      <para>
+        The file tree structure of ALSA driver is depicted below. Both
+        alsa-kernel and alsa-driver have almost the same file
+        structure, except for <quote>core</quote> directory. It's
+        named as <quote>acore</quote> in alsa-driver tree. 
+
+        <example>
+          <title>ALSA File Tree Structure</title>
+          <literallayout>
+        sound
+                /core
+                        /oss
+                        /seq
+                                /oss
+                                /instr
+                /ioctl32
+                /include
+                /drivers
+                        /mpu401
+                        /opl3
+                /i2c
+                        /l3
+                /synth
+                        /emux
+                /pci
+                        /(cards)
+                /isa
+                        /(cards)
+                /arm
+                /ppc
+                /sparc
+                /usb
+                /pcmcia /(cards)
+                /oss
+          </literallayout>
+        </example>
+      </para>
+    </section>
+
+    <section id="file-tree-core-directory">
+      <title>core directory</title>
+      <para>
+        This directory contains the middle layer which is the heart
+      of ALSA drivers. In this directory, the native ALSA modules are
+      stored. The sub-directories contain different modules and are
+      dependent upon the kernel config. 
+      </para>
+
+      <section id="file-tree-core-directory-oss">
+        <title>core/oss</title>
+
+        <para>
+          The codes for PCM and mixer OSS emulation modules are stored
+        in this directory. The rawmidi OSS emulation is included in
+        the ALSA rawmidi code since it's quite small. The sequencer
+        code is stored in <filename>core/seq/oss</filename> directory (see
+        <link linkend="file-tree-core-directory-seq-oss"><citetitle>
+        below</citetitle></link>).
+        </para>
+      </section>
+
+      <section id="file-tree-core-directory-ioctl32">
+        <title>core/ioctl32</title>
+
+        <para>
+          This directory contains the 32bit-ioctl wrappers for 64bit
+        architectures such like x86-64, ppc64 and sparc64. For 32bit
+        and alpha architectures, these are not compiled. 
+        </para>
+      </section>
+
+      <section id="file-tree-core-directory-seq">
+        <title>core/seq</title>
+        <para>
+          This directory and its sub-directories are for the ALSA
+        sequencer. This directory contains the sequencer core and
+        primary sequencer modules such like snd-seq-midi,
+        snd-seq-virmidi, etc. They are compiled only when
+        <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel
+        config. 
+        </para>
+      </section>
+
+      <section id="file-tree-core-directory-seq-oss">
+        <title>core/seq/oss</title>
+        <para>
+          This contains the OSS sequencer emulation codes.
+        </para>
+      </section>
+
+      <section id="file-tree-core-directory-deq-instr">
+        <title>core/seq/instr</title>
+        <para>
+          This directory contains the modules for the sequencer
+        instrument layer. 
+        </para>
+      </section>
+    </section>
+
+    <section id="file-tree-include-directory">
+      <title>include directory</title>
+      <para>
+        This is the place for the public header files of ALSA drivers,
+      which are to be exported to user-space, or included by
+      several files at different directories. Basically, the private
+      header files should not be placed in this directory, but you may
+      still find files there, due to historical reasons :) 
+      </para>
+    </section>
+
+    <section id="file-tree-drivers-directory">
+      <title>drivers directory</title>
+      <para>
+        This directory contains code shared among different drivers
+      on different architectures.  They are hence supposed not to be
+      architecture-specific.
+      For example, the dummy pcm driver and the serial MIDI
+      driver are found in this directory. In the sub-directories,
+      there is code for components which are independent from
+      bus and cpu architectures. 
+      </para>
+
+      <section id="file-tree-drivers-directory-mpu401">
+        <title>drivers/mpu401</title>
+        <para>
+          The MPU401 and MPU401-UART modules are stored here.
+        </para>
+      </section>
+
+      <section id="file-tree-drivers-directory-opl3">
+        <title>drivers/opl3 and opl4</title>
+        <para>
+          The OPL3 and OPL4 FM-synth stuff is found here.
+        </para>
+      </section>
+    </section>
+
+    <section id="file-tree-i2c-directory">
+      <title>i2c directory</title>
+      <para>
+        This contains the ALSA i2c components.
+      </para>
+
+      <para>
+        Although there is a standard i2c layer on Linux, ALSA has its
+      own i2c code for some cards, because the soundcard needs only a
+      simple operation and the standard i2c API is too complicated for
+      such a purpose. 
+      </para>
+
+      <section id="file-tree-i2c-directory-l3">
+        <title>i2c/l3</title>
+        <para>
+          This is a sub-directory for ARM L3 i2c.
+        </para>
+      </section>
+    </section>
+
+    <section id="file-tree-synth-directory">
+        <title>synth directory</title>
+        <para>
+          This contains the synth middle-level modules.
+        </para>
+
+        <para>
+          So far, there is only Emu8000/Emu10k1 synth driver under
+        the <filename>synth/emux</filename> sub-directory. 
+        </para>
+    </section>
+
+    <section id="file-tree-pci-directory">
+      <title>pci directory</title>
+      <para>
+        This directory and its sub-directories hold the top-level card modules
+      for PCI soundcards and the code specific to the PCI BUS.
+      </para>
+
+      <para>
+        The drivers compiled from a single file are stored directly
+      in the pci directory, while the drivers with several source files are
+      stored on their own sub-directory (e.g. emu10k1, ice1712). 
+      </para>
+    </section>
+
+    <section id="file-tree-isa-directory">
+      <title>isa directory</title>
+      <para>
+        This directory and its sub-directories hold the top-level card modules
+      for ISA soundcards. 
+      </para>
+    </section>
+
+    <section id="file-tree-arm-ppc-sparc-directories">
+      <title>arm, ppc, and sparc directories</title>
+      <para>
+        They are used for top-level card modules which are
+      specific to one of these architectures. 
+      </para>
+    </section>
+
+    <section id="file-tree-usb-directory">
+      <title>usb directory</title>
+      <para>
+        This directory contains the USB-audio driver. In the latest version, the
+      USB MIDI driver is integrated in the usb-audio driver. 
+      </para>
+    </section>
+
+    <section id="file-tree-pcmcia-directory">
+      <title>pcmcia directory</title>
+      <para>
+        The PCMCIA, especially PCCard drivers will go here. CardBus
+      drivers will be in the pci directory, because their API is identical
+      to that of standard PCI cards. 
+      </para>
+    </section>
+
+    <section id="file-tree-oss-directory">
+      <title>oss directory</title>
+      <para>
+        The OSS/Lite source files are stored here in Linux 2.6 (or
+      later) tree. In the ALSA driver tarball, this directory is empty,
+      of course :) 
+      </para>
+    </section>
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Basic Flow for PCI Drivers  -->
+<!-- ****************************************************** -->
+  <chapter id="basic-flow">
+    <title>Basic Flow for PCI Drivers</title>
+
+    <section id="basic-flow-outline">
+      <title>Outline</title>
+      <para>
+        The minimum flow for PCI soundcards is as follows:
+
+        <itemizedlist>
+          <listitem><para>define the PCI ID table (see the section
+          <link linkend="pci-resource-entries"><citetitle>PCI Entries
+          </citetitle></link>).</para></listitem> 
+          <listitem><para>create <function>probe()</function> callback.</para></listitem>
+          <listitem><para>create <function>remove()</function> callback.</para></listitem>
+          <listitem><para>create a <structname>pci_driver</structname> structure
+	  containing the three pointers above.</para></listitem>
+          <listitem><para>create an <function>init()</function> function just calling
+	  the <function>pci_register_driver()</function> to register the pci_driver table
+	  defined above.</para></listitem>
+          <listitem><para>create an <function>exit()</function> function to call
+	  the <function>pci_unregister_driver()</function> function.</para></listitem>
+        </itemizedlist>
+      </para>
+    </section>
+
+    <section id="basic-flow-example">
+      <title>Full Code Example</title>
+      <para>
+        The code example is shown below. Some parts are kept
+      unimplemented at this moment but will be filled in the
+      next sections. The numbers in the comment lines of the
+      <function>snd_mychip_probe()</function> function
+      refer to details explained in the following section. 
+
+        <example>
+          <title>Basic Flow for PCI Drivers - Example</title>
+          <programlisting>
+<![CDATA[
+  #include <linux/init.h>
+  #include <linux/pci.h>
+  #include <linux/slab.h>
+  #include <sound/core.h>
+  #include <sound/initval.h>
+
+  /* module parameters (see "Module Parameters") */
+  /* SNDRV_CARDS: maximum number of cards supported by this module */
+  static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
+  static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
+  static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
+
+  /* definition of the chip-specific record */
+  struct mychip {
+          struct snd_card *card;
+          /* the rest of the implementation will be in section
+           * "PCI Resource Management"
+           */
+  };
+
+  /* chip-specific destructor
+   * (see "PCI Resource Management")
+   */
+  static int snd_mychip_free(struct mychip *chip)
+  {
+          .... /* will be implemented later... */
+  }
+
+  /* component-destructor
+   * (see "Management of Cards and Components")
+   */
+  static int snd_mychip_dev_free(struct snd_device *device)
+  {
+          return snd_mychip_free(device->device_data);
+  }
+
+  /* chip-specific constructor
+   * (see "Management of Cards and Components")
+   */
+  static int __devinit snd_mychip_create(struct snd_card *card,
+                                         struct pci_dev *pci,
+                                         struct mychip **rchip)
+  {
+          struct mychip *chip;
+          int err;
+          static struct snd_device_ops ops = {
+                 .dev_free = snd_mychip_dev_free,
+          };
+
+          *rchip = NULL;
+
+          /* check PCI availability here
+           * (see "PCI Resource Management")
+           */
+          ....
+
+          /* allocate a chip-specific data with zero filled */
+          chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+          if (chip == NULL)
+                  return -ENOMEM;
+
+          chip->card = card;
+
+          /* rest of initialization here; will be implemented
+           * later, see "PCI Resource Management"
+           */
+          ....
+
+          err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+          if (err < 0) {
+                  snd_mychip_free(chip);
+                  return err;
+          }
+
+          snd_card_set_dev(card, &pci->dev);
+
+          *rchip = chip;
+          return 0;
+  }
+
+  /* constructor -- see "Constructor" sub-section */
+  static int __devinit snd_mychip_probe(struct pci_dev *pci,
+                               const struct pci_device_id *pci_id)
+  {
+          static int dev;
+          struct snd_card *card;
+          struct mychip *chip;
+          int err;
+
+          /* (1) */
+          if (dev >= SNDRV_CARDS)
+                  return -ENODEV;
+          if (!enable[dev]) {
+                  dev++;
+                  return -ENOENT;
+          }
+
+          /* (2) */
+          err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
+          if (err < 0)
+                  return err;
+
+          /* (3) */
+          err = snd_mychip_create(card, pci, &chip);
+          if (err < 0) {
+                  snd_card_free(card);
+                  return err;
+          }
+
+          /* (4) */
+          strcpy(card->driver, "My Chip");
+          strcpy(card->shortname, "My Own Chip 123");
+          sprintf(card->longname, "%s at 0x%lx irq %i",
+                  card->shortname, chip->ioport, chip->irq);
+
+          /* (5) */
+          .... /* implemented later */
+
+          /* (6) */
+          err = snd_card_register(card);
+          if (err < 0) {
+                  snd_card_free(card);
+                  return err;
+          }
+
+          /* (7) */
+          pci_set_drvdata(pci, card);
+          dev++;
+          return 0;
+  }
+
+  /* destructor -- see the "Destructor" sub-section */
+  static void __devexit snd_mychip_remove(struct pci_dev *pci)
+  {
+          snd_card_free(pci_get_drvdata(pci));
+          pci_set_drvdata(pci, NULL);
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+    </section>
+
+    <section id="basic-flow-constructor">
+      <title>Constructor</title>
+      <para>
+        The real constructor of PCI drivers is the <function>probe</function> callback.
+      The <function>probe</function> callback and other component-constructors which are called
+      from the <function>probe</function> callback should be defined with
+      the <parameter>__devinit</parameter> prefix. You 
+      cannot use the <parameter>__init</parameter> prefix for them,
+      because any PCI device could be a hotplug device. 
+      </para>
+
+      <para>
+        In the <function>probe</function> callback, the following scheme is often used.
+      </para>
+
+      <section id="basic-flow-constructor-device-index">
+        <title>1) Check and increment the device index.</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int dev;
+  ....
+  if (dev >= SNDRV_CARDS)
+          return -ENODEV;
+  if (!enable[dev]) {
+          dev++;
+          return -ENOENT;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+
+        where enable[dev] is the module option.
+        </para>
+
+        <para>
+          Each time the <function>probe</function> callback is called, check the
+        availability of the device. If not available, simply increment
+        the device index and returns. dev will be incremented also
+        later (<link
+        linkend="basic-flow-constructor-set-pci"><citetitle>step
+        7</citetitle></link>). 
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-create-card">
+        <title>2) Create a card instance</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  struct snd_card *card;
+  int err;
+  ....
+  err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          The details will be explained in the section
+          <link linkend="card-management-card-instance"><citetitle>
+          Management of Cards and Components</citetitle></link>.
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-create-main">
+        <title>3) Create a main component</title>
+        <para>
+          In this part, the PCI resources are allocated.
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  struct mychip *chip;
+  ....
+  err = snd_mychip_create(card, pci, &chip);
+  if (err < 0) {
+          snd_card_free(card);
+          return err;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+
+          The details will be explained in the section <link
+        linkend="pci-resource"><citetitle>PCI Resource
+        Management</citetitle></link>.
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-main-component">
+        <title>4) Set the driver ID and name strings.</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  strcpy(card->driver, "My Chip");
+  strcpy(card->shortname, "My Own Chip 123");
+  sprintf(card->longname, "%s at 0x%lx irq %i",
+          card->shortname, chip->ioport, chip->irq);
+]]>
+            </programlisting>
+          </informalexample>
+
+          The driver field holds the minimal ID string of the
+        chip. This is used by alsa-lib's configurator, so keep it
+        simple but unique. 
+          Even the same driver can have different driver IDs to
+        distinguish the functionality of each chip type. 
+        </para>
+
+        <para>
+          The shortname field is a string shown as more verbose
+        name. The longname field contains the information
+        shown in <filename>/proc/asound/cards</filename>. 
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-create-other">
+        <title>5) Create other components, such as mixer, MIDI, etc.</title>
+        <para>
+          Here you define the basic components such as
+          <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>,
+          mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>),
+          MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>),
+          and other interfaces.
+          Also, if you want a <link linkend="proc-interface"><citetitle>proc
+        file</citetitle></link>, define it here, too.
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-register-card">
+        <title>6) Register the card instance.</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  err = snd_card_register(card);
+  if (err < 0) {
+          snd_card_free(card);
+          return err;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          Will be explained in the section <link
+        linkend="card-management-registration"><citetitle>Management
+        of Cards and Components</citetitle></link>, too. 
+        </para>
+      </section>
+
+      <section id="basic-flow-constructor-set-pci">
+        <title>7) Set the PCI driver data and return zero.</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+        pci_set_drvdata(pci, card);
+        dev++;
+        return 0;
+]]>
+            </programlisting>
+          </informalexample>
+
+          In the above, the card record is stored. This pointer is
+        used in the remove callback and power-management
+        callbacks, too. 
+        </para>
+      </section>
+    </section>
+
+    <section id="basic-flow-destructor">
+      <title>Destructor</title>
+      <para>
+        The destructor, remove callback, simply releases the card
+      instance. Then the ALSA middle layer will release all the
+      attached components automatically. 
+      </para>
+
+      <para>
+        It would be typically like the following:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void __devexit snd_mychip_remove(struct pci_dev *pci)
+  {
+          snd_card_free(pci_get_drvdata(pci));
+          pci_set_drvdata(pci, NULL);
+  }
+]]>
+          </programlisting>
+        </informalexample>
+
+        The above code assumes that the card pointer is set to the PCI
+	driver data.
+      </para>
+    </section>
+
+    <section id="basic-flow-header-files">
+      <title>Header Files</title>
+      <para>
+        For the above example, at least the following include files
+      are necessary. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  #include <linux/init.h>
+  #include <linux/pci.h>
+  #include <linux/slab.h>
+  #include <sound/core.h>
+  #include <sound/initval.h>
+]]>
+          </programlisting>
+        </informalexample>
+
+	where the last one is necessary only when module options are
+      defined in the source file.  If the code is split into several
+      files, the files without module options don't need them.
+      </para>
+
+      <para>
+        In addition to these headers, you'll need
+      <filename>&lt;linux/interrupt.h&gt;</filename> for interrupt
+      handling, and <filename>&lt;asm/io.h&gt;</filename> for I/O
+      access. If you use the <function>mdelay()</function> or
+      <function>udelay()</function> functions, you'll need to include
+      <filename>&lt;linux/delay.h&gt;</filename> too. 
+      </para>
+
+      <para>
+      The ALSA interfaces like the PCM and control APIs are defined in other
+      <filename>&lt;sound/xxx.h&gt;</filename> header files.
+      They have to be included after
+      <filename>&lt;sound/core.h&gt;</filename>.
+      </para>
+
+    </section>
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Management of Cards and Components  -->
+<!-- ****************************************************** -->
+  <chapter id="card-management">
+    <title>Management of Cards and Components</title>
+
+    <section id="card-management-card-instance">
+      <title>Card Instance</title>
+      <para>
+      For each soundcard, a <quote>card</quote> record must be allocated.
+      </para>
+
+      <para>
+      A card record is the headquarters of the soundcard.  It manages
+      the whole list of devices (components) on the soundcard, such as
+      PCM, mixers, MIDI, synthesizer, and so on.  Also, the card
+      record holds the ID and the name strings of the card, manages
+      the root of proc files, and controls the power-management states
+      and hotplug disconnections.  The component list on the card
+      record is used to manage the correct release of resources at
+      destruction. 
+      </para>
+
+      <para>
+        As mentioned above, to create a card instance, call
+      <function>snd_card_create()</function>.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_card *card;
+  int err;
+  err = snd_card_create(index, id, module, extra_size, &card);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The function takes five arguments, the card-index number, the
+        id string, the module pointer (usually
+        <constant>THIS_MODULE</constant>),
+        the size of extra-data space, and the pointer to return the
+        card instance.  The extra_size argument is used to
+        allocate card-&gt;private_data for the
+        chip-specific data.  Note that these data
+        are allocated by <function>snd_card_create()</function>.
+      </para>
+    </section>
+
+    <section id="card-management-component">
+      <title>Components</title>
+      <para>
+        After the card is created, you can attach the components
+      (devices) to the card instance. In an ALSA driver, a component is
+      represented as a struct <structname>snd_device</structname> object.
+      A component can be a PCM instance, a control interface, a raw
+      MIDI interface, etc.  Each such instance has one component
+      entry.
+      </para>
+
+      <para>
+        A component can be created via
+        <function>snd_device_new()</function> function. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_device_new(card, SNDRV_DEV_XXX, chip, &ops);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        This takes the card pointer, the device-level
+      (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the
+      callback pointers (<parameter>&amp;ops</parameter>). The
+      device-level defines the type of components and the order of
+      registration and de-registration.  For most components, the
+      device-level is already defined.  For a user-defined component,
+      you can use <constant>SNDRV_DEV_LOWLEVEL</constant>.
+      </para>
+
+      <para>
+      This function itself doesn't allocate the data space. The data
+      must be allocated manually beforehand, and its pointer is passed
+      as the argument. This pointer is used as the
+      (<parameter>chip</parameter> identifier in the above example)
+      for the instance. 
+      </para>
+
+      <para>
+        Each pre-defined ALSA component such as ac97 and pcm calls
+      <function>snd_device_new()</function> inside its
+      constructor. The destructor for each component is defined in the
+      callback pointers.  Hence, you don't need to take care of
+      calling a destructor for such a component.
+      </para>
+
+      <para>
+        If you wish to create your own component, you need to
+      set the destructor function to the dev_free callback in
+      the <parameter>ops</parameter>, so that it can be released
+      automatically via <function>snd_card_free()</function>.
+      The next example will show an implementation of chip-specific
+      data.
+      </para>
+    </section>
+
+    <section id="card-management-chip-specific">
+      <title>Chip-Specific Data</title>
+      <para>
+      Chip-specific information, e.g. the I/O port address, its
+      resource pointer, or the irq number, is stored in the
+      chip-specific record.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct mychip {
+          ....
+  };
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        In general, there are two ways of allocating the chip record.
+      </para>
+
+      <section id="card-management-chip-specific-snd-card-new">
+        <title>1. Allocating via <function>snd_card_create()</function>.</title>
+        <para>
+          As mentioned above, you can pass the extra-data-length
+	  to the 4th argument of <function>snd_card_create()</function>, i.e.
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  err = snd_card_create(index[dev], id[dev], THIS_MODULE,
+                        sizeof(struct mychip), &card);
+]]>
+            </programlisting>
+          </informalexample>
+
+          struct <structname>mychip</structname> is the type of the chip record.
+        </para>
+
+        <para>
+          In return, the allocated record can be accessed as
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  struct mychip *chip = card->private_data;
+]]>
+            </programlisting>
+          </informalexample>
+
+          With this method, you don't have to allocate twice.
+          The record is released together with the card instance.
+        </para>
+      </section>
+
+      <section id="card-management-chip-specific-allocate-extra">
+        <title>2. Allocating an extra device.</title>
+
+        <para>
+          After allocating a card instance via
+          <function>snd_card_create()</function> (with
+          <constant>0</constant> on the 4th arg), call
+          <function>kzalloc()</function>. 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  struct snd_card *card;
+  struct mychip *chip;
+  err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
+  .....
+  chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          The chip record should have the field to hold the card
+          pointer at least, 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  struct mychip {
+          struct snd_card *card;
+          ....
+  };
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          Then, set the card pointer in the returned chip instance.
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  chip->card = card;
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          Next, initialize the fields, and register this chip
+          record as a low-level device with a specified
+          <parameter>ops</parameter>, 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static struct snd_device_ops ops = {
+          .dev_free =        snd_mychip_dev_free,
+  };
+  ....
+  snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+]]>
+            </programlisting>
+          </informalexample>
+
+          <function>snd_mychip_dev_free()</function> is the
+        device-destructor function, which will call the real
+        destructor. 
+        </para>
+
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_mychip_dev_free(struct snd_device *device)
+  {
+          return snd_mychip_free(device->device_data);
+  }
+]]>
+            </programlisting>
+          </informalexample>
+
+          where <function>snd_mychip_free()</function> is the real destructor.
+        </para>
+      </section>
+    </section>
+
+    <section id="card-management-registration">
+      <title>Registration and Release</title>
+      <para>
+        After all components are assigned, register the card instance
+      by calling <function>snd_card_register()</function>. Access
+      to the device files is enabled at this point. That is, before
+      <function>snd_card_register()</function> is called, the
+      components are safely inaccessible from external side. If this
+      call fails, exit the probe function after releasing the card via
+      <function>snd_card_free()</function>. 
+      </para>
+
+      <para>
+        For releasing the card instance, you can call simply
+      <function>snd_card_free()</function>. As mentioned earlier, all
+      components are released automatically by this call. 
+      </para>
+
+      <para>
+        As further notes, the destructors (both
+      <function>snd_mychip_dev_free</function> and
+      <function>snd_mychip_free</function>) cannot be defined with
+      the <parameter>__devexit</parameter> prefix, because they may be
+      called from the constructor, too, at the false path. 
+      </para>
+
+      <para>
+      For a device which allows hotplugging, you can use
+      <function>snd_card_free_when_closed</function>.  This one will
+      postpone the destruction until all devices are closed.
+      </para>
+
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- PCI Resource Management  -->
+<!-- ****************************************************** -->
+  <chapter id="pci-resource">
+    <title>PCI Resource Management</title>
+
+    <section id="pci-resource-example">
+      <title>Full Code Example</title>
+      <para>
+        In this section, we'll complete the chip-specific constructor,
+      destructor and PCI entries. Example code is shown first,
+      below. 
+
+        <example>
+          <title>PCI Resource Management Example</title>
+          <programlisting>
+<![CDATA[
+  struct mychip {
+          struct snd_card *card;
+          struct pci_dev *pci;
+
+          unsigned long port;
+          int irq;
+  };
+
+  static int snd_mychip_free(struct mychip *chip)
+  {
+          /* disable hardware here if any */
+          .... /* (not implemented in this document) */
+
+          /* release the irq */
+          if (chip->irq >= 0)
+                  free_irq(chip->irq, chip);
+          /* release the I/O ports & memory */
+          pci_release_regions(chip->pci);
+          /* disable the PCI entry */
+          pci_disable_device(chip->pci);
+          /* release the data */
+          kfree(chip);
+          return 0;
+  }
+
+  /* chip-specific constructor */
+  static int __devinit snd_mychip_create(struct snd_card *card,
+                                         struct pci_dev *pci,
+                                         struct mychip **rchip)
+  {
+          struct mychip *chip;
+          int err;
+          static struct snd_device_ops ops = {
+                 .dev_free = snd_mychip_dev_free,
+          };
+
+          *rchip = NULL;
+
+          /* initialize the PCI entry */
+          err = pci_enable_device(pci);
+          if (err < 0)
+                  return err;
+          /* check PCI availability (28bit DMA) */
+          if (pci_set_dma_mask(pci, DMA_28BIT_MASK) < 0 ||
+              pci_set_consistent_dma_mask(pci, DMA_28BIT_MASK) < 0) {
+                  printk(KERN_ERR "error to set 28bit mask DMA\n");
+                  pci_disable_device(pci);
+                  return -ENXIO;
+          }
+
+          chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+          if (chip == NULL) {
+                  pci_disable_device(pci);
+                  return -ENOMEM;
+          }
+
+          /* initialize the stuff */
+          chip->card = card;
+          chip->pci = pci;
+          chip->irq = -1;
+
+          /* (1) PCI resource allocation */
+          err = pci_request_regions(pci, "My Chip");
+          if (err < 0) {
+                  kfree(chip);
+                  pci_disable_device(pci);
+                  return err;
+          }
+          chip->port = pci_resource_start(pci, 0);
+          if (request_irq(pci->irq, snd_mychip_interrupt,
+                          IRQF_SHARED, "My Chip", chip)) {
+                  printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
+                  snd_mychip_free(chip);
+                  return -EBUSY;
+          }
+          chip->irq = pci->irq;
+
+          /* (2) initialization of the chip hardware */
+          .... /*   (not implemented in this document) */
+
+          err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+          if (err < 0) {
+                  snd_mychip_free(chip);
+                  return err;
+          }
+
+          snd_card_set_dev(card, &pci->dev);
+
+          *rchip = chip;
+          return 0;
+  }        
+
+  /* PCI IDs */
+  static struct pci_device_id snd_mychip_ids[] = {
+          { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
+            PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
+          ....
+          { 0, }
+  };
+  MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
+
+  /* pci_driver definition */
+  static struct pci_driver driver = {
+          .name = "My Own Chip",
+          .id_table = snd_mychip_ids,
+          .probe = snd_mychip_probe,
+          .remove = __devexit_p(snd_mychip_remove),
+  };
+
+  /* module initialization */
+  static int __init alsa_card_mychip_init(void)
+  {
+          return pci_register_driver(&driver);
+  }
+
+  /* module clean up */
+  static void __exit alsa_card_mychip_exit(void)
+  {
+          pci_unregister_driver(&driver);
+  }
+
+  module_init(alsa_card_mychip_init)
+  module_exit(alsa_card_mychip_exit)
+
+  EXPORT_NO_SYMBOLS; /* for old kernels only */
+]]>
+          </programlisting>
+        </example>
+      </para>
+    </section>
+
+    <section id="pci-resource-some-haftas">
+      <title>Some Hafta's</title>
+      <para>
+        The allocation of PCI resources is done in the
+      <function>probe()</function> function, and usually an extra
+      <function>xxx_create()</function> function is written for this
+      purpose.
+      </para>
+
+      <para>
+        In the case of PCI devices, you first have to call
+      the <function>pci_enable_device()</function> function before
+      allocating resources. Also, you need to set the proper PCI DMA
+      mask to limit the accessed I/O range. In some cases, you might
+      need to call <function>pci_set_master()</function> function,
+      too.
+      </para>
+
+      <para>
+        Suppose the 28bit mask, and the code to be added would be like:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  err = pci_enable_device(pci);
+  if (err < 0)
+          return err;
+  if (pci_set_dma_mask(pci, DMA_28BIT_MASK) < 0 ||
+      pci_set_consistent_dma_mask(pci, DMA_28BIT_MASK) < 0) {
+          printk(KERN_ERR "error to set 28bit mask DMA\n");
+          pci_disable_device(pci);
+          return -ENXIO;
+  }
+  
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+    </section>
+
+    <section id="pci-resource-resource-allocation">
+      <title>Resource Allocation</title>
+      <para>
+        The allocation of I/O ports and irqs is done via standard kernel
+      functions. Unlike ALSA ver.0.5.x., there are no helpers for
+      that. And these resources must be released in the destructor
+      function (see below). Also, on ALSA 0.9.x, you don't need to
+      allocate (pseudo-)DMA for PCI like in ALSA 0.5.x.
+      </para>
+
+      <para>
+        Now assume that the PCI device has an I/O port with 8 bytes
+        and an interrupt. Then struct <structname>mychip</structname> will have the
+        following fields:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct mychip {
+          struct snd_card *card;
+
+          unsigned long port;
+          int irq;
+  };
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        For an I/O port (and also a memory region), you need to have
+      the resource pointer for the standard resource management. For
+      an irq, you have to keep only the irq number (integer). But you
+      need to initialize this number as -1 before actual allocation,
+      since irq 0 is valid. The port address and its resource pointer
+      can be initialized as null by
+      <function>kzalloc()</function> automatically, so you
+      don't have to take care of resetting them. 
+      </para>
+
+      <para>
+        The allocation of an I/O port is done like this:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  err = pci_request_regions(pci, "My Chip");
+  if (err < 0) { 
+          kfree(chip);
+          pci_disable_device(pci);
+          return err;
+  }
+  chip->port = pci_resource_start(pci, 0);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        <!-- obsolete -->
+        It will reserve the I/O port region of 8 bytes of the given
+      PCI device. The returned value, chip-&gt;res_port, is allocated
+      via <function>kmalloc()</function> by
+      <function>request_region()</function>. The pointer must be
+      released via <function>kfree()</function>, but there is a
+      problem with this. This issue will be explained later.
+      </para>
+
+      <para>
+        The allocation of an interrupt source is done like this:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  if (request_irq(pci->irq, snd_mychip_interrupt,
+                  IRQF_SHARED, "My Chip", chip)) {
+          printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
+          snd_mychip_free(chip);
+          return -EBUSY;
+  }
+  chip->irq = pci->irq;
+]]>
+          </programlisting>
+        </informalexample>
+
+        where <function>snd_mychip_interrupt()</function> is the
+      interrupt handler defined <link
+      linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>.
+      Note that chip-&gt;irq should be defined
+      only when <function>request_irq()</function> succeeded.
+      </para>
+
+      <para>
+      On the PCI bus, interrupts can be shared. Thus,
+      <constant>IRQF_SHARED</constant> is used as the interrupt flag of
+      <function>request_irq()</function>. 
+      </para>
+
+      <para>
+        The last argument of <function>request_irq()</function> is the
+      data pointer passed to the interrupt handler. Usually, the
+      chip-specific record is used for that, but you can use what you
+      like, too. 
+      </para>
+
+      <para>
+        I won't give details about the interrupt handler at this
+        point, but at least its appearance can be explained now. The
+        interrupt handler looks usually like the following: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+  {
+          struct mychip *chip = dev_id;
+          ....
+          return IRQ_HANDLED;
+  }
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        Now let's write the corresponding destructor for the resources
+      above. The role of destructor is simple: disable the hardware
+      (if already activated) and release the resources. So far, we
+      have no hardware part, so the disabling code is not written here. 
+      </para>
+
+      <para>
+        To release the resources, the <quote>check-and-release</quote>
+        method is a safer way. For the interrupt, do like this: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  if (chip->irq >= 0)
+          free_irq(chip->irq, chip);
+]]>
+          </programlisting>
+        </informalexample>
+
+        Since the irq number can start from 0, you should initialize
+        chip-&gt;irq with a negative value (e.g. -1), so that you can
+        check the validity of the irq number as above.
+      </para>
+
+      <para>
+        When you requested I/O ports or memory regions via
+	<function>pci_request_region()</function> or
+	<function>pci_request_regions()</function> like in this example,
+	release the resource(s) using the corresponding function,
+	<function>pci_release_region()</function> or
+	<function>pci_release_regions()</function>.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  pci_release_regions(chip->pci);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+	When you requested manually via <function>request_region()</function>
+	or <function>request_mem_region</function>, you can release it via
+	<function>release_resource()</function>.  Suppose that you keep
+	the resource pointer returned from <function>request_region()</function>
+	in chip-&gt;res_port, the release procedure looks like:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  release_and_free_resource(chip->res_port);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+      Don't forget to call <function>pci_disable_device()</function>
+      before the end.
+      </para>
+
+      <para>
+        And finally, release the chip-specific record.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  kfree(chip);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+      Again, remember that you cannot
+      use the <parameter>__devexit</parameter> prefix for this destructor. 
+      </para>
+
+      <para>
+      We didn't implement the hardware disabling part in the above.
+      If you need to do this, please note that the destructor may be
+      called even before the initialization of the chip is completed.
+      It would be better to have a flag to skip hardware disabling
+      if the hardware was not initialized yet.
+      </para>
+
+      <para>
+      When the chip-data is assigned to the card using
+      <function>snd_device_new()</function> with
+      <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is 
+      called at the last.  That is, it is assured that all other
+      components like PCMs and controls have already been released.
+      You don't have to stop PCMs, etc. explicitly, but just
+      call low-level hardware stopping.
+      </para>
+
+      <para>
+        The management of a memory-mapped region is almost as same as
+        the management of an I/O port. You'll need three fields like
+        the following: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct mychip {
+          ....
+          unsigned long iobase_phys;
+          void __iomem *iobase_virt;
+  };
+]]>
+          </programlisting>
+        </informalexample>
+
+        and the allocation would be like below:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  if ((err = pci_request_regions(pci, "My Chip")) < 0) {
+          kfree(chip);
+          return err;
+  }
+  chip->iobase_phys = pci_resource_start(pci, 0);
+  chip->iobase_virt = ioremap_nocache(chip->iobase_phys,
+                                      pci_resource_len(pci, 0));
+]]>
+          </programlisting>
+        </informalexample>
+        
+        and the corresponding destructor would be:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int snd_mychip_free(struct mychip *chip)
+  {
+          ....
+          if (chip->iobase_virt)
+                  iounmap(chip->iobase_virt);
+          ....
+          pci_release_regions(chip->pci);
+          ....
+  }
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+    </section>
+
+    <section id="pci-resource-device-struct">
+      <title>Registration of Device Struct</title>
+      <para>
+	At some point, typically after calling <function>snd_device_new()</function>,
+	you need to register the struct <structname>device</structname> of the chip
+	you're handling for udev and co.  ALSA provides a macro for compatibility with
+	older kernels.  Simply call like the following:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_card_set_dev(card, &pci->dev);
+]]>
+          </programlisting>
+        </informalexample>
+	so that it stores the PCI's device pointer to the card.  This will be
+	referred by ALSA core functions later when the devices are registered.
+      </para>
+      <para>
+	In the case of non-PCI, pass the proper device struct pointer of the BUS
+	instead.  (In the case of legacy ISA without PnP, you don't have to do
+	anything.)
+      </para>
+    </section>
+
+    <section id="pci-resource-entries">
+      <title>PCI Entries</title>
+      <para>
+        So far, so good. Let's finish the missing PCI
+      stuff. At first, we need a
+      <structname>pci_device_id</structname> table for this
+      chipset. It's a table of PCI vendor/device ID number, and some
+      masks. 
+      </para>
+
+      <para>
+        For example,
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static struct pci_device_id snd_mychip_ids[] = {
+          { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
+            PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
+          ....
+          { 0, }
+  };
+  MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The first and second fields of
+      the <structname>pci_device_id</structname> structure are the vendor and
+      device IDs. If you have no reason to filter the matching
+      devices, you can leave the remaining fields as above. The last
+      field of the <structname>pci_device_id</structname> struct contains
+      private data for this entry. You can specify any value here, for
+      example, to define specific operations for supported device IDs.
+      Such an example is found in the intel8x0 driver. 
+      </para>
+
+      <para>
+        The last entry of this list is the terminator. You must
+      specify this all-zero entry. 
+      </para>
+
+      <para>
+        Then, prepare the <structname>pci_driver</structname> record:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static struct pci_driver driver = {
+          .name = "My Own Chip",
+          .id_table = snd_mychip_ids,
+          .probe = snd_mychip_probe,
+          .remove = __devexit_p(snd_mychip_remove),
+  };
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The <structfield>probe</structfield> and
+      <structfield>remove</structfield> functions have already
+      been defined in the previous sections.
+      The <structfield>remove</structfield> function should
+      be defined with the 
+      <function>__devexit_p()</function> macro, so that it's not
+      defined for built-in (and non-hot-pluggable) case. The
+      <structfield>name</structfield> 
+      field is the name string of this device. Note that you must not
+      use a slash <quote>/</quote> in this string. 
+      </para>
+
+      <para>
+        And at last, the module entries:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int __init alsa_card_mychip_init(void)
+  {
+          return pci_register_driver(&driver);
+  }
+
+  static void __exit alsa_card_mychip_exit(void)
+  {
+          pci_unregister_driver(&driver);
+  }
+
+  module_init(alsa_card_mychip_init)
+  module_exit(alsa_card_mychip_exit)
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        Note that these module entries are tagged with
+      <parameter>__init</parameter> and 
+      <parameter>__exit</parameter> prefixes, not
+      <parameter>__devinit</parameter> nor
+      <parameter>__devexit</parameter>.
+      </para>
+
+      <para>
+        Oh, one thing was forgotten. If you have no exported symbols,
+        you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels).
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  EXPORT_NO_SYMBOLS;
+]]>
+          </programlisting>
+        </informalexample>
+
+        That's all!
+      </para>
+    </section>
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- PCM Interface  -->
+<!-- ****************************************************** -->
+  <chapter id="pcm-interface">
+    <title>PCM Interface</title>
+
+    <section id="pcm-interface-general">
+      <title>General</title>
+      <para>
+        The PCM middle layer of ALSA is quite powerful and it is only
+      necessary for each driver to implement the low-level functions
+      to access its hardware.
+      </para>
+
+      <para>
+        For accessing to the PCM layer, you need to include
+      <filename>&lt;sound/pcm.h&gt;</filename> first. In addition,
+      <filename>&lt;sound/pcm_params.h&gt;</filename> might be needed
+      if you access to some functions related with hw_param. 
+      </para>
+
+      <para>
+        Each card device can have up to four pcm instances. A pcm
+      instance corresponds to a pcm device file. The limitation of
+      number of instances comes only from the available bit size of
+      the Linux's device numbers. Once when 64bit device number is
+      used, we'll have more pcm instances available. 
+      </para>
+
+      <para>
+        A pcm instance consists of pcm playback and capture streams,
+      and each pcm stream consists of one or more pcm substreams. Some
+      soundcards support multiple playback functions. For example,
+      emu10k1 has a PCM playback of 32 stereo substreams. In this case, at
+      each open, a free substream is (usually) automatically chosen
+      and opened. Meanwhile, when only one substream exists and it was
+      already opened, the successful open will either block
+      or error with <constant>EAGAIN</constant> according to the
+      file open mode. But you don't have to care about such details in your
+      driver. The PCM middle layer will take care of such work.
+      </para>
+    </section>
+
+    <section id="pcm-interface-example">
+      <title>Full Code Example</title>
+      <para>
+      The example code below does not include any hardware access
+      routines but shows only the skeleton, how to build up the PCM
+      interfaces.
+
+        <example>
+          <title>PCM Example Code</title>
+          <programlisting>
+<![CDATA[
+  #include <sound/pcm.h>
+  ....
+
+  /* hardware definition */
+  static struct snd_pcm_hardware snd_mychip_playback_hw = {
+          .info = (SNDRV_PCM_INFO_MMAP |
+                   SNDRV_PCM_INFO_INTERLEAVED |
+                   SNDRV_PCM_INFO_BLOCK_TRANSFER |
+                   SNDRV_PCM_INFO_MMAP_VALID),
+          .formats =          SNDRV_PCM_FMTBIT_S16_LE,
+          .rates =            SNDRV_PCM_RATE_8000_48000,
+          .rate_min =         8000,
+          .rate_max =         48000,
+          .channels_min =     2,
+          .channels_max =     2,
+          .buffer_bytes_max = 32768,
+          .period_bytes_min = 4096,
+          .period_bytes_max = 32768,
+          .periods_min =      1,
+          .periods_max =      1024,
+  };
+
+  /* hardware definition */
+  static struct snd_pcm_hardware snd_mychip_capture_hw = {
+          .info = (SNDRV_PCM_INFO_MMAP |
+                   SNDRV_PCM_INFO_INTERLEAVED |
+                   SNDRV_PCM_INFO_BLOCK_TRANSFER |
+                   SNDRV_PCM_INFO_MMAP_VALID),
+          .formats =          SNDRV_PCM_FMTBIT_S16_LE,
+          .rates =            SNDRV_PCM_RATE_8000_48000,
+          .rate_min =         8000,
+          .rate_max =         48000,
+          .channels_min =     2,
+          .channels_max =     2,
+          .buffer_bytes_max = 32768,
+          .period_bytes_min = 4096,
+          .period_bytes_max = 32768,
+          .periods_min =      1,
+          .periods_max =      1024,
+  };
+
+  /* open callback */
+  static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          struct snd_pcm_runtime *runtime = substream->runtime;
+
+          runtime->hw = snd_mychip_playback_hw;
+          /* more hardware-initialization will be done here */
+          ....
+          return 0;
+  }
+
+  /* close callback */
+  static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          /* the hardware-specific codes will be here */
+          ....
+          return 0;
+
+  }
+
+  /* open callback */
+  static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          struct snd_pcm_runtime *runtime = substream->runtime;
+
+          runtime->hw = snd_mychip_capture_hw;
+          /* more hardware-initialization will be done here */
+          ....
+          return 0;
+  }
+
+  /* close callback */
+  static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          /* the hardware-specific codes will be here */
+          ....
+          return 0;
+
+  }
+
+  /* hw_params callback */
+  static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
+                               struct snd_pcm_hw_params *hw_params)
+  {
+          return snd_pcm_lib_malloc_pages(substream,
+                                     params_buffer_bytes(hw_params));
+  }
+
+  /* hw_free callback */
+  static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
+  {
+          return snd_pcm_lib_free_pages(substream);
+  }
+
+  /* prepare callback */
+  static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          struct snd_pcm_runtime *runtime = substream->runtime;
+
+          /* set up the hardware with the current configuration
+           * for example...
+           */
+          mychip_set_sample_format(chip, runtime->format);
+          mychip_set_sample_rate(chip, runtime->rate);
+          mychip_set_channels(chip, runtime->channels);
+          mychip_set_dma_setup(chip, runtime->dma_addr,
+                               chip->buffer_size,
+                               chip->period_size);
+          return 0;
+  }
+
+  /* trigger callback */
+  static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
+                                    int cmd)
+  {
+          switch (cmd) {
+          case SNDRV_PCM_TRIGGER_START:
+                  /* do something to start the PCM engine */
+                  ....
+                  break;
+          case SNDRV_PCM_TRIGGER_STOP:
+                  /* do something to stop the PCM engine */
+                  ....
+                  break;
+          default:
+                  return -EINVAL;
+          }
+  }
+
+  /* pointer callback */
+  static snd_pcm_uframes_t
+  snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          unsigned int current_ptr;
+
+          /* get the current hardware pointer */
+          current_ptr = mychip_get_hw_pointer(chip);
+          return current_ptr;
+  }
+
+  /* operators */
+  static struct snd_pcm_ops snd_mychip_playback_ops = {
+          .open =        snd_mychip_playback_open,
+          .close =       snd_mychip_playback_close,
+          .ioctl =       snd_pcm_lib_ioctl,
+          .hw_params =   snd_mychip_pcm_hw_params,
+          .hw_free =     snd_mychip_pcm_hw_free,
+          .prepare =     snd_mychip_pcm_prepare,
+          .trigger =     snd_mychip_pcm_trigger,
+          .pointer =     snd_mychip_pcm_pointer,
+  };
+
+  /* operators */
+  static struct snd_pcm_ops snd_mychip_capture_ops = {
+          .open =        snd_mychip_capture_open,
+          .close =       snd_mychip_capture_close,
+          .ioctl =       snd_pcm_lib_ioctl,
+          .hw_params =   snd_mychip_pcm_hw_params,
+          .hw_free =     snd_mychip_pcm_hw_free,
+          .prepare =     snd_mychip_pcm_prepare,
+          .trigger =     snd_mychip_pcm_trigger,
+          .pointer =     snd_mychip_pcm_pointer,
+  };
+
+  /*
+   *  definitions of capture are omitted here...
+   */
+
+  /* create a pcm device */
+  static int __devinit snd_mychip_new_pcm(struct mychip *chip)
+  {
+          struct snd_pcm *pcm;
+          int err;
+
+          err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
+          if (err < 0) 
+                  return err;
+          pcm->private_data = chip;
+          strcpy(pcm->name, "My Chip");
+          chip->pcm = pcm;
+          /* set operators */
+          snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
+                          &snd_mychip_playback_ops);
+          snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
+                          &snd_mychip_capture_ops);
+          /* pre-allocation of buffers */
+          /* NOTE: this may fail */
+          snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+                                                snd_dma_pci_data(chip->pci),
+                                                64*1024, 64*1024);
+          return 0;
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+    </section>
+
+    <section id="pcm-interface-constructor">
+      <title>Constructor</title>
+      <para>
+        A pcm instance is allocated by the <function>snd_pcm_new()</function>
+      function. It would be better to create a constructor for pcm,
+      namely, 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int __devinit snd_mychip_new_pcm(struct mychip *chip)
+  {
+          struct snd_pcm *pcm;
+          int err;
+
+          err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
+          if (err < 0) 
+                  return err;
+          pcm->private_data = chip;
+          strcpy(pcm->name, "My Chip");
+          chip->pcm = pcm;
+	  ....
+          return 0;
+  }
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The <function>snd_pcm_new()</function> function takes four
+      arguments. The first argument is the card pointer to which this
+      pcm is assigned, and the second is the ID string. 
+      </para>
+
+      <para>
+        The third argument (<parameter>index</parameter>, 0 in the
+      above) is the index of this new pcm. It begins from zero. If
+      you create more than one pcm instances, specify the
+      different numbers in this argument. For example,
+      <parameter>index</parameter> = 1 for the second PCM device.  
+      </para>
+
+      <para>
+        The fourth and fifth arguments are the number of substreams
+      for playback and capture, respectively. Here 1 is used for
+      both arguments. When no playback or capture substreams are available,
+      pass 0 to the corresponding argument.
+      </para>
+
+      <para>
+        If a chip supports multiple playbacks or captures, you can
+      specify more numbers, but they must be handled properly in
+      open/close, etc. callbacks.  When you need to know which
+      substream you are referring to, then it can be obtained from
+      struct <structname>snd_pcm_substream</structname> data passed to each callback
+      as follows: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_pcm_substream *substream;
+  int index = substream->number;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        After the pcm is created, you need to set operators for each
+        pcm stream. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
+                  &snd_mychip_playback_ops);
+  snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
+                  &snd_mychip_capture_ops);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The operators are defined typically like this:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static struct snd_pcm_ops snd_mychip_playback_ops = {
+          .open =        snd_mychip_pcm_open,
+          .close =       snd_mychip_pcm_close,
+          .ioctl =       snd_pcm_lib_ioctl,
+          .hw_params =   snd_mychip_pcm_hw_params,
+          .hw_free =     snd_mychip_pcm_hw_free,
+          .prepare =     snd_mychip_pcm_prepare,
+          .trigger =     snd_mychip_pcm_trigger,
+          .pointer =     snd_mychip_pcm_pointer,
+  };
+]]>
+          </programlisting>
+        </informalexample>
+
+        All the callbacks are described in the
+        <link linkend="pcm-interface-operators"><citetitle>
+        Operators</citetitle></link> subsection.
+      </para>
+
+      <para>
+        After setting the operators, you probably will want to
+        pre-allocate the buffer. For the pre-allocation, simply call
+        the following: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+                                        snd_dma_pci_data(chip->pci),
+                                        64*1024, 64*1024);
+]]>
+          </programlisting>
+        </informalexample>
+
+        It will allocate a buffer up to 64kB as default.
+      Buffer management details will be described in the later section <link
+      linkend="buffer-and-memory"><citetitle>Buffer and Memory
+      Management</citetitle></link>. 
+      </para>
+
+      <para>
+        Additionally, you can set some extra information for this pcm
+        in pcm-&gt;info_flags.
+        The available values are defined as
+        <constant>SNDRV_PCM_INFO_XXX</constant> in
+        <filename>&lt;sound/asound.h&gt;</filename>, which is used for
+        the hardware definition (described later). When your soundchip
+        supports only half-duplex, specify like this: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+    </section>
+
+    <section id="pcm-interface-destructor">
+      <title>... And the Destructor?</title>
+      <para>
+        The destructor for a pcm instance is not always
+      necessary. Since the pcm device will be released by the middle
+      layer code automatically, you don't have to call the destructor
+      explicitly.
+      </para>
+
+      <para>
+        The destructor would be necessary if you created
+        special records internally and needed to release them. In such a
+        case, set the destructor function to
+        pcm-&gt;private_free: 
+
+        <example>
+          <title>PCM Instance with a Destructor</title>
+          <programlisting>
+<![CDATA[
+  static void mychip_pcm_free(struct snd_pcm *pcm)
+  {
+          struct mychip *chip = snd_pcm_chip(pcm);
+          /* free your own data */
+          kfree(chip->my_private_pcm_data);
+          /* do what you like else */
+          ....
+  }
+
+  static int __devinit snd_mychip_new_pcm(struct mychip *chip)
+  {
+          struct snd_pcm *pcm;
+          ....
+          /* allocate your own data */
+          chip->my_private_pcm_data = kmalloc(...);
+          /* set the destructor */
+          pcm->private_data = chip;
+          pcm->private_free = mychip_pcm_free;
+          ....
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+    </section>
+
+    <section id="pcm-interface-runtime">
+      <title>Runtime Pointer - The Chest of PCM Information</title>
+	<para>
+	  When the PCM substream is opened, a PCM runtime instance is
+	allocated and assigned to the substream. This pointer is
+	accessible via <constant>substream-&gt;runtime</constant>.
+	This runtime pointer holds most information you need
+	to control the PCM: the copy of hw_params and sw_params configurations, the buffer
+	pointers, mmap records, spinlocks, etc.
+	</para>
+
+	<para>
+	The definition of runtime instance is found in
+	<filename>&lt;sound/pcm.h&gt;</filename>.  Here are
+       the contents of this file:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+struct _snd_pcm_runtime {
+	/* -- Status -- */
+	struct snd_pcm_substream *trigger_master;
+	snd_timestamp_t trigger_tstamp;	/* trigger timestamp */
+	int overrange;
+	snd_pcm_uframes_t avail_max;
+	snd_pcm_uframes_t hw_ptr_base;	/* Position at buffer restart */
+	snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
+
+	/* -- HW params -- */
+	snd_pcm_access_t access;	/* access mode */
+	snd_pcm_format_t format;	/* SNDRV_PCM_FORMAT_* */
+	snd_pcm_subformat_t subformat;	/* subformat */
+	unsigned int rate;		/* rate in Hz */
+	unsigned int channels;		/* channels */
+	snd_pcm_uframes_t period_size;	/* period size */
+	unsigned int periods;		/* periods */
+	snd_pcm_uframes_t buffer_size;	/* buffer size */
+	unsigned int tick_time;		/* tick time */
+	snd_pcm_uframes_t min_align;	/* Min alignment for the format */
+	size_t byte_align;
+	unsigned int frame_bits;
+	unsigned int sample_bits;
+	unsigned int info;
+	unsigned int rate_num;
+	unsigned int rate_den;
+
+	/* -- SW params -- */
+	struct timespec tstamp_mode;	/* mmap timestamp is updated */
+  	unsigned int period_step;
+	unsigned int sleep_min;		/* min ticks to sleep */
+	snd_pcm_uframes_t start_threshold;
+	snd_pcm_uframes_t stop_threshold;
+	snd_pcm_uframes_t silence_threshold; /* Silence filling happens when
+						noise is nearest than this */
+	snd_pcm_uframes_t silence_size;	/* Silence filling size */
+	snd_pcm_uframes_t boundary;	/* pointers wrap point */
+
+	snd_pcm_uframes_t silenced_start;
+	snd_pcm_uframes_t silenced_size;
+
+	snd_pcm_sync_id_t sync;		/* hardware synchronization ID */
+
+	/* -- mmap -- */
+	volatile struct snd_pcm_mmap_status *status;
+	volatile struct snd_pcm_mmap_control *control;
+	atomic_t mmap_count;
+
+	/* -- locking / scheduling -- */
+	spinlock_t lock;
+	wait_queue_head_t sleep;
+	struct timer_list tick_timer;
+	struct fasync_struct *fasync;
+
+	/* -- private section -- */
+	void *private_data;
+	void (*private_free)(struct snd_pcm_runtime *runtime);
+
+	/* -- hardware description -- */
+	struct snd_pcm_hardware hw;
+	struct snd_pcm_hw_constraints hw_constraints;
+
+	/* -- interrupt callbacks -- */
+	void (*transfer_ack_begin)(struct snd_pcm_substream *substream);
+	void (*transfer_ack_end)(struct snd_pcm_substream *substream);
+
+	/* -- timer -- */
+	unsigned int timer_resolution;	/* timer resolution */
+
+	/* -- DMA -- */           
+	unsigned char *dma_area;	/* DMA area */
+	dma_addr_t dma_addr;		/* physical bus address (not accessible from main CPU) */
+	size_t dma_bytes;		/* size of DMA area */
+
+	struct snd_dma_buffer *dma_buffer_p;	/* allocated buffer */
+
+#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
+	/* -- OSS things -- */
+	struct snd_pcm_oss_runtime oss;
+#endif
+};
+]]>
+            </programlisting>
+          </informalexample>
+	</para>
+
+	<para>
+	  For the operators (callbacks) of each sound driver, most of
+	these records are supposed to be read-only.  Only the PCM
+	middle-layer changes / updates them.  The exceptions are
+	the hardware description (hw), interrupt callbacks
+	(transfer_ack_xxx), DMA buffer information, and the private
+	data.  Besides, if you use the standard buffer allocation
+	method via <function>snd_pcm_lib_malloc_pages()</function>,
+	you don't need to set the DMA buffer information by yourself.
+	</para>
+
+	<para>
+	In the sections below, important records are explained.
+	</para>
+
+	<section id="pcm-interface-runtime-hw">
+	<title>Hardware Description</title>
+	<para>
+	  The hardware descriptor (struct <structname>snd_pcm_hardware</structname>)
+	contains the definitions of the fundamental hardware
+	configuration.  Above all, you'll need to define this in
+	<link linkend="pcm-interface-operators-open-callback"><citetitle>
+	the open callback</citetitle></link>.
+	Note that the runtime instance holds the copy of the
+	descriptor, not the pointer to the existing descriptor.  That
+	is, in the open callback, you can modify the copied descriptor
+	(<constant>runtime-&gt;hw</constant>) as you need.  For example, if the maximum
+	number of channels is 1 only on some chip models, you can
+	still use the same hardware descriptor and change the
+	channels_max later:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+          struct snd_pcm_runtime *runtime = substream->runtime;
+          ...
+          runtime->hw = snd_mychip_playback_hw; /* common definition */
+          if (chip->model == VERY_OLD_ONE)
+                  runtime->hw.channels_max = 1;
+]]>
+            </programlisting>
+          </informalexample>
+	</para>
+
+	<para>
+	  Typically, you'll have a hardware descriptor as below:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static struct snd_pcm_hardware snd_mychip_playback_hw = {
+          .info = (SNDRV_PCM_INFO_MMAP |
+                   SNDRV_PCM_INFO_INTERLEAVED |
+                   SNDRV_PCM_INFO_BLOCK_TRANSFER |
+                   SNDRV_PCM_INFO_MMAP_VALID),
+          .formats =          SNDRV_PCM_FMTBIT_S16_LE,
+          .rates =            SNDRV_PCM_RATE_8000_48000,
+          .rate_min =         8000,
+          .rate_max =         48000,
+          .channels_min =     2,
+          .channels_max =     2,
+          .buffer_bytes_max = 32768,
+          .period_bytes_min = 4096,
+          .period_bytes_max = 32768,
+          .periods_min =      1,
+          .periods_max =      1024,
+  };
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+	<itemizedlist>
+	<listitem><para>
+          The <structfield>info</structfield> field contains the type and
+        capabilities of this pcm. The bit flags are defined in
+        <filename>&lt;sound/asound.h&gt;</filename> as
+        <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you
+        have to specify whether the mmap is supported and which
+        interleaved format is supported.
+        When the is supported, add the
+        <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the
+        hardware supports the interleaved or the non-interleaved
+        formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or
+        <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must
+        be set, respectively. If both are supported, you can set both,
+        too. 
+        </para>
+
+        <para>
+          In the above example, <constant>MMAP_VALID</constant> and
+        <constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap
+        mode. Usually both are set. Of course,
+        <constant>MMAP_VALID</constant> is set only if the mmap is
+        really supported. 
+        </para>
+
+        <para>
+          The other possible flags are
+        <constant>SNDRV_PCM_INFO_PAUSE</constant> and
+        <constant>SNDRV_PCM_INFO_RESUME</constant>. The
+        <constant>PAUSE</constant> bit means that the pcm supports the
+        <quote>pause</quote> operation, while the
+        <constant>RESUME</constant> bit means that the pcm supports
+        the full <quote>suspend/resume</quote> operation.
+	If the <constant>PAUSE</constant> flag is set,
+	the <structfield>trigger</structfield> callback below
+        must handle the corresponding (pause push/release) commands.
+	The suspend/resume trigger commands can be defined even without
+	the <constant>RESUME</constant> flag.  See <link
+	linkend="power-management"><citetitle>
+	Power Management</citetitle></link> section for details.
+        </para>
+
+	<para>
+	  When the PCM substreams can be synchronized (typically,
+	synchronized start/stop of a playback and a capture streams),
+	you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>,
+	too.  In this case, you'll need to check the linked-list of
+	PCM substreams in the trigger callback.  This will be
+	described in the later section.
+	</para>
+	</listitem>
+
+	<listitem>
+        <para>
+          <structfield>formats</structfield> field contains the bit-flags
+        of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>).
+        If the hardware supports more than one format, give all or'ed
+        bits.  In the example above, the signed 16bit little-endian
+        format is specified.
+        </para>
+	</listitem>
+
+	<listitem>
+        <para>
+        <structfield>rates</structfield> field contains the bit-flags of
+        supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>).
+        When the chip supports continuous rates, pass
+        <constant>CONTINUOUS</constant> bit additionally.
+        The pre-defined rate bits are provided only for typical
+	rates. If your chip supports unconventional rates, you need to add
+        the <constant>KNOT</constant> bit and set up the hardware
+        constraint manually (explained later).
+        </para>
+	</listitem>
+
+	<listitem>
+	<para>
+	<structfield>rate_min</structfield> and
+	<structfield>rate_max</structfield> define the minimum and
+	maximum sample rate.  This should correspond somehow to
+	<structfield>rates</structfield> bits.
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	<structfield>channel_min</structfield> and
+	<structfield>channel_max</structfield> 
+	define, as you might already expected, the minimum and maximum
+	number of channels.
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	<structfield>buffer_bytes_max</structfield> defines the
+	maximum buffer size in bytes.  There is no
+	<structfield>buffer_bytes_min</structfield> field, since
+	it can be calculated from the minimum period size and the
+	minimum number of periods.
+	Meanwhile, <structfield>period_bytes_min</structfield> and
+	define the minimum and maximum size of the period in bytes.
+	<structfield>periods_max</structfield> and
+	<structfield>periods_min</structfield> define the maximum and
+	minimum number of periods in the buffer.
+        </para>
+
+	<para>
+	The <quote>period</quote> is a term that corresponds to
+	a fragment in the OSS world. The period defines the size at
+	which a PCM interrupt is generated. This size strongly
+	depends on the hardware. 
+	Generally, the smaller period size will give you more
+	interrupts, that is, more controls. 
+	In the case of capture, this size defines the input latency.
+	On the other hand, the whole buffer size defines the
+	output latency for the playback direction.
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	There is also a field <structfield>fifo_size</structfield>.
+	This specifies the size of the hardware FIFO, but currently it
+	is neither used in the driver nor in the alsa-lib.  So, you
+	can ignore this field.
+	</para>
+	</listitem>
+	</itemizedlist>
+	</para>
+	</section>
+
+	<section id="pcm-interface-runtime-config">
+	<title>PCM Configurations</title>
+	<para>
+	Ok, let's go back again to the PCM runtime records.
+	The most frequently referred records in the runtime instance are
+	the PCM configurations.
+	The PCM configurations are stored in the runtime instance
+	after the application sends <type>hw_params</type> data via
+	alsa-lib.  There are many fields copied from hw_params and
+	sw_params structs.  For example,
+	<structfield>format</structfield> holds the format type
+	chosen by the application.  This field contains the enum value
+	<constant>SNDRV_PCM_FORMAT_XXX</constant>.
+	</para>
+
+	<para>
+	One thing to be noted is that the configured buffer and period
+	sizes are stored in <quote>frames</quote> in the runtime.
+        In the ALSA world, 1 frame = channels * samples-size.
+	For conversion between frames and bytes, you can use the
+	<function>frames_to_bytes()</function> and
+          <function>bytes_to_frames()</function> helper functions. 
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  period_bytes = frames_to_bytes(runtime, runtime->period_size);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+	<para>
+	Also, many software parameters (sw_params) are
+	stored in frames, too.  Please check the type of the field.
+	<type>snd_pcm_uframes_t</type> is for the frames as unsigned
+	integer while <type>snd_pcm_sframes_t</type> is for the frames
+	as signed integer.
+	</para>
+	</section>
+
+	<section id="pcm-interface-runtime-dma">
+	<title>DMA Buffer Information</title>
+	<para>
+	The DMA buffer is defined by the following four fields,
+	<structfield>dma_area</structfield>,
+	<structfield>dma_addr</structfield>,
+	<structfield>dma_bytes</structfield> and
+	<structfield>dma_private</structfield>.
+	The <structfield>dma_area</structfield> holds the buffer
+	pointer (the logical address).  You can call
+	<function>memcpy</function> from/to 
+	this pointer.  Meanwhile, <structfield>dma_addr</structfield>
+	holds the physical address of the buffer.  This field is
+	specified only when the buffer is a linear buffer.
+	<structfield>dma_bytes</structfield> holds the size of buffer
+	in bytes.  <structfield>dma_private</structfield> is used for
+	the ALSA DMA allocator.
+	</para>
+
+	<para>
+	If you use a standard ALSA function,
+	<function>snd_pcm_lib_malloc_pages()</function>, for
+	allocating the buffer, these fields are set by the ALSA middle
+	layer, and you should <emphasis>not</emphasis> change them by
+	yourself.  You can read them but not write them.
+	On the other hand, if you want to allocate the buffer by
+	yourself, you'll need to manage it in hw_params callback.
+	At least, <structfield>dma_bytes</structfield> is mandatory.
+	<structfield>dma_area</structfield> is necessary when the
+	buffer is mmapped.  If your driver doesn't support mmap, this
+	field is not necessary.  <structfield>dma_addr</structfield>
+	is also optional.  You can use
+	<structfield>dma_private</structfield> as you like, too.
+	</para>
+	</section>
+
+	<section id="pcm-interface-runtime-status">
+	<title>Running Status</title>
+	<para>
+	The running status can be referred via <constant>runtime-&gt;status</constant>.
+	This is the pointer to the struct <structname>snd_pcm_mmap_status</structname>
+	record.  For example, you can get the current DMA hardware
+	pointer via <constant>runtime-&gt;status-&gt;hw_ptr</constant>.
+	</para>
+
+	<para>
+	The DMA application pointer can be referred via
+	<constant>runtime-&gt;control</constant>, which points to the
+	struct <structname>snd_pcm_mmap_control</structname> record.
+	However, accessing directly to this value is not recommended.
+	</para>
+	</section>
+
+	<section id="pcm-interface-runtime-private">
+	<title>Private Data</title> 
+	<para>
+	You can allocate a record for the substream and store it in
+	<constant>runtime-&gt;private_data</constant>.  Usually, this
+	is done in
+	<link linkend="pcm-interface-operators-open-callback"><citetitle>
+	the open callback</citetitle></link>.
+	Don't mix this with <constant>pcm-&gt;private_data</constant>.
+	The <constant>pcm-&gt;private_data</constant> usually points to the
+	chip instance assigned statically at the creation of PCM, while the 
+	<constant>runtime-&gt;private_data</constant> points to a dynamic
+	data structure created at the PCM open callback.
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_open(struct snd_pcm_substream *substream)
+  {
+          struct my_pcm_data *data;
+          ....
+          data = kmalloc(sizeof(*data), GFP_KERNEL);
+          substream->runtime->private_data = data;
+          ....
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          The allocated object must be released in
+	<link linkend="pcm-interface-operators-open-callback"><citetitle>
+	the close callback</citetitle></link>.
+        </para>
+	</section>
+
+	<section id="pcm-interface-runtime-intr">
+	<title>Interrupt Callbacks</title>
+	<para>
+	The field <structfield>transfer_ack_begin</structfield> and
+	<structfield>transfer_ack_end</structfield> are called at
+	the beginning and at the end of
+	<function>snd_pcm_period_elapsed()</function>, respectively. 
+	</para>
+	</section>
+
+    </section>
+
+    <section id="pcm-interface-operators">
+      <title>Operators</title>
+      <para>
+        OK, now let me give details about each pcm callback
+      (<parameter>ops</parameter>). In general, every callback must
+      return 0 if successful, or a negative error number
+      such as <constant>-EINVAL</constant>. To choose an appropriate
+      error number, it is advised to check what value other parts of
+      the kernel return when the same kind of request fails.
+      </para>
+
+      <para>
+        The callback function takes at least the argument with
+        <structname>snd_pcm_substream</structname> pointer. To retrieve
+        the chip record from the given substream instance, you can use the
+        following macro. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  int xxx() {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          ....
+  }
+]]>
+          </programlisting>
+        </informalexample>
+
+	The macro reads <constant>substream-&gt;private_data</constant>,
+	which is a copy of <constant>pcm-&gt;private_data</constant>.
+	You can override the former if you need to assign different data
+	records per PCM substream.  For example, the cmi8330 driver assigns
+	different private_data for playback and capture directions,
+	because it uses two different codecs (SB- and AD-compatible) for
+	different directions.
+      </para>
+
+      <section id="pcm-interface-operators-open-callback">
+        <title>open callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_open(struct snd_pcm_substream *substream);
+]]>
+            </programlisting>
+          </informalexample>
+
+          This is called when a pcm substream is opened.
+        </para>
+
+        <para>
+          At least, here you have to initialize the runtime-&gt;hw
+          record. Typically, this is done by like this: 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_open(struct snd_pcm_substream *substream)
+  {
+          struct mychip *chip = snd_pcm_substream_chip(substream);
+          struct snd_pcm_runtime *runtime = substream->runtime;
+
+          runtime->hw = snd_mychip_playback_hw;
+          return 0;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+
+          where <parameter>snd_mychip_playback_hw</parameter> is the
+          pre-defined hardware description.
+	</para>
+
+	<para>
+	You can allocate a private data in this callback, as described
+	in <link linkend="pcm-interface-runtime-private"><citetitle>
+	Private Data</citetitle></link> section.
+	</para>
+
+	<para>
+	If the hardware configuration needs more constraints, set the
+	hardware constraints here, too.
+	See <link linkend="pcm-interface-constraints"><citetitle>
+	Constraints</citetitle></link> for more details.
+	</para>
+      </section>
+
+      <section id="pcm-interface-operators-close-callback">
+        <title>close callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_close(struct snd_pcm_substream *substream);
+]]>
+            </programlisting>
+          </informalexample>
+
+          Obviously, this is called when a pcm substream is closed.
+        </para>
+
+        <para>
+          Any private instance for a pcm substream allocated in the
+          open callback will be released here. 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_close(struct snd_pcm_substream *substream)
+  {
+          ....
+          kfree(substream->runtime->private_data);
+          ....
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-ioctl-callback">
+        <title>ioctl callback</title>
+        <para>
+          This is used for any special call to pcm ioctls. But
+        usually you can pass a generic ioctl callback, 
+        <function>snd_pcm_lib_ioctl</function>.
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-hw-params-callback">
+        <title>hw_params callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_hw_params(struct snd_pcm_substream *substream,
+                               struct snd_pcm_hw_params *hw_params);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          This is called when the hardware parameter
+        (<structfield>hw_params</structfield>) is set
+        up by the application, 
+        that is, once when the buffer size, the period size, the
+        format, etc. are defined for the pcm substream. 
+        </para>
+
+        <para>
+          Many hardware setups should be done in this callback,
+        including the allocation of buffers. 
+        </para>
+
+        <para>
+          Parameters to be initialized are retrieved by
+          <function>params_xxx()</function> macros. To allocate
+          buffer, you can call a helper function, 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params));
+]]>
+            </programlisting>
+          </informalexample>
+
+          <function>snd_pcm_lib_malloc_pages()</function> is available
+	  only when the DMA buffers have been pre-allocated.
+	  See the section <link
+	  linkend="buffer-and-memory-buffer-types"><citetitle>
+	  Buffer Types</citetitle></link> for more details.
+        </para>
+
+        <para>
+          Note that this and <structfield>prepare</structfield> callbacks
+        may be called multiple times per initialization.
+        For example, the OSS emulation may
+        call these callbacks at each change via its ioctl. 
+        </para>
+
+        <para>
+          Thus, you need to be careful not to allocate the same buffers
+        many times, which will lead to memory leaks!  Calling the
+        helper function above many times is OK. It will release the
+        previous buffer automatically when it was already allocated. 
+        </para>
+
+        <para>
+          Another note is that this callback is non-atomic
+        (schedulable). This is important, because the
+        <structfield>trigger</structfield> callback 
+        is atomic (non-schedulable). That is, mutexes or any
+        schedule-related functions are not available in
+        <structfield>trigger</structfield> callback.
+	Please see the subsection
+	<link linkend="pcm-interface-atomicity"><citetitle>
+	Atomicity</citetitle></link> for details.
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-hw-free-callback">
+        <title>hw_free callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_hw_free(struct snd_pcm_substream *substream);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          This is called to release the resources allocated via
+          <structfield>hw_params</structfield>. For example, releasing the
+          buffer via 
+          <function>snd_pcm_lib_malloc_pages()</function> is done by
+          calling the following: 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  snd_pcm_lib_free_pages(substream);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          This function is always called before the close callback is called.
+          Also, the callback may be called multiple times, too.
+          Keep track whether the resource was already released. 
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-prepare-callback">
+       <title>prepare callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_prepare(struct snd_pcm_substream *substream);
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          This callback is called when the pcm is
+        <quote>prepared</quote>. You can set the format type, sample
+        rate, etc. here. The difference from
+        <structfield>hw_params</structfield> is that the 
+        <structfield>prepare</structfield> callback will be called each
+        time 
+        <function>snd_pcm_prepare()</function> is called, i.e. when
+        recovering after underruns, etc. 
+        </para>
+
+        <para>
+	Note that this callback is now non-atomic.
+	You can use schedule-related functions safely in this callback.
+        </para>
+
+        <para>
+          In this and the following callbacks, you can refer to the
+        values via the runtime record,
+        substream-&gt;runtime.
+        For example, to get the current
+        rate, format or channels, access to
+        runtime-&gt;rate,
+        runtime-&gt;format or
+        runtime-&gt;channels, respectively. 
+        The physical address of the allocated buffer is set to
+	runtime-&gt;dma_area.  The buffer and period sizes are
+	in runtime-&gt;buffer_size and runtime-&gt;period_size,
+	respectively.
+        </para>
+
+        <para>
+          Be careful that this callback will be called many times at
+        each setup, too. 
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-trigger-callback">
+        <title>trigger callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd);
+]]>
+            </programlisting>
+          </informalexample>
+
+          This is called when the pcm is started, stopped or paused.
+        </para>
+
+        <para>
+          Which action is specified in the second argument,
+          <constant>SNDRV_PCM_TRIGGER_XXX</constant> in
+          <filename>&lt;sound/pcm.h&gt;</filename>. At least,
+          the <constant>START</constant> and <constant>STOP</constant>
+          commands must be defined in this callback. 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  switch (cmd) {
+  case SNDRV_PCM_TRIGGER_START:
+          /* do something to start the PCM engine */
+          break;
+  case SNDRV_PCM_TRIGGER_STOP:
+          /* do something to stop the PCM engine */
+          break;
+  default:
+          return -EINVAL;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+          When the pcm supports the pause operation (given in the info
+        field of the hardware table), the <constant>PAUSE_PUSE</constant>
+        and <constant>PAUSE_RELEASE</constant> commands must be
+        handled here, too. The former is the command to pause the pcm,
+        and the latter to restart the pcm again. 
+        </para>
+
+        <para>
+          When the pcm supports the suspend/resume operation,
+	regardless of full or partial suspend/resume support,
+        the <constant>SUSPEND</constant> and <constant>RESUME</constant>
+        commands must be handled, too.
+        These commands are issued when the power-management status is
+        changed.  Obviously, the <constant>SUSPEND</constant> and
+        <constant>RESUME</constant> commands
+        suspend and resume the pcm substream, and usually, they
+        are identical to the <constant>STOP</constant> and
+        <constant>START</constant> commands, respectively.
+	  See the <link linkend="power-management"><citetitle>
+	Power Management</citetitle></link> section for details.
+        </para>
+
+        <para>
+          As mentioned, this callback is atomic.  You cannot call
+	  functions which may sleep.
+	  The trigger callback should be as minimal as possible,
+	  just really triggering the DMA.  The other stuff should be
+	  initialized hw_params and prepare callbacks properly
+	  beforehand.
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-pointer-callback">
+        <title>pointer callback</title>
+        <para>
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
+]]>
+            </programlisting>
+          </informalexample>
+
+          This callback is called when the PCM middle layer inquires
+        the current hardware position on the buffer. The position must
+        be returned in frames,
+        ranging from 0 to buffer_size - 1.
+        </para>
+
+        <para>
+          This is called usually from the buffer-update routine in the
+        pcm middle layer, which is invoked when
+        <function>snd_pcm_period_elapsed()</function> is called in the
+        interrupt routine. Then the pcm middle layer updates the
+        position and calculates the available space, and wakes up the
+        sleeping poll threads, etc. 
+        </para>
+
+        <para>
+          This callback is also atomic.
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-copy-silence">
+        <title>copy and silence callbacks</title>
+        <para>
+          These callbacks are not mandatory, and can be omitted in
+        most cases. These callbacks are used when the hardware buffer
+        cannot be in the normal memory space. Some chips have their
+        own buffer on the hardware which is not mappable. In such a
+        case, you have to transfer the data manually from the memory
+        buffer to the hardware buffer. Or, if the buffer is
+        non-contiguous on both physical and virtual memory spaces,
+        these callbacks must be defined, too. 
+        </para>
+
+        <para>
+          If these two callbacks are defined, copy and set-silence
+        operations are done by them. The detailed will be described in
+        the later section <link
+        linkend="buffer-and-memory"><citetitle>Buffer and Memory
+        Management</citetitle></link>. 
+        </para>
+      </section>
+
+      <section id="pcm-interface-operators-ack">
+        <title>ack callback</title>
+        <para>
+          This callback is also not mandatory. This callback is called
+        when the appl_ptr is updated in read or write operations.
+        Some drivers like emu10k1-fx and cs46xx need to track the
+	current appl_ptr for the internal buffer, and this callback
+	is useful only for such a purpose.
+	</para>
+	<para>
+	  This callback is atomic.
+	</para>
+      </section>
+
+      <section id="pcm-interface-operators-page-callback">
+        <title>page callback</title>
+
+        <para>
+          This callback is optional too. This callback is used
+        mainly for non-contiguous buffers. The mmap calls this
+        callback to get the page address. Some examples will be
+        explained in the later section <link
+        linkend="buffer-and-memory"><citetitle>Buffer and Memory
+        Management</citetitle></link>, too. 
+        </para>
+      </section>
+    </section>
+
+    <section id="pcm-interface-interrupt-handler">
+      <title>Interrupt Handler</title>
+      <para>
+        The rest of pcm stuff is the PCM interrupt handler. The
+      role of PCM interrupt handler in the sound driver is to update
+      the buffer position and to tell the PCM middle layer when the
+      buffer position goes across the prescribed period size. To
+      inform this, call the <function>snd_pcm_period_elapsed()</function>
+      function. 
+      </para>
+
+      <para>
+        There are several types of sound chips to generate the interrupts.
+      </para>
+
+      <section id="pcm-interface-interrupt-handler-boundary">
+        <title>Interrupts at the period (fragment) boundary</title>
+        <para>
+          This is the most frequently found type:  the hardware
+        generates an interrupt at each period boundary.
+	In this case, you can call
+        <function>snd_pcm_period_elapsed()</function> at each 
+        interrupt. 
+        </para>
+
+        <para>
+          <function>snd_pcm_period_elapsed()</function> takes the
+        substream pointer as its argument. Thus, you need to keep the
+        substream pointer accessible from the chip instance. For
+        example, define substream field in the chip record to hold the
+        current running substream pointer, and set the pointer value
+        at open callback (and reset at close callback). 
+        </para>
+
+        <para>
+          If you acquire a spinlock in the interrupt handler, and the
+        lock is used in other pcm callbacks, too, then you have to
+        release the lock before calling
+        <function>snd_pcm_period_elapsed()</function>, because
+        <function>snd_pcm_period_elapsed()</function> calls other pcm
+        callbacks inside. 
+        </para>
+
+        <para>
+          Typical code would be like:
+
+          <example>
+	    <title>Interrupt Handler Case #1</title>
+            <programlisting>
+<![CDATA[
+  static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+  {
+          struct mychip *chip = dev_id;
+          spin_lock(&chip->lock);
+          ....
+          if (pcm_irq_invoked(chip)) {
+                  /* call updater, unlock before it */
+                  spin_unlock(&chip->lock);
+                  snd_pcm_period_elapsed(chip->substream);
+                  spin_lock(&chip->lock);
+                  /* acknowledge the interrupt if necessary */
+          }
+          ....
+          spin_unlock(&chip->lock);
+          return IRQ_HANDLED;
+  }
+]]>
+            </programlisting>
+          </example>
+        </para>
+      </section>
+
+      <section id="pcm-interface-interrupt-handler-timer">
+        <title>High frequency timer interrupts</title>
+        <para>
+	This happense when the hardware doesn't generate interrupts
+        at the period boundary but issues timer interrupts at a fixed
+        timer rate (e.g. es1968 or ymfpci drivers). 
+        In this case, you need to check the current hardware
+        position and accumulate the processed sample length at each
+        interrupt.  When the accumulated size exceeds the period
+        size, call 
+        <function>snd_pcm_period_elapsed()</function> and reset the
+        accumulator. 
+        </para>
+
+        <para>
+          Typical code would be like the following.
+
+          <example>
+	    <title>Interrupt Handler Case #2</title>
+            <programlisting>
+<![CDATA[
+  static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+  {
+          struct mychip *chip = dev_id;
+          spin_lock(&chip->lock);
+          ....
+          if (pcm_irq_invoked(chip)) {
+                  unsigned int last_ptr, size;
+                  /* get the current hardware pointer (in frames) */
+                  last_ptr = get_hw_ptr(chip);
+                  /* calculate the processed frames since the
+                   * last update
+                   */
+                  if (last_ptr < chip->last_ptr)
+                          size = runtime->buffer_size + last_ptr 
+                                   - chip->last_ptr; 
+                  else
+                          size = last_ptr - chip->last_ptr;
+                  /* remember the last updated point */
+                  chip->last_ptr = last_ptr;
+                  /* accumulate the size */
+                  chip->size += size;
+                  /* over the period boundary? */
+                  if (chip->size >= runtime->period_size) {
+                          /* reset the accumulator */
+                          chip->size %= runtime->period_size;
+                          /* call updater */
+                          spin_unlock(&chip->lock);
+                          snd_pcm_period_elapsed(substream);
+                          spin_lock(&chip->lock);
+                  }
+                  /* acknowledge the interrupt if necessary */
+          }
+          ....
+          spin_unlock(&chip->lock);
+          return IRQ_HANDLED;
+  }
+]]>
+            </programlisting>
+          </example>
+        </para>
+      </section>
+
+      <section id="pcm-interface-interrupt-handler-both">
+        <title>On calling <function>snd_pcm_period_elapsed()</function></title>
+        <para>
+          In both cases, even if more than one period are elapsed, you
+        don't have to call
+        <function>snd_pcm_period_elapsed()</function> many times. Call
+        only once. And the pcm layer will check the current hardware
+        pointer and update to the latest status. 
+        </para>
+      </section>
+    </section>
+
+    <section id="pcm-interface-atomicity">
+      <title>Atomicity</title>
+      <para>
+      One of the most important (and thus difficult to debug) problems
+      in kernel programming are race conditions.
+      In the Linux kernel, they are usually avoided via spin-locks, mutexes
+      or semaphores.  In general, if a race condition can happen
+      in an interrupt handler, it has to be managed atomically, and you
+      have to use a spinlock to protect the critical session. If the
+      critical section is not in interrupt handler code and
+      if taking a relatively long time to execute is acceptable, you
+      should use mutexes or semaphores instead.
+      </para>
+
+      <para>
+      As already seen, some pcm callbacks are atomic and some are
+      not.  For example, the <parameter>hw_params</parameter> callback is
+      non-atomic, while <parameter>trigger</parameter> callback is
+      atomic.  This means, the latter is called already in a spinlock
+      held by the PCM middle layer. Please take this atomicity into
+      account when you choose a locking scheme in the callbacks.
+      </para>
+
+      <para>
+      In the atomic callbacks, you cannot use functions which may call
+      <function>schedule</function> or go to
+      <function>sleep</function>.  Semaphores and mutexes can sleep,
+      and hence they cannot be used inside the atomic callbacks
+      (e.g. <parameter>trigger</parameter> callback).
+      To implement some delay in such a callback, please use
+      <function>udelay()</function> or <function>mdelay()</function>.
+      </para>
+
+      <para>
+      All three atomic callbacks (trigger, pointer, and ack) are
+      called with local interrupts disabled.
+      </para>
+
+    </section>
+    <section id="pcm-interface-constraints">
+      <title>Constraints</title>
+      <para>
+        If your chip supports unconventional sample rates, or only the
+      limited samples, you need to set a constraint for the
+      condition. 
+      </para>
+
+      <para>
+        For example, in order to restrict the sample rates in the some
+        supported values, use
+	<function>snd_pcm_hw_constraint_list()</function>.
+	You need to call this function in the open callback.
+
+        <example>
+	  <title>Example of Hardware Constraints</title>
+          <programlisting>
+<![CDATA[
+  static unsigned int rates[] =
+          {4000, 10000, 22050, 44100};
+  static struct snd_pcm_hw_constraint_list constraints_rates = {
+          .count = ARRAY_SIZE(rates),
+          .list = rates,
+          .mask = 0,
+  };
+
+  static int snd_mychip_pcm_open(struct snd_pcm_substream *substream)
+  {
+          int err;
+          ....
+          err = snd_pcm_hw_constraint_list(substream->runtime, 0,
+                                           SNDRV_PCM_HW_PARAM_RATE,
+                                           &constraints_rates);
+          if (err < 0)
+                  return err;
+          ....
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+
+      <para>
+        There are many different constraints.
+        Look at <filename>sound/pcm.h</filename> for a complete list.
+        You can even define your own constraint rules.
+        For example, let's suppose my_chip can manage a substream of 1 channel
+        if and only if the format is S16_LE, otherwise it supports any format
+        specified in the <structname>snd_pcm_hardware</structname> structure (or in any
+        other constraint_list). You can build a rule like this:
+
+        <example>
+	  <title>Example of Hardware Constraints for Channels</title>
+	  <programlisting>
+<![CDATA[
+  static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,
+                                        struct snd_pcm_hw_rule *rule)
+  {
+          struct snd_interval *c = hw_param_interval(params,
+                SNDRV_PCM_HW_PARAM_CHANNELS);
+          struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+          struct snd_mask fmt;
+
+          snd_mask_any(&fmt);    /* Init the struct */
+          if (c->min < 2) {
+                  fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
+                  return snd_mask_refine(f, &fmt);
+          }
+          return 0;
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+ 
+      <para>
+        Then you need to call this function to add your rule:
+
+       <informalexample>
+	 <programlisting>
+<![CDATA[
+  snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+                      hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+                      -1);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The rule function is called when an application sets the number of
+        channels. But an application can set the format before the number of
+        channels. Thus you also need to define the inverse rule:
+
+       <example>
+	 <title>Example of Hardware Constraints for Channels</title>
+	 <programlisting>
+<![CDATA[
+  static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,
+                                        struct snd_pcm_hw_rule *rule)
+  {
+          struct snd_interval *c = hw_param_interval(params,
+                        SNDRV_PCM_HW_PARAM_CHANNELS);
+          struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+          struct snd_interval ch;
+
+          snd_interval_any(&ch);
+          if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
+                  ch.min = ch.max = 1;
+                  ch.integer = 1;
+                  return snd_interval_refine(c, &ch);
+          }
+          return 0;
+  }
+]]>
+          </programlisting>
+        </example>
+      </para>
+
+      <para>
+      ...and in the open callback:
+       <informalexample>
+	 <programlisting>
+<![CDATA[
+  snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+                      hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+                      -1);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        I won't give more details here, rather I
+        would like to say, <quote>Luke, use the source.</quote>
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Control Interface  -->
+<!-- ****************************************************** -->
+  <chapter id="control-interface">
+    <title>Control Interface</title>
+
+    <section id="control-interface-general">
+      <title>General</title>
+      <para>
+        The control interface is used widely for many switches,
+      sliders, etc. which are accessed from user-space. Its most
+      important use is the mixer interface. In other words, since ALSA
+      0.9.x, all the mixer stuff is implemented on the control kernel API.
+      </para>
+
+      <para>
+        ALSA has a well-defined AC97 control module. If your chip
+      supports only the AC97 and nothing else, you can skip this
+      section. 
+      </para>
+
+      <para>
+        The control API is defined in
+      <filename>&lt;sound/control.h&gt;</filename>.
+      Include this file if you want to add your own controls.
+      </para>
+    </section>
+
+    <section id="control-interface-definition">
+      <title>Definition of Controls</title>
+      <para>
+        To create a new control, you need to define the
+	following three
+      callbacks: <structfield>info</structfield>,
+      <structfield>get</structfield> and
+      <structfield>put</structfield>. Then, define a
+      struct <structname>snd_kcontrol_new</structname> record, such as: 
+
+        <example>
+	  <title>Definition of a Control</title>
+          <programlisting>
+<![CDATA[
+  static struct snd_kcontrol_new my_control __devinitdata = {
+          .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+          .name = "PCM Playback Switch",
+          .index = 0,
+          .access = SNDRV_CTL_ELEM_ACCESS_READWRITE,
+          .private_value = 0xffff,
+          .info = my_control_info,
+          .get = my_control_get,
+          .put = my_control_put
+  };
+]]>
+          </programlisting>
+        </example>
+      </para>
+
+      <para>
+        Most likely the control is created via
+      <function>snd_ctl_new1()</function>, and in such a case, you can
+      add the <parameter>__devinitdata</parameter> prefix to the
+      definition as above. 
+      </para>
+
+      <para>
+        The <structfield>iface</structfield> field specifies the control
+      type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which
+      is usually <constant>MIXER</constant>.
+      Use <constant>CARD</constant> for global controls that are not
+      logically part of the mixer.
+      If the control is closely associated with some specific device on
+      the sound card, use <constant>HWDEP</constant>,
+      <constant>PCM</constant>, <constant>RAWMIDI</constant>,
+      <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and
+      specify the device number with the
+      <structfield>device</structfield> and
+      <structfield>subdevice</structfield> fields.
+      </para>
+
+      <para>
+        The <structfield>name</structfield> is the name identifier
+      string. Since ALSA 0.9.x, the control name is very important,
+      because its role is classified from its name. There are
+      pre-defined standard control names. The details are described in
+      the <link linkend="control-interface-control-names"><citetitle>
+      Control Names</citetitle></link> subsection.
+      </para>
+
+      <para>
+        The <structfield>index</structfield> field holds the index number
+      of this control. If there are several different controls with
+      the same name, they can be distinguished by the index
+      number. This is the case when 
+      several codecs exist on the card. If the index is zero, you can
+      omit the definition above. 
+      </para>
+
+      <para>
+        The <structfield>access</structfield> field contains the access
+      type of this control. Give the combination of bit masks,
+      <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there.
+      The details will be explained in
+      the <link linkend="control-interface-access-flags"><citetitle>
+      Access Flags</citetitle></link> subsection.
+      </para>
+
+      <para>
+        The <structfield>private_value</structfield> field contains
+      an arbitrary long integer value for this record. When using
+      the generic <structfield>info</structfield>,
+      <structfield>get</structfield> and
+      <structfield>put</structfield> callbacks, you can pass a value 
+      through this field. If several small numbers are necessary, you can
+      combine them in bitwise. Or, it's possible to give a pointer
+      (casted to unsigned long) of some record to this field, too. 
+      </para>
+
+      <para>
+      The <structfield>tlv</structfield> field can be used to provide
+      metadata about the control; see the
+      <link linkend="control-interface-tlv">
+      <citetitle>Metadata</citetitle></link> subsection.
+      </para>
+
+      <para>
+        The other three are
+	<link linkend="control-interface-callbacks"><citetitle>
+	callback functions</citetitle></link>.
+      </para>
+    </section>
+
+    <section id="control-interface-control-names">
+      <title>Control Names</title>
+      <para>
+        There are some standards to define the control names. A
+      control is usually defined from the three parts as
+      <quote>SOURCE DIRECTION FUNCTION</quote>. 
+      </para>
+
+      <para>
+        The first, <constant>SOURCE</constant>, specifies the source
+      of the control, and is a string such as <quote>Master</quote>,
+      <quote>PCM</quote>, <quote>CD</quote> and
+      <quote>Line</quote>. There are many pre-defined sources. 
+      </para>
+
+      <para>
+        The second, <constant>DIRECTION</constant>, is one of the
+      following strings according to the direction of the control:
+      <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass
+      Playback</quote> and <quote>Bypass Capture</quote>. Or, it can
+      be omitted, meaning both playback and capture directions. 
+      </para>
+
+      <para>
+        The third, <constant>FUNCTION</constant>, is one of the
+      following strings according to the function of the control:
+      <quote>Switch</quote>, <quote>Volume</quote> and
+      <quote>Route</quote>. 
+      </para>
+
+      <para>
+        The example of control names are, thus, <quote>Master Capture
+      Switch</quote> or <quote>PCM Playback Volume</quote>. 
+      </para>
+
+      <para>
+        There are some exceptions:
+      </para>
+
+      <section id="control-interface-control-names-global">
+        <title>Global capture and playback</title>
+        <para>
+          <quote>Capture Source</quote>, <quote>Capture Switch</quote>
+        and <quote>Capture Volume</quote> are used for the global
+        capture (input) source, switch and volume. Similarly,
+        <quote>Playback Switch</quote> and <quote>Playback
+        Volume</quote> are used for the global output gain switch and
+        volume. 
+        </para>
+      </section>
+
+      <section id="control-interface-control-names-tone">
+        <title>Tone-controls</title>
+        <para>
+          tone-control switch and volumes are specified like
+        <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control -
+        Switch</quote>, <quote>Tone Control - Bass</quote>,
+        <quote>Tone Control - Center</quote>.  
+        </para>
+      </section>
+
+      <section id="control-interface-control-names-3d">
+        <title>3D controls</title>
+        <para>
+          3D-control switches and volumes are specified like <quote>3D
+        Control - XXX</quote>, e.g. <quote>3D Control -
+        Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D
+        Control - Space</quote>. 
+        </para>
+      </section>
+
+      <section id="control-interface-control-names-mic">
+        <title>Mic boost</title>
+        <para>
+          Mic-boost switch is set as <quote>Mic Boost</quote> or
+        <quote>Mic Boost (6dB)</quote>. 
+        </para>
+
+        <para>
+          More precise information can be found in
+        <filename>Documentation/sound/alsa/ControlNames.txt</filename>.
+        </para>
+      </section>
+    </section>
+
+    <section id="control-interface-access-flags">
+      <title>Access Flags</title>
+
+      <para>
+      The access flag is the bitmask which specifies the access type
+      of the given control.  The default access type is
+      <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>, 
+      which means both read and write are allowed to this control.
+      When the access flag is omitted (i.e. = 0), it is
+      considered as <constant>READWRITE</constant> access as default. 
+      </para>
+
+      <para>
+      When the control is read-only, pass
+      <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead.
+      In this case, you don't have to define
+      the <structfield>put</structfield> callback.
+      Similarly, when the control is write-only (although it's a rare
+      case), you can use the <constant>WRITE</constant> flag instead, and
+      you don't need the <structfield>get</structfield> callback.
+      </para>
+
+      <para>
+      If the control value changes frequently (e.g. the VU meter),
+      <constant>VOLATILE</constant> flag should be given.  This means
+      that the control may be changed without
+      <link linkend="control-interface-change-notification"><citetitle>
+      notification</citetitle></link>. Applications should poll such
+      a control constantly.
+      </para>
+
+      <para>
+      When the control is inactive, set
+      the <constant>INACTIVE</constant> flag, too.
+      There are <constant>LOCK</constant> and
+      <constant>OWNER</constant> flags to change the write
+      permissions.
+      </para>
+
+    </section>
+
+    <section id="control-interface-callbacks">
+      <title>Callbacks</title>
+
+      <section id="control-interface-callbacks-info">
+        <title>info callback</title>
+        <para>
+          The <structfield>info</structfield> callback is used to get
+        detailed information on this control. This must store the
+        values of the given struct <structname>snd_ctl_elem_info</structname>
+        object. For example, for a boolean control with a single
+        element: 
+
+          <example>
+	    <title>Example of info callback</title>
+            <programlisting>
+<![CDATA[
+  static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol,
+                          struct snd_ctl_elem_info *uinfo)
+  {
+          uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
+          uinfo->count = 1;
+          uinfo->value.integer.min = 0;
+          uinfo->value.integer.max = 1;
+          return 0;
+  }
+]]>
+            </programlisting>
+          </example>
+        </para>
+
+        <para>
+          The <structfield>type</structfield> field specifies the type
+        of the control. There are <constant>BOOLEAN</constant>,
+        <constant>INTEGER</constant>, <constant>ENUMERATED</constant>,
+        <constant>BYTES</constant>, <constant>IEC958</constant> and
+        <constant>INTEGER64</constant>. The
+        <structfield>count</structfield> field specifies the 
+        number of elements in this control. For example, a stereo
+        volume would have count = 2. The
+        <structfield>value</structfield> field is a union, and 
+        the values stored are depending on the type. The boolean and
+        integer types are identical. 
+        </para>
+
+        <para>
+          The enumerated type is a bit different from others.  You'll
+          need to set the string for the currently given item index. 
+
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
+                          struct snd_ctl_elem_info *uinfo)
+  {
+          static char *texts[4] = {
+                  "First", "Second", "Third", "Fourth"
+          };
+          uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
+          uinfo->count = 1;
+          uinfo->value.enumerated.items = 4;
+          if (uinfo->value.enumerated.item > 3)
+                  uinfo->value.enumerated.item = 3;
+          strcpy(uinfo->value.enumerated.name,
+                 texts[uinfo->value.enumerated.item]);
+          return 0;
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+	  Some common info callbacks are available for your convenience:
+	<function>snd_ctl_boolean_mono_info()</function> and
+	<function>snd_ctl_boolean_stereo_info()</function>.
+	Obviously, the former is an info callback for a mono channel
+	boolean item, just like <function>snd_myctl_mono_info</function>
+	above, and the latter is for a stereo channel boolean item.
+	</para>
+
+      </section>
+
+      <section id="control-interface-callbacks-get">
+        <title>get callback</title>
+
+        <para>
+          This callback is used to read the current value of the
+        control and to return to user-space. 
+        </para>
+
+        <para>
+          For example,
+
+          <example>
+	    <title>Example of get callback</title>
+            <programlisting>
+<![CDATA[
+  static int snd_myctl_get(struct snd_kcontrol *kcontrol,
+                           struct snd_ctl_elem_value *ucontrol)
+  {
+          struct mychip *chip = snd_kcontrol_chip(kcontrol);
+          ucontrol->value.integer.value[0] = get_some_value(chip);
+          return 0;
+  }
+]]>
+            </programlisting>
+          </example>
+        </para>
+
+        <para>
+	The <structfield>value</structfield> field depends on 
+        the type of control as well as on the info callback.  For example,
+	the sb driver uses this field to store the register offset,
+        the bit-shift and the bit-mask.  The
+        <structfield>private_value</structfield> field is set as follows:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  .private_value = reg | (shift << 16) | (mask << 24)
+]]>
+            </programlisting>
+          </informalexample>
+	and is retrieved in callbacks like
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol,
+                                    struct snd_ctl_elem_value *ucontrol)
+  {
+          int reg = kcontrol->private_value & 0xff;
+          int shift = (kcontrol->private_value >> 16) & 0xff;
+          int mask = (kcontrol->private_value >> 24) & 0xff;
+          ....
+  }
+]]>
+            </programlisting>
+          </informalexample>
+	</para>
+
+	<para>
+	In the <structfield>get</structfield> callback,
+	you have to fill all the elements if the
+        control has more than one elements,
+        i.e. <structfield>count</structfield> &gt; 1.
+	In the example above, we filled only one element
+        (<structfield>value.integer.value[0]</structfield>) since it's
+        assumed as <structfield>count</structfield> = 1.
+        </para>
+      </section>
+
+      <section id="control-interface-callbacks-put">
+        <title>put callback</title>
+
+        <para>
+          This callback is used to write a value from user-space.
+        </para>
+
+        <para>
+          For example,
+
+          <example>
+	    <title>Example of put callback</title>
+            <programlisting>
+<![CDATA[
+  static int snd_myctl_put(struct snd_kcontrol *kcontrol,
+                           struct snd_ctl_elem_value *ucontrol)
+  {
+          struct mychip *chip = snd_kcontrol_chip(kcontrol);
+          int changed = 0;
+          if (chip->current_value !=
+               ucontrol->value.integer.value[0]) {
+                  change_current_value(chip,
+                              ucontrol->value.integer.value[0]);
+                  changed = 1;
+          }
+          return changed;
+  }
+]]>
+            </programlisting>
+          </example>
+
+          As seen above, you have to return 1 if the value is
+        changed. If the value is not changed, return 0 instead. 
+	If any fatal error happens, return a negative error code as
+        usual.
+        </para>
+
+        <para>
+	As in the <structfield>get</structfield> callback,
+	when the control has more than one elements,
+	all elements must be evaluated in this callback, too.
+        </para>
+      </section>
+
+      <section id="control-interface-callbacks-all">
+        <title>Callbacks are not atomic</title>
+        <para>
+          All these three callbacks are basically not atomic.
+        </para>
+      </section>
+    </section>
+
+    <section id="control-interface-constructor">
+      <title>Constructor</title>
+      <para>
+        When everything is ready, finally we can create a new
+      control. To create a control, there are two functions to be
+      called, <function>snd_ctl_new1()</function> and
+      <function>snd_ctl_add()</function>. 
+      </para>
+
+      <para>
+        In the simplest way, you can do like this:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
+  if (err < 0)
+          return err;
+]]>
+          </programlisting>
+        </informalexample>
+
+        where <parameter>my_control</parameter> is the
+      struct <structname>snd_kcontrol_new</structname> object defined above, and chip
+      is the object pointer to be passed to
+      kcontrol-&gt;private_data 
+      which can be referred to in callbacks. 
+      </para>
+
+      <para>
+        <function>snd_ctl_new1()</function> allocates a new
+      <structname>snd_kcontrol</structname> instance (that's why the definition
+      of <parameter>my_control</parameter> can be with
+      the <parameter>__devinitdata</parameter> 
+      prefix), and <function>snd_ctl_add</function> assigns the given
+      control component to the card. 
+      </para>
+    </section>
+
+    <section id="control-interface-change-notification">
+      <title>Change Notification</title>
+      <para>
+        If you need to change and update a control in the interrupt
+      routine, you can call <function>snd_ctl_notify()</function>. For
+      example, 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer);
+]]>
+          </programlisting>
+        </informalexample>
+
+        This function takes the card pointer, the event-mask, and the
+      control id pointer for the notification. The event-mask
+      specifies the types of notification, for example, in the above
+      example, the change of control values is notified.
+      The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname>
+      to be notified.
+      You can find some examples in <filename>es1938.c</filename> or
+      <filename>es1968.c</filename> for hardware volume interrupts. 
+      </para>
+    </section>
+
+    <section id="control-interface-tlv">
+      <title>Metadata</title>
+      <para>
+      To provide information about the dB values of a mixer control, use
+      on of the <constant>DECLARE_TLV_xxx</constant> macros from
+      <filename>&lt;sound/tlv.h&gt;</filename> to define a variable
+      containing this information, set the<structfield>tlv.p
+      </structfield> field to point to this variable, and include the
+      <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
+      <structfield>access</structfield> field; like this:
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
+
+  static struct snd_kcontrol_new my_control __devinitdata = {
+          ...
+          .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+                    SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+          ...
+          .tlv.p = db_scale_my_control,
+  };
+]]>
+        </programlisting>
+      </informalexample>
+      </para>
+
+      <para>
+      The <function>DECLARE_TLV_DB_SCALE</function> macro defines
+      information about a mixer control where each step in the control's
+      value changes the dB value by a constant dB amount.
+      The first parameter is the name of the variable to be defined.
+      The second parameter is the minimum value, in units of 0.01 dB.
+      The third parameter is the step size, in units of 0.01 dB.
+      Set the fourth parameter to 1 if the minimum value actually mutes
+      the control.
+      </para>
+
+      <para>
+      The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
+      information about a mixer control where the control's value affects
+      the output linearly.
+      The first parameter is the name of the variable to be defined.
+      The second parameter is the minimum value, in units of 0.01 dB.
+      The third parameter is the maximum value, in units of 0.01 dB.
+      If the minimum value mutes the control, set the second parameter to
+      <constant>TLV_DB_GAIN_MUTE</constant>.
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- API for AC97 Codec  -->
+<!-- ****************************************************** -->
+  <chapter id="api-ac97">
+    <title>API for AC97 Codec</title>
+
+    <section>
+      <title>General</title>
+      <para>
+        The ALSA AC97 codec layer is a well-defined one, and you don't
+      have to write much code to control it. Only low-level control
+      routines are necessary. The AC97 codec API is defined in
+      <filename>&lt;sound/ac97_codec.h&gt;</filename>. 
+      </para>
+    </section>
+
+    <section id="api-ac97-example">
+      <title>Full Code Example</title>
+      <para>
+          <example>
+	    <title>Example of AC97 Interface</title>
+            <programlisting>
+<![CDATA[
+  struct mychip {
+          ....
+          struct snd_ac97 *ac97;
+          ....
+  };
+
+  static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
+                                             unsigned short reg)
+  {
+          struct mychip *chip = ac97->private_data;
+          ....
+          /* read a register value here from the codec */
+          return the_register_value;
+  }
+
+  static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
+                                   unsigned short reg, unsigned short val)
+  {
+          struct mychip *chip = ac97->private_data;
+          ....
+          /* write the given register value to the codec */
+  }
+
+  static int snd_mychip_ac97(struct mychip *chip)
+  {
+          struct snd_ac97_bus *bus;
+          struct snd_ac97_template ac97;
+          int err;
+          static struct snd_ac97_bus_ops ops = {
+                  .write = snd_mychip_ac97_write,
+                  .read = snd_mychip_ac97_read,
+          };
+
+          err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
+          if (err < 0)
+                  return err;
+          memset(&ac97, 0, sizeof(ac97));
+          ac97.private_data = chip;
+          return snd_ac97_mixer(bus, &ac97, &chip->ac97);
+  }
+
+]]>
+          </programlisting>
+        </example>
+      </para>
+    </section>
+
+    <section id="api-ac97-constructor">
+      <title>Constructor</title>
+      <para>
+        To create an ac97 instance, first call <function>snd_ac97_bus</function>
+      with an <type>ac97_bus_ops_t</type> record with callback functions.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_ac97_bus *bus;
+  static struct snd_ac97_bus_ops ops = {
+        .write = snd_mychip_ac97_write,
+        .read = snd_mychip_ac97_read,
+  };
+
+  snd_ac97_bus(card, 0, &ops, NULL, &pbus);
+]]>
+          </programlisting>
+        </informalexample>
+
+      The bus record is shared among all belonging ac97 instances.
+      </para>
+
+      <para>
+      And then call <function>snd_ac97_mixer()</function> with an
+      struct <structname>snd_ac97_template</structname>
+      record together with the bus pointer created above.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_ac97_template ac97;
+  int err;
+
+  memset(&ac97, 0, sizeof(ac97));
+  ac97.private_data = chip;
+  snd_ac97_mixer(bus, &ac97, &chip->ac97);
+]]>
+          </programlisting>
+        </informalexample>
+
+        where chip-&gt;ac97 is a pointer to a newly created
+        <type>ac97_t</type> instance.
+        In this case, the chip pointer is set as the private data, so that
+        the read/write callback functions can refer to this chip instance.
+        This instance is not necessarily stored in the chip
+	record.  If you need to change the register values from the
+        driver, or need the suspend/resume of ac97 codecs, keep this
+        pointer to pass to the corresponding functions.
+      </para>
+    </section>
+
+    <section id="api-ac97-callbacks">
+      <title>Callbacks</title>
+      <para>
+        The standard callbacks are <structfield>read</structfield> and
+      <structfield>write</structfield>. Obviously they 
+      correspond to the functions for read and write accesses to the
+      hardware low-level codes. 
+      </para>
+
+      <para>
+        The <structfield>read</structfield> callback returns the
+        register value specified in the argument. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
+                                             unsigned short reg)
+  {
+          struct mychip *chip = ac97->private_data;
+          ....
+          return the_register_value;
+  }
+]]>
+          </programlisting>
+        </informalexample>
+
+        Here, the chip can be cast from ac97-&gt;private_data.
+      </para>
+
+      <para>
+        Meanwhile, the <structfield>write</structfield> callback is
+        used to set the register value. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
+                       unsigned short reg, unsigned short val)
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+      These callbacks are non-atomic like the control API callbacks.
+      </para>
+
+      <para>
+        There are also other callbacks:
+      <structfield>reset</structfield>,
+      <structfield>wait</structfield> and
+      <structfield>init</structfield>. 
+      </para>
+
+      <para>
+        The <structfield>reset</structfield> callback is used to reset
+      the codec. If the chip requires a special kind of reset, you can
+      define this callback. 
+      </para>
+
+      <para>
+        The <structfield>wait</structfield> callback is used to
+      add some waiting time in the standard initialization of the codec. If the
+      chip requires the extra waiting time, define this callback. 
+      </para>
+
+      <para>
+        The <structfield>init</structfield> callback is used for
+      additional initialization of the codec.
+      </para>
+    </section>
+
+    <section id="api-ac97-updating-registers">
+      <title>Updating Registers in The Driver</title>
+      <para>
+        If you need to access to the codec from the driver, you can
+      call the following functions:
+      <function>snd_ac97_write()</function>,
+      <function>snd_ac97_read()</function>,
+      <function>snd_ac97_update()</function> and
+      <function>snd_ac97_update_bits()</function>. 
+      </para>
+
+      <para>
+        Both <function>snd_ac97_write()</function> and
+        <function>snd_ac97_update()</function> functions are used to
+        set a value to the given register
+        (<constant>AC97_XXX</constant>). The difference between them is
+        that <function>snd_ac97_update()</function> doesn't write a
+        value if the given value has been already set, while
+        <function>snd_ac97_write()</function> always rewrites the
+        value. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_ac97_write(ac97, AC97_MASTER, 0x8080);
+  snd_ac97_update(ac97, AC97_MASTER, 0x8080);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        <function>snd_ac97_read()</function> is used to read the value
+        of the given register. For example, 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  value = snd_ac97_read(ac97, AC97_MASTER);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        <function>snd_ac97_update_bits()</function> is used to update
+        some bits in the given register.  
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_ac97_update_bits(ac97, reg, mask, value);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        Also, there is a function to change the sample rate (of a
+        given register such as
+        <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or
+        DRA is supported by the codec:
+        <function>snd_ac97_set_rate()</function>. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The following registers are available to set the rate:
+      <constant>AC97_PCM_MIC_ADC_RATE</constant>,
+      <constant>AC97_PCM_FRONT_DAC_RATE</constant>,
+      <constant>AC97_PCM_LR_ADC_RATE</constant>,
+      <constant>AC97_SPDIF</constant>. When
+      <constant>AC97_SPDIF</constant> is specified, the register is
+      not really changed but the corresponding IEC958 status bits will
+      be updated. 
+      </para>
+    </section>
+
+    <section id="api-ac97-clock-adjustment">
+      <title>Clock Adjustment</title>
+      <para>
+        In some chips, the clock of the codec isn't 48000 but using a
+      PCI clock (to save a quartz!). In this case, change the field
+      bus-&gt;clock to the corresponding
+      value. For example, intel8x0 
+      and es1968 drivers have their own function to read from the clock.
+      </para>
+    </section>
+
+    <section id="api-ac97-proc-files">
+      <title>Proc Files</title>
+      <para>
+        The ALSA AC97 interface will create a proc file such as
+      <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and
+      <filename>ac97#0-0+regs</filename>. You can refer to these files to
+      see the current status and registers of the codec. 
+      </para>
+    </section>
+
+    <section id="api-ac97-multiple-codecs">
+      <title>Multiple Codecs</title>
+      <para>
+        When there are several codecs on the same card, you need to
+      call <function>snd_ac97_mixer()</function> multiple times with
+      ac97.num=1 or greater. The <structfield>num</structfield> field
+      specifies the codec number. 
+      </para>
+
+      <para>
+        If you set up multiple codecs, you either need to write
+      different callbacks for each codec or check
+      ac97-&gt;num in the callback routines. 
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- MIDI (MPU401-UART) Interface  -->
+<!-- ****************************************************** -->
+  <chapter id="midi-interface">
+    <title>MIDI (MPU401-UART) Interface</title>
+
+    <section id="midi-interface-general">
+      <title>General</title>
+      <para>
+        Many soundcards have built-in MIDI (MPU401-UART)
+      interfaces. When the soundcard supports the standard MPU401-UART
+      interface, most likely you can use the ALSA MPU401-UART API. The
+      MPU401-UART API is defined in
+      <filename>&lt;sound/mpu401.h&gt;</filename>. 
+      </para>
+
+      <para>
+        Some soundchips have a similar but slightly different
+      implementation of mpu401 stuff. For example, emu10k1 has its own
+      mpu401 routines. 
+      </para>
+    </section>
+
+    <section id="midi-interface-constructor">
+      <title>Constructor</title>
+      <para>
+        To create a rawmidi object, call
+      <function>snd_mpu401_uart_new()</function>. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_rawmidi *rmidi;
+  snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
+                      irq, irq_flags, &rmidi);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The first argument is the card pointer, and the second is the
+      index of this component. You can create up to 8 rawmidi
+      devices. 
+      </para>
+
+      <para>
+        The third argument is the type of the hardware,
+      <constant>MPU401_HW_XXX</constant>. If it's not a special one,
+      you can use <constant>MPU401_HW_MPU401</constant>. 
+      </para>
+
+      <para>
+        The 4th argument is the I/O port address. Many
+      backward-compatible MPU401 have an I/O port such as 0x330. Or, it
+      might be a part of its own PCI I/O region. It depends on the
+      chip design. 
+      </para>
+
+      <para>
+	The 5th argument is a bitflag for additional information.
+        When the I/O port address above is part of the PCI I/O
+      region, the MPU401 I/O port might have been already allocated
+      (reserved) by the driver itself. In such a case, pass a bit flag
+      <constant>MPU401_INFO_INTEGRATED</constant>,
+      and the mpu401-uart layer will allocate the I/O ports by itself. 
+      </para>
+
+	<para>
+	When the controller supports only the input or output MIDI stream,
+	pass the <constant>MPU401_INFO_INPUT</constant> or
+	<constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively.
+	Then the rawmidi instance is created as a single stream.
+	</para>
+
+	<para>
+	<constant>MPU401_INFO_MMIO</constant> bitflag is used to change
+	the access method to MMIO (via readb and writeb) instead of
+	iob and outb. In this case, you have to pass the iomapped address
+	to <function>snd_mpu401_uart_new()</function>.
+	</para>
+
+	<para>
+	When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output
+	stream isn't checked in the default interrupt handler.  The driver
+	needs to call <function>snd_mpu401_uart_interrupt_tx()</function>
+	by itself to start processing the output stream in the irq handler.
+	</para>
+
+      <para>
+        Usually, the port address corresponds to the command port and
+        port + 1 corresponds to the data port. If not, you may change
+        the <structfield>cport</structfield> field of
+        struct <structname>snd_mpu401</structname> manually 
+        afterward. However, <structname>snd_mpu401</structname> pointer is not
+        returned explicitly by
+        <function>snd_mpu401_uart_new()</function>. You need to cast
+        rmidi-&gt;private_data to
+        <structname>snd_mpu401</structname> explicitly, 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_mpu401 *mpu;
+  mpu = rmidi->private_data;
+]]>
+          </programlisting>
+        </informalexample>
+
+        and reset the cport as you like:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  mpu->cport = my_own_control_port;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The 6th argument specifies the irq number for UART. If the irq
+      is already allocated, pass 0 to the 7th argument
+      (<parameter>irq_flags</parameter>). Otherwise, pass the flags
+      for irq allocation 
+      (<constant>SA_XXX</constant> bits) to it, and the irq will be
+      reserved by the mpu401-uart layer. If the card doesn't generate
+      UART interrupts, pass -1 as the irq number. Then a timer
+      interrupt will be invoked for polling. 
+      </para>
+    </section>
+
+    <section id="midi-interface-interrupt-handler">
+      <title>Interrupt Handler</title>
+      <para>
+        When the interrupt is allocated in
+      <function>snd_mpu401_uart_new()</function>, the private
+      interrupt handler is used, hence you don't have anything else to do
+      than creating the mpu401 stuff. Otherwise, you have to call
+      <function>snd_mpu401_uart_interrupt()</function> explicitly when
+      a UART interrupt is invoked and checked in your own interrupt
+      handler.  
+      </para>
+
+      <para>
+        In this case, you need to pass the private_data of the
+        returned rawmidi object from
+        <function>snd_mpu401_uart_new()</function> as the second
+        argument of <function>snd_mpu401_uart_interrupt()</function>. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- RawMIDI Interface  -->
+<!-- ****************************************************** -->
+  <chapter id="rawmidi-interface">
+    <title>RawMIDI Interface</title>
+
+    <section id="rawmidi-interface-overview">
+      <title>Overview</title>
+
+      <para>
+      The raw MIDI interface is used for hardware MIDI ports that can
+      be accessed as a byte stream.  It is not used for synthesizer
+      chips that do not directly understand MIDI.
+      </para>
+
+      <para>
+      ALSA handles file and buffer management.  All you have to do is
+      to write some code to move data between the buffer and the
+      hardware.
+      </para>
+
+      <para>
+      The rawmidi API is defined in
+      <filename>&lt;sound/rawmidi.h&gt;</filename>.
+      </para>
+    </section>
+
+    <section id="rawmidi-interface-constructor">
+      <title>Constructor</title>
+
+      <para>
+      To create a rawmidi device, call the
+      <function>snd_rawmidi_new</function> function:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_rawmidi *rmidi;
+  err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
+  if (err < 0)
+          return err;
+  rmidi->private_data = chip;
+  strcpy(rmidi->name, "My MIDI");
+  rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
+                      SNDRV_RAWMIDI_INFO_INPUT |
+                      SNDRV_RAWMIDI_INFO_DUPLEX;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+      The first argument is the card pointer, the second argument is
+      the ID string.
+      </para>
+
+      <para>
+      The third argument is the index of this component.  You can
+      create up to 8 rawmidi devices.
+      </para>
+
+      <para>
+      The fourth and fifth arguments are the number of output and
+      input substreams, respectively, of this device (a substream is
+      the equivalent of a MIDI port).
+      </para>
+
+      <para>
+      Set the <structfield>info_flags</structfield> field to specify
+      the capabilities of the device.
+      Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is
+      at least one output port,
+      <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at
+      least one input port,
+      and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device
+      can handle output and input at the same time.
+      </para>
+
+      <para>
+      After the rawmidi device is created, you need to set the
+      operators (callbacks) for each substream.  There are helper
+      functions to set the operators for all the substreams of a device:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
+  snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+      The operators are usually defined like this:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static struct snd_rawmidi_ops snd_mymidi_output_ops = {
+          .open =    snd_mymidi_output_open,
+          .close =   snd_mymidi_output_close,
+          .trigger = snd_mymidi_output_trigger,
+  };
+]]>
+          </programlisting>
+        </informalexample>
+      These callbacks are explained in the <link
+      linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link>
+      section.
+      </para>
+
+      <para>
+      If there are more than one substream, you should give a
+      unique name to each of them:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_rawmidi_substream *substream;
+  list_for_each_entry(substream,
+                      &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
+                      list {
+          sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
+  }
+  /* same for SNDRV_RAWMIDI_STREAM_INPUT */
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+    </section>
+
+    <section id="rawmidi-interface-callbacks">
+      <title>Callbacks</title>
+
+      <para>
+      In all the callbacks, the private data that you've set for the
+      rawmidi device can be accessed as
+      substream-&gt;rmidi-&gt;private_data.
+      <!-- <code> isn't available before DocBook 4.3 -->
+      </para>
+
+      <para>
+      If there is more than one port, your callbacks can determine the
+      port index from the struct snd_rawmidi_substream data passed to each
+      callback:
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_rawmidi_substream *substream;
+  int index = substream->number;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <section id="rawmidi-interface-op-open">
+      <title><function>open</function> callback</title>
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int snd_xxx_open(struct snd_rawmidi_substream *substream);
+]]>
+          </programlisting>
+        </informalexample>
+
+        <para>
+        This is called when a substream is opened.
+        You can initialize the hardware here, but you shouldn't
+        start transmitting/receiving data yet.
+        </para>
+      </section>
+
+      <section id="rawmidi-interface-op-close">
+      <title><function>close</function> callback</title>
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int snd_xxx_close(struct snd_rawmidi_substream *substream);
+]]>
+          </programlisting>
+        </informalexample>
+
+        <para>
+        Guess what.
+        </para>
+
+        <para>
+        The <function>open</function> and <function>close</function>
+        callbacks of a rawmidi device are serialized with a mutex,
+        and can sleep.
+        </para>
+      </section>
+
+      <section id="rawmidi-interface-op-trigger-out">
+      <title><function>trigger</function> callback for output
+      substreams</title>
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
+]]>
+          </programlisting>
+        </informalexample>
+
+        <para>
+        This is called with a nonzero <parameter>up</parameter>
+        parameter when there is some data in the substream buffer that
+        must be transmitted.
+        </para>
+
+        <para>
+        To read data from the buffer, call
+        <function>snd_rawmidi_transmit_peek</function>.  It will
+        return the number of bytes that have been read; this will be
+        less than the number of bytes requested when there are no more
+        data in the buffer.
+        After the data have been transmitted successfully, call
+        <function>snd_rawmidi_transmit_ack</function> to remove the
+        data from the substream buffer:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  unsigned char data;
+  while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
+          if (snd_mychip_try_to_transmit(data))
+                  snd_rawmidi_transmit_ack(substream, 1);
+          else
+                  break; /* hardware FIFO full */
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+        If you know beforehand that the hardware will accept data, you
+        can use the <function>snd_rawmidi_transmit</function> function
+        which reads some data and removes them from the buffer at once:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  while (snd_mychip_transmit_possible()) {
+          unsigned char data;
+          if (snd_rawmidi_transmit(substream, &data, 1) != 1)
+                  break; /* no more data */
+          snd_mychip_transmit(data);
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+
+        <para>
+        If you know beforehand how many bytes you can accept, you can
+        use a buffer size greater than one with the
+        <function>snd_rawmidi_transmit*</function> functions.
+        </para>
+
+        <para>
+        The <function>trigger</function> callback must not sleep.  If
+        the hardware FIFO is full before the substream buffer has been
+        emptied, you have to continue transmitting data later, either
+        in an interrupt handler, or with a timer if the hardware
+        doesn't have a MIDI transmit interrupt.
+        </para>
+
+        <para>
+        The <function>trigger</function> callback is called with a
+        zero <parameter>up</parameter> parameter when the transmission
+        of data should be aborted.
+        </para>
+      </section>
+
+      <section id="rawmidi-interface-op-trigger-in">
+      <title><function>trigger</function> callback for input
+      substreams</title>
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
+]]>
+          </programlisting>
+        </informalexample>
+
+        <para>
+        This is called with a nonzero <parameter>up</parameter>
+        parameter to enable receiving data, or with a zero
+        <parameter>up</parameter> parameter do disable receiving data.
+        </para>
+
+        <para>
+        The <function>trigger</function> callback must not sleep; the
+        actual reading of data from the device is usually done in an
+        interrupt handler.
+        </para>
+
+        <para>
+        When data reception is enabled, your interrupt handler should
+        call <function>snd_rawmidi_receive</function> for all received
+        data:
+          <informalexample>
+            <programlisting>
+<![CDATA[
+  void snd_mychip_midi_interrupt(...)
+  {
+          while (mychip_midi_available()) {
+                  unsigned char data;
+                  data = mychip_midi_read();
+                  snd_rawmidi_receive(substream, &data, 1);
+          }
+  }
+]]>
+            </programlisting>
+          </informalexample>
+        </para>
+      </section>
+
+      <section id="rawmidi-interface-op-drain">
+      <title><function>drain</function> callback</title>
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
+]]>
+          </programlisting>
+        </informalexample>
+
+        <para>
+        This is only used with output substreams.  This function should wait
+        until all data read from the substream buffer have been transmitted.
+        This ensures that the device can be closed and the driver unloaded
+        without losing data.
+        </para>
+
+        <para>
+        This callback is optional. If you do not set
+        <structfield>drain</structfield> in the struct snd_rawmidi_ops
+        structure, ALSA will simply wait for 50&nbsp;milliseconds
+        instead.
+        </para>
+      </section>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Miscellaneous Devices  -->
+<!-- ****************************************************** -->
+  <chapter id="misc-devices">
+    <title>Miscellaneous Devices</title>
+
+    <section id="misc-devices-opl3">
+      <title>FM OPL3</title>
+      <para>
+        The FM OPL3 is still used in many chips (mainly for backward
+      compatibility). ALSA has a nice OPL3 FM control layer, too. The
+      OPL3 API is defined in
+      <filename>&lt;sound/opl3.h&gt;</filename>. 
+      </para>
+
+      <para>
+        FM registers can be directly accessed through the direct-FM API,
+      defined in <filename>&lt;sound/asound_fm.h&gt;</filename>. In
+      ALSA native mode, FM registers are accessed through
+      the Hardware-Dependant Device direct-FM extension API, whereas in
+      OSS compatible mode, FM registers can be accessed with the OSS
+      direct-FM compatible API in <filename>/dev/dmfmX</filename> device. 
+      </para>
+
+      <para>
+        To create the OPL3 component, you have two functions to
+        call. The first one is a constructor for the <type>opl3_t</type>
+        instance. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_opl3 *opl3;
+  snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX,
+                  integrated, &opl3);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The first argument is the card pointer, the second one is the
+      left port address, and the third is the right port address. In
+      most cases, the right port is placed at the left port + 2. 
+      </para>
+
+      <para>
+        The fourth argument is the hardware type.
+      </para>
+
+      <para>
+        When the left and right ports have been already allocated by
+      the card driver, pass non-zero to the fifth argument
+      (<parameter>integrated</parameter>). Otherwise, the opl3 module will
+      allocate the specified ports by itself. 
+      </para>
+
+      <para>
+        When the accessing the hardware requires special method
+        instead of the standard I/O access, you can create opl3 instance
+        separately with <function>snd_opl3_new()</function>.
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_opl3 *opl3;
+  snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+	Then set <structfield>command</structfield>,
+	<structfield>private_data</structfield> and
+	<structfield>private_free</structfield> for the private
+	access function, the private data and the destructor.
+	The l_port and r_port are not necessarily set.  Only the
+	command must be set properly.  You can retrieve the data
+	from the opl3-&gt;private_data field.
+      </para>
+
+      <para>
+	After creating the opl3 instance via <function>snd_opl3_new()</function>,
+	call <function>snd_opl3_init()</function> to initialize the chip to the
+	proper state. Note that <function>snd_opl3_create()</function> always
+	calls it internally.
+      </para>
+
+      <para>
+        If the opl3 instance is created successfully, then create a
+        hwdep device for this opl3. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_hwdep *opl3hwdep;
+  snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The first argument is the <type>opl3_t</type> instance you
+      created, and the second is the index number, usually 0. 
+      </para>
+
+      <para>
+        The third argument is the index-offset for the sequencer
+      client assigned to the OPL3 port. When there is an MPU401-UART,
+      give 1 for here (UART always takes 0). 
+      </para>
+    </section>
+
+    <section id="misc-devices-hardware-dependent">
+      <title>Hardware-Dependent Devices</title>
+      <para>
+        Some chips need user-space access for special
+      controls or for loading the micro code. In such a case, you can
+      create a hwdep (hardware-dependent) device. The hwdep API is
+      defined in <filename>&lt;sound/hwdep.h&gt;</filename>. You can
+      find examples in opl3 driver or
+      <filename>isa/sb/sb16_csp.c</filename>. 
+      </para>
+
+      <para>
+        The creation of the <type>hwdep</type> instance is done via
+        <function>snd_hwdep_new()</function>. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_hwdep *hw;
+  snd_hwdep_new(card, "My HWDEP", 0, &hw);
+]]>
+          </programlisting>
+        </informalexample>
+
+        where the third argument is the index number.
+      </para>
+
+      <para>
+        You can then pass any pointer value to the
+        <parameter>private_data</parameter>.
+        If you assign a private data, you should define the
+        destructor, too. The destructor function is set in
+        the <structfield>private_free</structfield> field.  
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
+  hw->private_data = p;
+  hw->private_free = mydata_free;
+]]>
+          </programlisting>
+        </informalexample>
+
+        and the implementation of the destructor would be:
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static void mydata_free(struct snd_hwdep *hw)
+  {
+          struct mydata *p = hw->private_data;
+          kfree(p);
+  }
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The arbitrary file operations can be defined for this
+        instance. The file operators are defined in
+        the <parameter>ops</parameter> table. For example, assume that
+        this chip needs an ioctl. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  hw->ops.open = mydata_open;
+  hw->ops.ioctl = mydata_ioctl;
+  hw->ops.release = mydata_release;
+]]>
+          </programlisting>
+        </informalexample>
+
+        And implement the callback functions as you like.
+      </para>
+    </section>
+
+    <section id="misc-devices-IEC958">
+      <title>IEC958 (S/PDIF)</title>
+      <para>
+        Usually the controls for IEC958 devices are implemented via
+      the control interface. There is a macro to compose a name string for
+      IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function>
+      defined in <filename>&lt;include/asound.h&gt;</filename>.  
+      </para>
+
+      <para>
+        There are some standard controls for IEC958 status bits. These
+      controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>,
+      and the size of element is fixed as 4 bytes array
+      (value.iec958.status[x]). For the <structfield>info</structfield>
+      callback, you don't specify 
+      the value field for this type (the count field must be set,
+      though). 
+      </para>
+
+      <para>
+        <quote>IEC958 Playback Con Mask</quote> is used to return the
+      bit-mask for the IEC958 status bits of consumer mode. Similarly,
+      <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for
+      professional mode. They are read-only controls, and are defined
+      as MIXER controls (iface =
+      <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>).  
+      </para>
+
+      <para>
+        Meanwhile, <quote>IEC958 Playback Default</quote> control is
+      defined for getting and setting the current default IEC958
+      bits. Note that this one is usually defined as a PCM control
+      (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>),
+      although in some places it's defined as a MIXER control. 
+      </para>
+
+      <para>
+        In addition, you can define the control switches to
+      enable/disable or to set the raw bit mode. The implementation
+      will depend on the chip, but the control should be named as
+      <quote>IEC958 xxx</quote>, preferably using
+      the <function>SNDRV_CTL_NAME_IEC958()</function> macro. 
+      </para>
+
+      <para>
+        You can find several cases, for example,
+      <filename>pci/emu10k1</filename>,
+      <filename>pci/ice1712</filename>, or
+      <filename>pci/cmipci.c</filename>.  
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Buffer and Memory Management  -->
+<!-- ****************************************************** -->
+  <chapter id="buffer-and-memory">
+    <title>Buffer and Memory Management</title>
+
+    <section id="buffer-and-memory-buffer-types">
+      <title>Buffer Types</title>
+      <para>
+        ALSA provides several different buffer allocation functions
+      depending on the bus and the architecture. All these have a
+      consistent API. The allocation of physically-contiguous pages is
+      done via 
+      <function>snd_malloc_xxx_pages()</function> function, where xxx
+      is the bus type. 
+      </para>
+
+      <para>
+        The allocation of pages with fallback is
+      <function>snd_malloc_xxx_pages_fallback()</function>. This
+      function tries to allocate the specified pages but if the pages
+      are not available, it tries to reduce the page sizes until
+      enough space is found.
+      </para>
+
+      <para>
+      The release the pages, call
+      <function>snd_free_xxx_pages()</function> function. 
+      </para>
+
+      <para>
+      Usually, ALSA drivers try to allocate and reserve
+       a large contiguous physical space
+       at the time the module is loaded for the later use.
+       This is called <quote>pre-allocation</quote>.
+       As already written, you can call the following function at 
+       pcm instance construction time (in the case of PCI bus). 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+                                        snd_dma_pci_data(pci), size, max);
+]]>
+          </programlisting>
+        </informalexample>
+
+        where <parameter>size</parameter> is the byte size to be
+      pre-allocated and the <parameter>max</parameter> is the maximum
+      size to be changed via the <filename>prealloc</filename> proc file.
+      The allocator will try to get an area as large as possible
+      within the given size. 
+      </para>
+
+      <para>
+      The second argument (type) and the third argument (device pointer)
+      are dependent on the bus.
+      In the case of the ISA bus, pass <function>snd_dma_isa_data()</function>
+      as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type.
+      For the continuous buffer unrelated to the bus can be pre-allocated
+      with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the
+      <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer,
+      where <constant>GFP_KERNEL</constant> is the kernel allocation flag to
+      use.
+      For the PCI scatter-gather buffers, use
+      <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with
+      <function>snd_dma_pci_data(pci)</function>
+      (see the 
+          <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers
+          </citetitle></link> section).
+      </para>
+
+      <para>
+        Once the buffer is pre-allocated, you can use the
+        allocator in the <structfield>hw_params</structfield> callback: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_pcm_lib_malloc_pages(substream, size);
+]]>
+          </programlisting>
+        </informalexample>
+
+        Note that you have to pre-allocate to use this function.
+      </para>
+    </section>
+
+    <section id="buffer-and-memory-external-hardware">
+      <title>External Hardware Buffers</title>
+      <para>
+        Some chips have their own hardware buffers and the DMA
+      transfer from the host memory is not available. In such a case,
+      you need to either 1) copy/set the audio data directly to the
+      external hardware buffer, or 2) make an intermediate buffer and
+      copy/set the data from it to the external hardware buffer in
+      interrupts (or in tasklets, preferably).
+      </para>
+
+      <para>
+        The first case works fine if the external hardware buffer is large
+      enough.  This method doesn't need any extra buffers and thus is
+      more effective. You need to define the
+      <structfield>copy</structfield> and
+      <structfield>silence</structfield> callbacks for 
+      the data transfer. However, there is a drawback: it cannot
+      be mmapped. The examples are GUS's GF1 PCM or emu8000's
+      wavetable PCM. 
+      </para>
+
+      <para>
+        The second case allows for mmap on the buffer, although you have
+      to handle an interrupt or a tasklet to transfer the data
+      from the intermediate buffer to the hardware buffer. You can find an
+      example in the vxpocket driver. 
+      </para>
+
+      <para>
+        Another case is when the chip uses a PCI memory-map
+      region for the buffer instead of the host memory. In this case,
+      mmap is available only on certain architectures like the Intel one.
+      In non-mmap mode, the data cannot be transferred as in the normal
+      way. Thus you need to define the <structfield>copy</structfield> and
+      <structfield>silence</structfield> callbacks as well, 
+      as in the cases above. The examples are found in
+      <filename>rme32.c</filename> and <filename>rme96.c</filename>. 
+      </para>
+
+      <para>
+        The implementation of the <structfield>copy</structfield> and
+        <structfield>silence</structfield> callbacks depends upon 
+        whether the hardware supports interleaved or non-interleaved
+        samples. The <structfield>copy</structfield> callback is
+        defined like below, a bit 
+        differently depending whether the direction is playback or
+        capture: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int playback_copy(struct snd_pcm_substream *substream, int channel,
+               snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count);
+  static int capture_copy(struct snd_pcm_substream *substream, int channel,
+               snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        In the case of interleaved samples, the second argument
+      (<parameter>channel</parameter>) is not used. The third argument
+      (<parameter>pos</parameter>) points the 
+      current position offset in frames. 
+      </para>
+
+      <para>
+        The meaning of the fourth argument is different between
+      playback and capture. For playback, it holds the source data
+      pointer, and for capture, it's the destination data pointer. 
+      </para>
+
+      <para>
+        The last argument is the number of frames to be copied.
+      </para>
+
+      <para>
+        What you have to do in this callback is again different
+        between playback and capture directions. In the
+        playback case, you copy the given amount of data
+        (<parameter>count</parameter>) at the specified pointer
+        (<parameter>src</parameter>) to the specified offset
+        (<parameter>pos</parameter>) on the hardware buffer. When
+        coded like memcpy-like way, the copy would be like: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src,
+            frames_to_bytes(runtime, count));
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        For the capture direction, you copy the given amount of
+        data (<parameter>count</parameter>) at the specified offset
+        (<parameter>pos</parameter>) on the hardware buffer to the
+        specified pointer (<parameter>dst</parameter>). 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos),
+            frames_to_bytes(runtime, count));
+]]>
+          </programlisting>
+        </informalexample>
+
+        Note that both the position and the amount of data are given
+      in frames. 
+      </para>
+
+      <para>
+        In the case of non-interleaved samples, the implementation
+      will be a bit more complicated. 
+      </para>
+
+      <para>
+        You need to check the channel argument, and if it's -1, copy
+      the whole channels. Otherwise, you have to copy only the
+      specified channel. Please check
+      <filename>isa/gus/gus_pcm.c</filename> as an example. 
+      </para>
+
+      <para>
+        The <structfield>silence</structfield> callback is also
+        implemented in a similar way. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  static int silence(struct snd_pcm_substream *substream, int channel,
+                     snd_pcm_uframes_t pos, snd_pcm_uframes_t count);
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        The meanings of arguments are the same as in the
+      <structfield>copy</structfield> 
+      callback, although there is no <parameter>src/dst</parameter>
+      argument. In the case of interleaved samples, the channel
+      argument has no meaning, as well as on
+      <structfield>copy</structfield> callback.  
+      </para>
+
+      <para>
+        The role of <structfield>silence</structfield> callback is to
+        set the given amount 
+        (<parameter>count</parameter>) of silence data at the
+        specified offset (<parameter>pos</parameter>) on the hardware
+        buffer. Suppose that the data format is signed (that is, the
+        silent-data is 0), and the implementation using a memset-like
+        function would be like: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0,
+            frames_to_bytes(runtime, count));
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        In the case of non-interleaved samples, again, the
+      implementation becomes a bit more complicated. See, for example,
+      <filename>isa/gus/gus_pcm.c</filename>. 
+      </para>
+    </section>
+
+    <section id="buffer-and-memory-non-contiguous">
+      <title>Non-Contiguous Buffers</title>
+      <para>
+        If your hardware supports the page table as in emu10k1 or the
+      buffer descriptors as in via82xx, you can use the scatter-gather
+      (SG) DMA. ALSA provides an interface for handling SG-buffers.
+      The API is provided in <filename>&lt;sound/pcm.h&gt;</filename>. 
+      </para>
+
+      <para>
+        For creating the SG-buffer handler, call
+        <function>snd_pcm_lib_preallocate_pages()</function> or
+        <function>snd_pcm_lib_preallocate_pages_for_all()</function>
+        with <constant>SNDRV_DMA_TYPE_DEV_SG</constant>
+	in the PCM constructor like other PCI pre-allocator.
+        You need to pass <function>snd_dma_pci_data(pci)</function>,
+        where pci is the struct <structname>pci_dev</structname> pointer
+        of the chip as well.
+        The <type>struct snd_sg_buf</type> instance is created as
+        substream-&gt;dma_private. You can cast
+        the pointer like: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        Then call <function>snd_pcm_lib_malloc_pages()</function>
+      in the <structfield>hw_params</structfield> callback
+      as well as in the case of normal PCI buffer.
+      The SG-buffer handler will allocate the non-contiguous kernel
+      pages of the given size and map them onto the virtually contiguous
+      memory.  The virtual pointer is addressed in runtime-&gt;dma_area.
+      The physical address (runtime-&gt;dma_addr) is set to zero,
+      because the buffer is physically non-contigous.
+      The physical address table is set up in sgbuf-&gt;table.
+      You can get the physical address at a certain offset via
+      <function>snd_pcm_sgbuf_get_addr()</function>. 
+      </para>
+
+      <para>
+        When a SG-handler is used, you need to set
+      <function>snd_pcm_sgbuf_ops_page</function> as
+      the <structfield>page</structfield> callback.
+      (See <link linkend="pcm-interface-operators-page-callback">
+      <citetitle>page callback section</citetitle></link>.)
+      </para>
+
+      <para>
+        To release the data, call
+      <function>snd_pcm_lib_free_pages()</function> in the
+      <structfield>hw_free</structfield> callback as usual.
+      </para>
+    </section>
+
+    <section id="buffer-and-memory-vmalloced">
+      <title>Vmalloc'ed Buffers</title>
+      <para>
+        It's possible to use a buffer allocated via
+      <function>vmalloc</function>, for example, for an intermediate
+      buffer. Since the allocated pages are not contiguous, you need
+      to set the <structfield>page</structfield> callback to obtain
+      the physical address at every offset. 
+      </para>
+
+      <para>
+        The implementation of <structfield>page</structfield> callback
+        would be like this: 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  #include <linux/vmalloc.h>
+
+  /* get the physical page pointer on the given offset */
+  static struct page *mychip_page(struct snd_pcm_substream *substream,
+                                  unsigned long offset)
+  {
+          void *pageptr = substream->runtime->dma_area + offset;
+          return vmalloc_to_page(pageptr);
+  }
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Proc Interface  -->
+<!-- ****************************************************** -->
+  <chapter id="proc-interface">
+    <title>Proc Interface</title>
+    <para>
+      ALSA provides an easy interface for procfs. The proc files are
+      very useful for debugging. I recommend you set up proc files if
+      you write a driver and want to get a running status or register
+      dumps. The API is found in
+      <filename>&lt;sound/info.h&gt;</filename>. 
+    </para>
+
+    <para>
+      To create a proc file, call
+      <function>snd_card_proc_new()</function>. 
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  struct snd_info_entry *entry;
+  int err = snd_card_proc_new(card, "my-file", &entry);
+]]>
+        </programlisting>
+      </informalexample>
+
+      where the second argument specifies the name of the proc file to be
+    created. The above example will create a file
+    <filename>my-file</filename> under the card directory,
+    e.g. <filename>/proc/asound/card0/my-file</filename>. 
+    </para>
+
+    <para>
+    Like other components, the proc entry created via
+    <function>snd_card_proc_new()</function> will be registered and
+    released automatically in the card registration and release
+    functions.
+    </para>
+
+    <para>
+      When the creation is successful, the function stores a new
+    instance in the pointer given in the third argument.
+    It is initialized as a text proc file for read only.  To use
+    this proc file as a read-only text file as it is, set the read
+    callback with a private data via 
+     <function>snd_info_set_text_ops()</function>.
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  snd_info_set_text_ops(entry, chip, my_proc_read);
+]]>
+        </programlisting>
+      </informalexample>
+    
+    where the second argument (<parameter>chip</parameter>) is the
+    private data to be used in the callbacks. The third parameter
+    specifies the read buffer size and the fourth
+    (<parameter>my_proc_read</parameter>) is the callback function, which
+    is defined like
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static void my_proc_read(struct snd_info_entry *entry,
+                           struct snd_info_buffer *buffer);
+]]>
+        </programlisting>
+      </informalexample>
+    
+    </para>
+
+    <para>
+    In the read callback, use <function>snd_iprintf()</function> for
+    output strings, which works just like normal
+    <function>printf()</function>.  For example,
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static void my_proc_read(struct snd_info_entry *entry,
+                           struct snd_info_buffer *buffer)
+  {
+          struct my_chip *chip = entry->private_data;
+
+          snd_iprintf(buffer, "This is my chip!\n");
+          snd_iprintf(buffer, "Port = %ld\n", chip->port);
+  }
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+    The file permissions can be changed afterwards.  As default, it's
+    set as read only for all users.  If you want to add write
+    permission for the user (root as default), do as follows:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+ entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
+]]>
+        </programlisting>
+      </informalexample>
+
+    and set the write buffer size and the callback
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  entry->c.text.write = my_proc_write;
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+      For the write callback, you can use
+    <function>snd_info_get_line()</function> to get a text line, and
+    <function>snd_info_get_str()</function> to retrieve a string from
+    the line. Some examples are found in
+    <filename>core/oss/mixer_oss.c</filename>, core/oss/and
+    <filename>pcm_oss.c</filename>. 
+    </para>
+
+    <para>
+      For a raw-data proc-file, set the attributes as follows:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static struct snd_info_entry_ops my_file_io_ops = {
+          .read = my_file_io_read,
+  };
+
+  entry->content = SNDRV_INFO_CONTENT_DATA;
+  entry->private_data = chip;
+  entry->c.ops = &my_file_io_ops;
+  entry->size = 4096;
+  entry->mode = S_IFREG | S_IRUGO;
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+      The callback is much more complicated than the text-file
+      version. You need to use a low-level I/O functions such as
+      <function>copy_from/to_user()</function> to transfer the
+      data.
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static long my_file_io_read(struct snd_info_entry *entry,
+                              void *file_private_data,
+                              struct file *file,
+                              char *buf,
+                              unsigned long count,
+                              unsigned long pos)
+  {
+          long size = count;
+          if (pos + size > local_max_size)
+                  size = local_max_size - pos;
+          if (copy_to_user(buf, local_data + pos, size))
+                  return -EFAULT;
+          return size;
+  }
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Power Management  -->
+<!-- ****************************************************** -->
+  <chapter id="power-management">
+    <title>Power Management</title>
+    <para>
+      If the chip is supposed to work with suspend/resume
+      functions, you need to add power-management code to the
+      driver. The additional code for power-management should be
+      <function>ifdef</function>'ed with
+      <constant>CONFIG_PM</constant>. 
+    </para>
+
+	<para>
+	If the driver <emphasis>fully</emphasis> supports suspend/resume
+	that is, the device can be
+	properly resumed to its state when suspend was called,
+	you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag
+	in the pcm info field.  Usually, this is possible when the
+	registers of the chip can be safely saved and restored to
+	RAM. If this is set, the trigger callback is called with
+	<constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume
+	callback completes. 
+	</para>
+
+	<para>
+	Even if the driver doesn't support PM fully but 
+	partial suspend/resume is still possible, it's still worthy to
+	implement suspend/resume callbacks. In such a case, applications
+	would reset the status by calling
+	<function>snd_pcm_prepare()</function> and restart the stream
+	appropriately.  Hence, you can define suspend/resume callbacks
+	below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant>
+	info flag to the PCM.
+	</para>
+	
+	<para>
+	Note that the trigger with SUSPEND can always be called when
+	<function>snd_pcm_suspend_all</function> is called,
+	regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag.
+	The <constant>RESUME</constant> flag affects only the behavior
+	of <function>snd_pcm_resume()</function>.
+	(Thus, in theory,
+	<constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed
+	to be handled in the trigger callback when no
+	<constant>SNDRV_PCM_INFO_RESUME</constant> flag is set.  But,
+	it's better to keep it for compatibility reasons.)
+	</para>
+    <para>
+      In the earlier version of ALSA drivers, a common
+      power-management layer was provided, but it has been removed.
+      The driver needs to define the suspend/resume hooks according to
+      the bus the device is connected to.  In the case of PCI drivers, the
+      callbacks look like below:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  #ifdef CONFIG_PM
+  static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
+  {
+          .... /* do things for suspend */
+          return 0;
+  }
+  static int snd_my_resume(struct pci_dev *pci)
+  {
+          .... /* do things for suspend */
+          return 0;
+  }
+  #endif
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+      The scheme of the real suspend job is as follows.
+
+      <orderedlist>
+        <listitem><para>Retrieve the card and the chip data.</para></listitem>
+        <listitem><para>Call <function>snd_power_change_state()</function> with
+	  <constant>SNDRV_CTL_POWER_D3hot</constant> to change the
+	  power status.</para></listitem>
+        <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem>
+	<listitem><para>If AC97 codecs are used, call
+	<function>snd_ac97_suspend()</function> for each codec.</para></listitem>
+        <listitem><para>Save the register values if necessary.</para></listitem>
+        <listitem><para>Stop the hardware if necessary.</para></listitem>
+        <listitem><para>Disable the PCI device by calling
+	  <function>pci_disable_device()</function>.  Then, call
+          <function>pci_save_state()</function> at last.</para></listitem>
+      </orderedlist>
+    </para>
+
+    <para>
+      A typical code would be like:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static int mychip_suspend(struct pci_dev *pci, pm_message_t state)
+  {
+          /* (1) */
+          struct snd_card *card = pci_get_drvdata(pci);
+          struct mychip *chip = card->private_data;
+          /* (2) */
+          snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
+          /* (3) */
+          snd_pcm_suspend_all(chip->pcm);
+          /* (4) */
+          snd_ac97_suspend(chip->ac97);
+          /* (5) */
+          snd_mychip_save_registers(chip);
+          /* (6) */
+          snd_mychip_stop_hardware(chip);
+          /* (7) */
+          pci_disable_device(pci);
+          pci_save_state(pci);
+          return 0;
+  }
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+    The scheme of the real resume job is as follows.
+
+    <orderedlist>
+    <listitem><para>Retrieve the card and the chip data.</para></listitem>
+    <listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>.
+    	Then enable the pci device again by calling <function>pci_enable_device()</function>.
+	Call <function>pci_set_master()</function> if necessary, too.</para></listitem>
+    <listitem><para>Re-initialize the chip.</para></listitem>
+    <listitem><para>Restore the saved registers if necessary.</para></listitem>
+    <listitem><para>Resume the mixer, e.g. calling
+    <function>snd_ac97_resume()</function>.</para></listitem>
+    <listitem><para>Restart the hardware (if any).</para></listitem>
+    <listitem><para>Call <function>snd_power_change_state()</function> with
+	<constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem>
+    </orderedlist>
+    </para>
+
+    <para>
+    A typical code would be like:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static int mychip_resume(struct pci_dev *pci)
+  {
+          /* (1) */
+          struct snd_card *card = pci_get_drvdata(pci);
+          struct mychip *chip = card->private_data;
+          /* (2) */
+          pci_restore_state(pci);
+          pci_enable_device(pci);
+          pci_set_master(pci);
+          /* (3) */
+          snd_mychip_reinit_chip(chip);
+          /* (4) */
+          snd_mychip_restore_registers(chip);
+          /* (5) */
+          snd_ac97_resume(chip->ac97);
+          /* (6) */
+          snd_mychip_restart_chip(chip);
+          /* (7) */
+          snd_power_change_state(card, SNDRV_CTL_POWER_D0);
+          return 0;
+  }
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+	As shown in the above, it's better to save registers after
+	suspending the PCM operations via
+	<function>snd_pcm_suspend_all()</function> or
+	<function>snd_pcm_suspend()</function>.  It means that the PCM
+	streams are already stoppped when the register snapshot is
+	taken.  But, remember that you don't have to restart the PCM
+	stream in the resume callback. It'll be restarted via 
+	trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant>
+	when necessary.
+    </para>
+
+    <para>
+      OK, we have all callbacks now. Let's set them up. In the
+      initialization of the card, make sure that you can get the chip
+      data from the card instance, typically via
+      <structfield>private_data</structfield> field, in case you
+      created the chip data individually.
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static int __devinit snd_mychip_probe(struct pci_dev *pci,
+                               const struct pci_device_id *pci_id)
+  {
+          ....
+          struct snd_card *card;
+          struct mychip *chip;
+          int err;
+          ....
+          err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
+          ....
+          chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+          ....
+          card->private_data = chip;
+          ....
+  }
+]]>
+        </programlisting>
+      </informalexample>
+
+	When you created the chip data with
+	<function>snd_card_create()</function>, it's anyway accessible
+	via <structfield>private_data</structfield> field.
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static int __devinit snd_mychip_probe(struct pci_dev *pci,
+                               const struct pci_device_id *pci_id)
+  {
+          ....
+          struct snd_card *card;
+          struct mychip *chip;
+          int err;
+          ....
+          err = snd_card_create(index[dev], id[dev], THIS_MODULE,
+                                sizeof(struct mychip), &card);
+          ....
+          chip = card->private_data;
+          ....
+  }
+]]>
+        </programlisting>
+      </informalexample>
+
+    </para>
+
+    <para>
+      If you need a space to save the registers, allocate the
+	buffer for it here, too, since it would be fatal
+    if you cannot allocate a memory in the suspend phase.
+    The allocated buffer should be released in the corresponding
+    destructor.
+    </para>
+
+    <para>
+      And next, set suspend/resume callbacks to the pci_driver.
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static struct pci_driver driver = {
+          .name = "My Chip",
+          .id_table = snd_my_ids,
+          .probe = snd_my_probe,
+          .remove = __devexit_p(snd_my_remove),
+  #ifdef CONFIG_PM
+          .suspend = snd_my_suspend,
+          .resume = snd_my_resume,
+  #endif
+  };
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Module Parameters  -->
+<!-- ****************************************************** -->
+  <chapter id="module-parameters">
+    <title>Module Parameters</title>
+    <para>
+      There are standard module options for ALSA. At least, each
+      module should have the <parameter>index</parameter>,
+      <parameter>id</parameter> and <parameter>enable</parameter>
+      options. 
+    </para>
+
+    <para>
+      If the module supports multiple cards (usually up to
+      8 = <constant>SNDRV_CARDS</constant> cards), they should be
+      arrays. The default initial values are defined already as
+      constants for easier programming:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
+  static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
+  static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+      If the module supports only a single card, they could be single
+    variables, instead.  <parameter>enable</parameter> option is not
+    always necessary in this case, but it would be better to have a
+    dummy option for compatibility.
+    </para>
+
+    <para>
+      The module parameters must be declared with the standard
+    <function>module_param()()</function>,
+    <function>module_param_array()()</function> and
+    <function>MODULE_PARM_DESC()</function> macros.
+    </para>
+
+    <para>
+      The typical coding would be like below:
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  #define CARD_NAME "My Chip"
+
+  module_param_array(index, int, NULL, 0444);
+  MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
+  module_param_array(id, charp, NULL, 0444);
+  MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
+  module_param_array(enable, bool, NULL, 0444);
+  MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+    <para>
+      Also, don't forget to define the module description, classes,
+      license and devices. Especially, the recent modprobe requires to
+      define the module license as GPL, etc., otherwise the system is
+      shown as <quote>tainted</quote>. 
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  MODULE_DESCRIPTION("My Chip");
+  MODULE_LICENSE("GPL");
+  MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
+]]>
+        </programlisting>
+      </informalexample>
+    </para>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- How To Put Your Driver  -->
+<!-- ****************************************************** -->
+  <chapter id="how-to-put-your-driver">
+    <title>How To Put Your Driver Into ALSA Tree</title>
+	<section>
+	<title>General</title>
+	<para>
+	So far, you've learned how to write the driver codes.
+	And you might have a question now: how to put my own
+	driver into the ALSA driver tree?
+	Here (finally :) the standard procedure is described briefly.
+	</para>
+
+	<para>
+	Suppose that you create a new PCI driver for the card
+	<quote>xyz</quote>.  The card module name would be
+	snd-xyz.  The new driver is usually put into the alsa-driver
+	tree, <filename>alsa-driver/pci</filename> directory in
+	the case of PCI cards.
+	Then the driver is evaluated, audited and tested
+	by developers and users.  After a certain time, the driver
+	will go to the alsa-kernel tree (to the corresponding directory,
+	such as <filename>alsa-kernel/pci</filename>) and eventually
+ 	will be integrated into the Linux 2.6 tree (the directory would be
+	<filename>linux/sound/pci</filename>).
+	</para>
+
+	<para>
+	In the following sections, the driver code is supposed
+	to be put into alsa-driver tree. The two cases are covered:
+	a driver consisting of a single source file and one consisting
+	of several source files.
+	</para>
+	</section>
+
+	<section>
+	<title>Driver with A Single Source File</title>
+	<para>
+	<orderedlist>
+	<listitem>
+	<para>
+	Modify alsa-driver/pci/Makefile
+	</para>
+
+	<para>
+	Suppose you have a file xyz.c.  Add the following
+	two lines
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  snd-xyz-objs := xyz.o
+  obj-$(CONFIG_SND_XYZ) += snd-xyz.o
+]]>
+        </programlisting>
+      </informalexample>
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	Create the Kconfig entry
+	</para>
+
+	<para>
+	Add the new entry of Kconfig for your xyz driver.
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  config SND_XYZ
+          tristate "Foobar XYZ"
+          depends on SND
+          select SND_PCM
+          help
+            Say Y here to include support for Foobar XYZ soundcard.
+
+            To compile this driver as a module, choose M here: the module
+            will be called snd-xyz.
+]]>
+        </programlisting>
+      </informalexample>
+
+	the line, select SND_PCM, specifies that the driver xyz supports
+	PCM.  In addition to SND_PCM, the following components are
+	supported for select command:
+	SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART,
+	SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC.
+	Add the select command for each supported component.
+	</para>
+
+	<para>
+	Note that some selections imply the lowlevel selections.
+	For example, PCM includes TIMER, MPU401_UART includes RAWMIDI,
+	AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP.
+	You don't need to give the lowlevel selections again.
+	</para>
+
+	<para>
+	For the details of Kconfig script, refer to the kbuild
+	documentation.
+	</para>
+
+	</listitem>
+
+	<listitem>
+	<para>
+	Run cvscompile script to re-generate the configure script and
+	build the whole stuff again.
+	</para>
+	</listitem>
+	</orderedlist>
+	</para>
+	</section>
+
+	<section>
+	<title>Drivers with Several Source Files</title>
+	<para>
+	Suppose that the driver snd-xyz have several source files.
+	They are located in the new subdirectory,
+	pci/xyz.
+
+	<orderedlist>
+	<listitem>
+	<para>
+	Add a new directory (<filename>xyz</filename>) in
+	<filename>alsa-driver/pci/Makefile</filename> as below
+
+      <informalexample>
+        <programlisting>
+<![CDATA[
+  obj-$(CONFIG_SND) += xyz/
+]]>
+        </programlisting>
+      </informalexample>
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	Under the directory <filename>xyz</filename>, create a Makefile
+
+      <example>
+	<title>Sample Makefile for a driver xyz</title>
+        <programlisting>
+<![CDATA[
+  ifndef SND_TOPDIR
+  SND_TOPDIR=../..
+  endif
+
+  include $(SND_TOPDIR)/toplevel.config
+  include $(SND_TOPDIR)/Makefile.conf
+
+  snd-xyz-objs := xyz.o abc.o def.o
+
+  obj-$(CONFIG_SND_XYZ) += snd-xyz.o
+
+  include $(SND_TOPDIR)/Rules.make
+]]>
+        </programlisting>
+      </example>
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	Create the Kconfig entry
+	</para>
+
+	<para>
+	This procedure is as same as in the last section.
+	</para>
+	</listitem>
+
+	<listitem>
+	<para>
+	Run cvscompile script to re-generate the configure script and
+	build the whole stuff again.
+	</para>
+	</listitem>
+	</orderedlist>
+	</para>
+	</section>
+
+  </chapter>
+
+<!-- ****************************************************** -->
+<!-- Useful Functions  -->
+<!-- ****************************************************** -->
+  <chapter id="useful-functions">
+    <title>Useful Functions</title>
+
+    <section id="useful-functions-snd-printk">
+      <title><function>snd_printk()</function> and friends</title>
+      <para>
+        ALSA provides a verbose version of the
+      <function>printk()</function> function. If a kernel config
+      <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this
+      function prints the given message together with the file name
+      and the line of the caller. The <constant>KERN_XXX</constant>
+      prefix is processed as 
+      well as the original <function>printk()</function> does, so it's
+      recommended to add this prefix, e.g. 
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n");
+]]>
+          </programlisting>
+        </informalexample>
+      </para>
+
+      <para>
+        There are also <function>printk()</function>'s for
+      debugging. <function>snd_printd()</function> can be used for
+      general debugging purposes. If
+      <constant>CONFIG_SND_DEBUG</constant> is set, this function is
+      compiled, and works just like
+      <function>snd_printk()</function>. If the ALSA is compiled
+      without the debugging flag, it's ignored. 
+      </para>
+
+      <para>
+        <function>snd_printdd()</function> is compiled in only when
+      <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note
+      that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default
+      even if you configure the alsa-driver with
+      <option>--with-debug=full</option> option. You need to give
+      explicitly <option>--with-debug=detect</option> option instead. 
+      </para>
+    </section>
+
+    <section id="useful-functions-snd-bug">
+      <title><function>snd_BUG()</function></title>
+      <para>
+        It shows the <computeroutput>BUG?</computeroutput> message and
+      stack trace as well as <function>snd_BUG_ON</function> at the point.
+      It's useful to show that a fatal error happens there. 
+      </para>
+      <para>
+	 When no debug flag is set, this macro is ignored. 
+      </para>
+    </section>
+
+    <section id="useful-functions-snd-bug-on">
+      <title><function>snd_BUG_ON()</function></title>
+      <para>
+        <function>snd_BUG_ON()</function> macro is similar with
+	<function>WARN_ON()</function> macro. For example,  
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_BUG_ON(!pointer);
+]]>
+          </programlisting>
+        </informalexample>
+
+	or it can be used as the condition,
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  if (snd_BUG_ON(non_zero_is_bug))
+          return -EINVAL;
+]]>
+          </programlisting>
+        </informalexample>
+
+      </para>
+
+      <para>
+        The macro takes an conditional expression to evaluate.
+	When <constant>CONFIG_SND_DEBUG</constant>, is set, the
+	expression is actually evaluated. If it's non-zero, it shows
+	the warning message such as
+	<computeroutput>BUG? (xxx)</computeroutput>
+	normally followed by stack trace.  It returns the evaluated
+	value.
+	When no <constant>CONFIG_SND_DEBUG</constant> is set, this
+	macro always returns zero.
+      </para>
+
+    </section>
+
+  </chapter>
+
+
+<!-- ****************************************************** -->
+<!-- Acknowledgments  -->
+<!-- ****************************************************** -->
+  <chapter id="acknowledgments">
+    <title>Acknowledgments</title>
+    <para>
+      I would like to thank Phil Kerr for his help for improvement and
+      corrections of this document. 
+    </para>
+    <para>
+    Kevin Conder reformatted the original plain-text to the
+    DocBook format.
+    </para>
+    <para>
+    Giuliano Pochini corrected typos and contributed the example codes
+    in the hardware constraints section.
+    </para>
+  </chapter>
+</book>