diff options
Diffstat (limited to 'Documentation/ide/ide-tape.txt')
| -rw-r--r-- | Documentation/ide/ide-tape.txt | 132 |
1 files changed, 65 insertions, 67 deletions
diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt index 51f596b282cd..3f348a0b21d8 100644 --- a/Documentation/ide/ide-tape.txt +++ b/Documentation/ide/ide-tape.txt @@ -1,67 +1,65 @@ -/* - * IDE ATAPI streaming tape driver. - * - * This driver is a part of the Linux ide driver. - * - * The driver, in co-operation with ide.c, basically traverses the - * request-list for the block device interface. The character device - * interface, on the other hand, creates new requests, adds them - * to the request-list of the block device, and waits for their completion. - * - * The block device major and minor numbers are determined from the - * tape's relative position in the ide interfaces, as explained in ide.c. - * - * The character device interface consists of the following devices: - * - * ht0 major 37, minor 0 first IDE tape, rewind on close. - * ht1 major 37, minor 1 second IDE tape, rewind on close. - * ... - * nht0 major 37, minor 128 first IDE tape, no rewind on close. - * nht1 major 37, minor 129 second IDE tape, no rewind on close. - * ... - * - * The general magnetic tape commands compatible interface, as defined by - * include/linux/mtio.h, is accessible through the character device. - * - * General ide driver configuration options, such as the interrupt-unmask - * flag, can be configured by issuing an ioctl to the block device interface, - * as any other ide device. - * - * Our own ide-tape ioctl's can be issued to either the block device or - * the character device interface. - * - * Maximal throughput with minimal bus load will usually be achieved in the - * following scenario: - * - * 1. ide-tape is operating in the pipelined operation mode. - * 2. No buffering is performed by the user backup program. - * - * Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive. - * - * Here are some words from the first releases of hd.c, which are quoted - * in ide.c and apply here as well: - * - * | Special care is recommended. Have Fun! - * - * Possible improvements. - * - * 1. Support for the ATAPI overlap protocol. - * - * In order to maximize bus throughput, we currently use the DSC - * overlap method which enables ide.c to service requests from the - * other device while the tape is busy executing a command. The - * DSC overlap method involves polling the tape's status register - * for the DSC bit, and servicing the other device while the tape - * isn't ready. - * - * In the current QIC development standard (December 1995), - * it is recommended that new tape drives will *in addition* - * implement the ATAPI overlap protocol, which is used for the - * same purpose - efficient use of the IDE bus, but is interrupt - * driven and thus has much less CPU overhead. - * - * ATAPI overlap is likely to be supported in most new ATAPI - * devices, including new ATAPI cdroms, and thus provides us - * a method by which we can achieve higher throughput when - * sharing a (fast) ATA-2 disk with any (slow) new ATAPI device. - */ +IDE ATAPI streaming tape driver. + +This driver is a part of the Linux ide driver. + +The driver, in co-operation with ide.c, basically traverses the +request-list for the block device interface. The character device +interface, on the other hand, creates new requests, adds them +to the request-list of the block device, and waits for their completion. + +The block device major and minor numbers are determined from the +tape's relative position in the ide interfaces, as explained in ide.c. + +The character device interface consists of the following devices: + +ht0 major 37, minor 0 first IDE tape, rewind on close. +ht1 major 37, minor 1 second IDE tape, rewind on close. +... +nht0 major 37, minor 128 first IDE tape, no rewind on close. +nht1 major 37, minor 129 second IDE tape, no rewind on close. +... + +The general magnetic tape commands compatible interface, as defined by +include/linux/mtio.h, is accessible through the character device. + +General ide driver configuration options, such as the interrupt-unmask +flag, can be configured by issuing an ioctl to the block device interface, +as any other ide device. + +Our own ide-tape ioctl's can be issued to either the block device or +the character device interface. + +Maximal throughput with minimal bus load will usually be achieved in the +following scenario: + + 1. ide-tape is operating in the pipelined operation mode. + 2. No buffering is performed by the user backup program. + +Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive. + +Here are some words from the first releases of hd.c, which are quoted +in ide.c and apply here as well: + +| Special care is recommended. Have Fun! + +Possible improvements: + +1. Support for the ATAPI overlap protocol. + +In order to maximize bus throughput, we currently use the DSC +overlap method which enables ide.c to service requests from the +other device while the tape is busy executing a command. The +DSC overlap method involves polling the tape's status register +for the DSC bit, and servicing the other device while the tape +isn't ready. + +In the current QIC development standard (December 1995), +it is recommended that new tape drives will *in addition* +implement the ATAPI overlap protocol, which is used for the +same purpose - efficient use of the IDE bus, but is interrupt +driven and thus has much less CPU overhead. + +ATAPI overlap is likely to be supported in most new ATAPI +devices, including new ATAPI cdroms, and thus provides us +a method by which we can achieve higher throughput when +sharing a (fast) ATA-2 disk with any (slow) new ATAPI device. |