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This file summarizes information on basic testing of USB functions
provided by gadgets.
1. ACM function
2. ECM function
3. ECM subset function
4. EEM function
5. FFS function
6. HID function
1. ACM function
===============
The function is provided by usb_f_acm.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "acm".
The ACM function provides just one attribute in its function directory:
port_num
The attribute is read-only.
There can be at most 4 ACM/generic serial/OBEX ports in the system.
Testing the ACM function
------------------------
On the host: cat > /dev/ttyACM<X>
On the device : cat /dev/ttyGS<Y>
then the other way round
On the device: cat > /dev/ttyGS<Y>
On the host: cat /dev/ttyACM<X>
2. ECM function
===============
The function is provided by usb_f_ecm.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "ecm".
The ECM function provides these attributes in its function directory:
ifname - network device interface name associated with this
function instance
qmult - queue length multiplier for high and super speed
host_addr - MAC address of host's end of this
Ethernet over USB link
dev_addr - MAC address of device's end of this
Ethernet over USB link
and after creating the functions/ecm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
Except for ifname they can be written to until the function is linked to a
configuration. The ifname is read-only and contains the name of the interface
which was assigned by the net core, e. g. usb0.
Testing the ECM function
------------------------
Configure IP addresses of the device and the host. Then:
On the device: ping <host's IP>
On the host: ping <device's IP>
3. ECM subset function
======================
The function is provided by usb_f_ecm_subset.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "geth".
The ECM subset function provides these attributes in its function directory:
ifname - network device interface name associated with this
function instance
qmult - queue length multiplier for high and super speed
host_addr - MAC address of host's end of this
Ethernet over USB link
dev_addr - MAC address of device's end of this
Ethernet over USB link
and after creating the functions/ecm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
Except for ifname they can be written to until the function is linked to a
configuration. The ifname is read-only and contains the name of the interface
which was assigned by the net core, e. g. usb0.
Testing the ECM subset function
-------------------------------
Configure IP addresses of the device and the host. Then:
On the device: ping <host's IP>
On the host: ping <device's IP>
4. EEM function
===============
The function is provided by usb_f_eem.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "eem".
The EEM function provides these attributes in its function directory:
ifname - network device interface name associated with this
function instance
qmult - queue length multiplier for high and super speed
host_addr - MAC address of host's end of this
Ethernet over USB link
dev_addr - MAC address of device's end of this
Ethernet over USB link
and after creating the functions/eem.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
Except for ifname they can be written to until the function is linked to a
configuration. The ifname is read-only and contains the name of the interface
which was assigned by the net core, e. g. usb0.
Testing the EEM function
------------------------
Configure IP addresses of the device and the host. Then:
On the device: ping <host's IP>
On the host: ping <device's IP>
5. FFS function
===============
The function is provided by usb_f_fs.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "ffs".
The function directory is intentionally empty and not modifiable.
After creating the directory there is a new instance (a "device") of FunctionFS
available in the system. Once a "device" is available, the user should follow
the standard procedure for using FunctionFS (mount it, run the userspace
process which implements the function proper). The gadget should be enabled
by writing a suitable string to usb_gadget/<gadget>/UDC.
Testing the FFS function
------------------------
On the device: start the function's userspace daemon, enable the gadget
On the host: use the USB function provided by the device
6. HID function
===============
The function is provided by usb_f_hid.ko module.
Function-specific configfs interface
------------------------------------
The function name to use when creating the function directory is "hid".
The HID function provides these attributes in its function directory:
protocol - HID protocol to use
report_desc - data to be used in HID reports, except data
passed with /dev/hidg<X>
report_length - HID report length
subclass - HID subclass to use
For a keyboard the protocol and the subclass are 1, the report_length is 8,
while the report_desc is:
$ hd my_report_desc
00000000 05 01 09 06 a1 01 05 07 19 e0 29 e7 15 00 25 01 |..........)...%.|
00000010 75 01 95 08 81 02 95 01 75 08 81 03 95 05 75 01 |u.......u.....u.|
00000020 05 08 19 01 29 05 91 02 95 01 75 03 91 03 95 06 |....).....u.....|
00000030 75 08 15 00 25 65 05 07 19 00 29 65 81 00 c0 |u...%e....)e...|
0000003f
Such a sequence of bytes can be stored to the attribute with echo:
$ echo -ne \\x05\\x01\\x09\\x06\\xa1.....
Testing the HID function
------------------------
Device:
- create the gadget
- connect the gadget to a host, preferably not the one used
to control the gadget
- run a program which writes to /dev/hidg<N>, e.g.
a userspace program found in Documentation/usb/gadget_hid.txt:
$ ./hid_gadget_test /dev/hidg0 keyboard
Host:
- observe the keystrokes from the gadget
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