WSL2-Linux-Kernel/Documentation/usb/gadget-testing.txt

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
7. LOOPBACK function
8. MASS STORAGE function
9. MIDI 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

7. LOOPBACK function
====================

The function is provided by usb_f_ss_lb.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "Loopback".
The LOOPBACK function provides these attributes in its function directory:

	qlen		- depth of loopback queue
	bulk_buflen	- buffer length

Testing the LOOPBACK function
-----------------------------

device: run the gadget
host: test-usb

http://www.linux-usb.org/usbtest/testusb.c

8. MASS STORAGE function
========================

The function is provided by usb_f_mass_storage.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "mass_storage".
The MASS STORAGE function provides these attributes in its directory:
files:

	stall		- Set to permit function to halt bulk endpoints.
			Disabled on some USB devices known not to work
			correctly. You should set it to true.
	num_buffers	- Number of pipeline buffers. Valid numbers
			are 2..4. Available only if
			CONFIG_USB_GADGET_DEBUG_FILES is set.

and a default lun.0 directory corresponding to SCSI LUN #0.

A new lun can be added with mkdir:

$ mkdir functions/mass_storage.0/partition.5

Lun numbering does not have to be continuous, except for lun #0 which is
created by default. A maximum of 8 luns can be specified and they all must be
named following the <name>.<number> scheme. The numbers can be 0..8.
Probably a good convention is to name the luns "lun.<number>",
although it is not mandatory.

In each lun directory there are the following attribute files:

	file		- The path to the backing file for the LUN.
			Required if LUN is not marked as removable.
	ro		- Flag specifying access to the LUN shall be
			read-only. This is implied if CD-ROM emulation
			is enabled as well as when it was impossible
			to open "filename" in R/W mode.
	removable	- Flag specifying that LUN shall be indicated as
			being removable.
	cdrom		- Flag specifying that LUN shall be reported as
			being a CD-ROM.
	nofua		- Flag specifying that FUA flag
			in SCSI WRITE(10,12)

Testing the MASS STORAGE function
---------------------------------

device: connect the gadget, enable it
host: dmesg, see the USB drives appear (if system configured to automatically
mount)

9. MIDI function
================

The function is provided by usb_f_midi.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "midi".
The MIDI function provides these attributes in its function directory:

	buflen		- MIDI buffer length
	id		- ID string for the USB MIDI adapter
	in_ports	- number of MIDI input ports
	index		- index value for the USB MIDI adapter
	out_ports	- number of MIDI output ports
	qlen		- USB read request queue length

Testing the MIDI function
-------------------------

There are two cases: playing a mid from the gadget to
the host and playing a mid from the host to the gadget.

1) Playing a mid from the gadget to the host
host)

$ arecordmidi -l
 Port    Client name                      Port name
 14:0    Midi Through                     Midi Through Port-0
 24:0    MIDI Gadget                      MIDI Gadget MIDI 1
$ arecordmidi -p 24:0 from_gadget.mid

gadget)

$ aplaymidi -l
 Port    Client name                      Port name
 20:0    f_midi                           f_midi

$ aplaymidi -p 20:0 to_host.mid

2) Playing a mid from the host to the gadget
gadget)

$ arecordmidi -l
 Port    Client name                      Port name
 20:0    f_midi                           f_midi

$ arecordmidi -p 20:0 from_host.mid

host)

$ aplaymidi -l
 Port    Client name                      Port name
 14:0    Midi Through                     Midi Through Port-0
 24:0    MIDI Gadget                      MIDI Gadget MIDI 1

$ aplaymidi -p24:0 to_gadget.mid

The from_gadget.mid should sound identical to the to_host.mid.
The from_host.id should sound identical to the to_gadget.mid.

MIDI files can be played to speakers/headphones with e.g. timidity installed

$ aplaymidi -l
 Port    Client name                      Port name
 14:0    Midi Through                     Midi Through Port-0
 24:0    MIDI Gadget                      MIDI Gadget MIDI 1
128:0    TiMidity                         TiMidity port 0
128:1    TiMidity                         TiMidity port 1
128:2    TiMidity                         TiMidity port 2
128:3    TiMidity                         TiMidity port 3

$ aplaymidi -p 128:0 file.mid

MIDI ports can be logically connected using the aconnect utility, e.g.:

$ aconnect 24:0 128:0 # try it on the host

After the gadget's MIDI port is connected to timidity's MIDI port,
whatever is played at the gadget side with aplaymidi -l is audible
in host's speakers/headphones.