Gadget Testing

This file summarizes information on basic testing of USB functions provided by gadgets.

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.rst:

    $ ./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 (tools/usb/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
  1. 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.

10. NCM function

The function is provided by usb_f_ncm.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “ncm”. The NCM 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/ncm.<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 NCM 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>

11. OBEX function

The function is provided by usb_f_obex.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “obex”. The OBEX 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 OBEX function

On device:

seriald -f /dev/ttyGS<Y> -s 1024

On host:

serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
        -t<out endpoint addr> -r<in endpoint addr>

where seriald and serialc are Felipe’s utilities found here:

12. PHONET function

The function is provided by usb_f_phonet.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “phonet”. The PHONET function provides just one attribute in its function directory:

ifname network device interface name associated with this function instance

Testing the PHONET function

It is not possible to test the SOCK_STREAM protocol without a specific piece of hardware, so only SOCK_DGRAM has been tested. For the latter to work, in the past I had to apply the patch mentioned here:

http://www.spinics.net/lists/linux-usb/msg85689.html

These tools are required:

git://git.gitorious.org/meego-cellular/phonet-utils.git

On the host:

$ ./phonet -a 0x10 -i usbpn0
$ ./pnroute add 0x6c usbpn0
$./pnroute add 0x10 usbpn0
$ ifconfig usbpn0 up

On the device:

$ ./phonet -a 0x6c -i upnlink0
$ ./pnroute add 0x10 upnlink0
$ ifconfig upnlink0 up

Then a test program can be used:

http://www.spinics.net/lists/linux-usb/msg85690.html

On the device:

$ ./pnxmit -a 0x6c -r

On the host:

$ ./pnxmit -a 0x10 -s 0x6c

As a result some data should be sent from host to device. Then the other way round:

On the host:

$ ./pnxmit -a 0x10 -r

On the device:

$ ./pnxmit -a 0x6c -s 0x10

13. RNDIS function

The function is provided by usb_f_rndis.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “rndis”. The RNDIS 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/rndis.<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 RNDIS 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>

14. SERIAL function

The function is provided by usb_f_gser.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “gser”. The SERIAL 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 SERIAL function

On host:

insmod usbserial
echo VID PID >/sys/bus/usb-serial/drivers/generic/new_id

On host:

cat > /dev/ttyUSB<X>

On target:

cat /dev/ttyGS<Y>

then the other way round

On target:

cat > /dev/ttyGS<Y>

On host:

cat /dev/ttyUSB<X>

15. SOURCESINK 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 “SourceSink”. The SOURCESINK function provides these attributes in its function directory:

pattern 0 (all zeros), 1 (mod63), 2 (none)
isoc_interval 1..16
isoc_maxpacket 0 - 1023 (fs), 0 - 1024 (hs/ss)
isoc_mult 0..2 (hs/ss only)
isoc_maxburst 0..15 (ss only)
bulk_buflen buffer length
bulk_qlen depth of queue for bulk
iso_qlen depth of queue for iso

Testing the SOURCESINK function

device: run the gadget

host: test-usb (tools/usb/testusb.c)

16. UAC1 function (legacy implementation)

The function is provided by usb_f_uac1_legacy.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “uac1_legacy”. The uac1 function provides these attributes in its function directory:

audio_buf_size audio buffer size
fn_cap capture pcm device file name
fn_cntl control device file name
fn_play playback pcm device file name
req_buf_size ISO OUT endpoint request buffer size
req_count ISO OUT endpoint request count

The attributes have sane default values.

Testing the UAC1 function

device: run the gadget

host:

aplay -l # should list our USB Audio Gadget

17. UAC2 function

The function is provided by usb_f_uac2.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “uac2”. The uac2 function provides these attributes in its function directory:

c_chmask capture channel mask
c_srate capture sampling rate
c_ssize capture sample size (bytes)
p_chmask playback channel mask
p_srate playback sampling rate
p_ssize playback sample size (bytes)
req_number the number of pre-allocated request for both capture and playback

The attributes have sane default values.

Testing the UAC2 function

device: run the gadget host: aplay -l # should list our USB Audio Gadget

This function does not require real hardware support, it just sends a stream of audio data to/from the host. In order to actually hear something at the device side, a command similar to this must be used at the device side:

$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &

e.g.:

$ arecord -f dat -t wav -D hw:CARD=UAC2Gadget,DEV=0 | \
  aplay -D default:CARD=OdroidU3

18. UVC function

The function is provided by usb_f_uvc.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “uvc”. The uvc function provides these attributes in its function directory:

streaming_interval interval for polling endpoint for data transfers
streaming_maxburst bMaxBurst for super speed companion descriptor
streaming_maxpacket maximum packet size this endpoint is capable of sending or receiving when this configuration is selected

There are also “control” and “streaming” subdirectories, each of which contain a number of their subdirectories. There are some sane defaults provided, but the user must provide the following:

control header create in control/header, link from control/class/fs and/or control/class/ss
streaming header create in streaming/header, link from streaming/class/fs and/or streaming/class/hs and/or streaming/class/ss
format description create in streaming/mjpeg and/or streaming/uncompressed
frame description create in streaming/mjpeg/<format> and/or in streaming/uncompressed/<format>

Each frame description contains frame interval specification, and each such specification consists of a number of lines with an inverval value in each line. The rules stated above are best illustrated with an example:

# mkdir functions/uvc.usb0/control/header/h
# cd functions/uvc.usb0/control/
# ln -s header/h class/fs
# ln -s header/h class/ss
# mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
# cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/360p/dwFrameInterval
666666
1000000
5000000
EOF
# cd $GADGET_CONFIGFS_ROOT
# mkdir functions/uvc.usb0/streaming/header/h
# cd functions/uvc.usb0/streaming/header/h
# ln -s ../../uncompressed/u
# cd ../../class/fs
# ln -s ../../header/h
# cd ../../class/hs
# ln -s ../../header/h
# cd ../../class/ss
# ln -s ../../header/h

Testing the UVC function

device: run the gadget, modprobe vivid:

# uvc-gadget -u /dev/video<uvc video node #> -v /dev/video<vivid video node #>
where uvc-gadget is this program:
http://git.ideasonboard.org/uvc-gadget.git

with these patches:

host:

luvcview -f yuv

19. PRINTER function

The function is provided by usb_f_printer.ko module.

Function-specific configfs interface

The function name to use when creating the function directory is “printer”. The printer function provides these attributes in its function directory:

pnp_string Data to be passed to the host in pnp string
q_len Number of requests per endpoint

Testing the PRINTER function

The most basic testing:

device: run the gadget:

# ls -l /devices/virtual/usb_printer_gadget/

should show g_printer<number>.

If udev is active, then /dev/g_printer<number> should appear automatically.

host:

If udev is active, then e.g. /dev/usb/lp0 should appear.

host->device transmission:

device:

# cat /dev/g_printer<number>

host:

# cat > /dev/usb/lp0

device->host transmission:

# cat > /dev/g_printer<number>

host:

# cat /dev/usb/lp0

More advanced testing can be done with the prn_example described in Documentation/usb/gadget_printer.rst.

20. UAC1 function (virtual ALSA card, using u_audio API)

The function is provided by usb_f_uac1.ko module. It will create a virtual ALSA card and the audio streams are simply sinked to and sourced from it.

Function-specific configfs interface

The function name to use when creating the function directory is “uac1”. The uac1 function provides these attributes in its function directory:

c_chmask capture channel mask
c_srate capture sampling rate
c_ssize capture sample size (bytes)
p_chmask playback channel mask
p_srate playback sampling rate
p_ssize playback sample size (bytes)
req_number the number of pre-allocated request for both capture and playback

The attributes have sane default values.

Testing the UAC1 function

device: run the gadget host: aplay -l # should list our USB Audio Gadget

This function does not require real hardware support, it just sends a stream of audio data to/from the host. In order to actually hear something at the device side, a command similar to this must be used at the device side:

$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &

e.g.:

$ arecord -f dat -t wav -D hw:CARD=UAC1Gadget,DEV=0 | \
  aplay -D default:CARD=OdroidU3