Documentation/usb/gadget-testing.rst
This file summarizes information on basic testing of USB functions provided by gadgets.
.. contents
ACM function
ECM function
ECM subset function
EEM function
FFS function
HID function
LOOPBACK function
MASS STORAGE function
MIDI function
NCM function
OBEX function
PHONET function
RNDIS function
SERIAL function
SOURCESINK function
UAC1 function (legacy implementation)
UAC2 function
UVC function
PRINTER function
UAC1 function (new API)
MIDI2 function
ACM function ===============
The function is provided by usb_f_acm.ko module.
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.
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>
The function is provided by usb_f_ecm.ko module.
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. The ifname can be written to if the function is not bound. A write must be an interface pattern such as "usb%d", which will cause the net core to choose the next free usbX interface. By default, it is set to "usb%d".
Configure IP addresses of the device and the host. Then:
On the device::
ping <host's IP>
On the host::
ping <device's IP>
The function is provided by usb_f_ecm_subset.ko module.
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. The ifname can be written to if the function is not bound. A write must be an interface pattern such as "usb%d", which will cause the net core to choose the next free usbX interface. By default, it is set to "usb%d".
Configure IP addresses of the device and the host. Then:
On the device::
ping <host's IP>
On the host::
ping <device's IP>
The function is provided by usb_f_eem.ko module.
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. The ifname can be written to if the function is not bound. A write must be an interface pattern such as "usb%d", which will cause the net core to choose the next free usbX interface. By default, it is set to "usb%d".
Configure IP addresses of the device and the host. Then:
On the device::
ping <host's IP>
On the host::
ping <device's IP>
The function is provided by usb_f_fs.ko module.
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.
The FFS function provides just one attribute in its function directory:
ready
The attribute is read-only and signals if the function is ready (1) to be used, E.G. if userspace has written descriptors and strings to ep0, so the gadget can be enabled.
On the device: start the function's userspace daemon, enable the gadget
On the host: use the USB function provided by the device
The function is provided by usb_f_hid.ko module.
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.....
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:
The function is provided by usb_f_ss_lb.ko module.
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
=============== =======================
device: run the gadget
host: test-usb (tools/usb/testusb.c)
The function is provided by usb_f_mass_storage.ko module.
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)
forced_eject This write-only file is useful only when
the function is active. It causes the backing
file to be forcibly detached from the LUN,
regardless of whether the host has allowed it.
Any non-zero number of bytes written will
result in ejection.
=============== ==============================================
device: connect the gadget, enable it host: dmesg, see the USB drives appear (if system configured to automatically mount)
The function is provided by usb_f_midi.ko module.
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
interface_string USB AudioControl interface string
================ ====================================
There are two cases: playing a mid from the gadget to the host and playing a mid from the host to the gadget.
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
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.
The function is provided by usb_f_ncm.ko module.
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
max_segment_size Segment size required for P2P connections. This
will set MTU to 14 bytes
======================= ==================================================
and after creating the functions/ncm.<instance name> they contain default values: qmult is 5, dev_addr and host_addr are randomly selected. The ifname can be written to if the function is not bound. A write must be an interface pattern such as "usb%d", which will cause the net core to choose the next free usbX interface. By default, it is set to "usb%d".
Configure IP addresses of the device and the host. Then:
On the device::
ping <host's IP>
On the host::
ping <device's IP>
The function is provided by usb_f_obex.ko module.
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.
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:
https://github.com/felipebalbi/usb-tools.git master
The function is provided by usb_f_phonet.ko module.
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
=============== ==================================================
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
The function is provided by usb_f_rndis.ko module.
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. The ifname can be written to if the function is not bound. A write must be an interface pattern such as "usb%d", which will cause the net core to choose the next free usbX interface. By default, it is set to "usb%d".
Configure IP addresses of the device and the host. Then:
On the device::
ping <host's IP>
On the host::
ping <device's IP>
The function is provided by usb_f_gser.ko module.
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.
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>
The function is provided by usb_f_ss_lb.ko module.
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_maxburst 0..15 (ss only)
bulk_qlen depth of queue for bulk
iso_qlen depth of queue for iso
=============== ==================================
device: run the gadget
host: test-usb (tools/usb/testusb.c)
The function is provided by usb_f_uac1_legacy.ko module.
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.
device: run the gadget
host::
aplay -l # should list our USB Audio Gadget
The function is provided by usb_f_uac2.ko module.
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 list of capture sampling rates (comma-separated)
c_ssize capture sample size (bytes)
c_sync capture synchronization type (async/adaptive)
c_mute_present capture mute control enable
c_volume_present capture volume control enable
c_volume_min capture volume control min value (in 1/256 dB)
c_volume_max capture volume control max value (in 1/256 dB)
c_volume_res capture volume control resolution (in 1/256 dB)
c_hs_bint capture bInterval for HS/SS (1-4: fixed, 0: auto)
fb_max maximum extra bandwidth in async mode
p_chmask playback channel mask
p_srate list of playback sampling rates (comma-separated)
p_ssize playback sample size (bytes)
p_mute_present playback mute control enable
p_volume_present playback volume control enable
p_volume_min playback volume control min value (in 1/256 dB)
p_volume_max playback volume control max value (in 1/256 dB)
p_volume_res playback volume control resolution (in 1/256 dB)
p_hs_bint playback bInterval for HS/SS (1-4: fixed, 0: auto)
req_number the number of pre-allocated request for both capture
and playback
function_name name of the interface
if_ctrl_name topology control name
clksrc_in_name input clock name
clksrc_out_name output clock name
p_it_name playback input terminal name
p_it_ch_name playback input first channel name
p_ot_name playback output terminal name
p_fu_vol_name playback function unit name
c_it_name capture input terminal name
c_it_ch_name capture input first channel name
c_ot_name capture output terminal name
c_fu_vol_name capture functional unit name
c_terminal_type code of the capture terminal type
p_terminal_type code of the playback terminal type
================ ====================================================
The attributes have sane default values.
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
The function is provided by usb_f_uvc.ko module.
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
function_name name of the interface
=================== ================================================
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 interval value in each line. The rules stated above are best illustrated with an example::
666666 1000000 5000000 EOF
device: run the gadget, modprobe vivid::
where uvc-gadget is this program: http://git.ideasonboard.org/uvc-gadget.git
with these patches:
https://lore.kernel.org/r/[email protected]/
host::
luvcview -f yuv
The function is provided by usb_f_printer.ko module.
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
========== ===========================================
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.
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.
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 list of capture sampling rates (comma-separated)
c_ssize capture sample size (bytes)
c_mute_present capture mute control enable
c_volume_present capture volume control enable
c_volume_min capture volume control min value (in 1/256 dB)
c_volume_max capture volume control max value (in 1/256 dB)
c_volume_res capture volume control resolution (in 1/256 dB)
p_chmask playback channel mask
p_srate list of playback sampling rates (comma-separated)
p_ssize playback sample size (bytes)
p_mute_present playback mute control enable
p_volume_present playback volume control enable
p_volume_min playback volume control min value (in 1/256 dB)
p_volume_max playback volume control max value (in 1/256 dB)
p_volume_res playback volume control resolution (in 1/256 dB)
req_number the number of pre-allocated requests for both capture
and playback
function_name name of the interface
p_it_name playback input terminal name
p_it_ch_name playback channels name
p_ot_name playback output terminal name
p_fu_vol_name playback mute/volume functional unit name
c_it_name capture input terminal name
c_it_ch_name capture channels name
c_ot_name capture output terminal name
c_fu_vol_name capture mute/volume functional unit name
================ ====================================================
The attributes have sane default values.
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
The function is provided by usb_f_midi2.ko module. It will create a virtual ALSA card containing a UMP rawmidi device where the UMP packet is looped back. In addition, a legacy rawmidi device is created. The UMP rawmidi is bound with ALSA sequencer clients, too.
The function name to use when creating the function directory is "midi2". The midi2 function provides these attributes in its function directory as the card top-level information:
============= =================================================
process_ump Bool flag to process UMP Stream messages (0 or 1)
static_block Bool flag for static blocks (0 or 1)
iface_name Optional interface name string
============= =================================================
The directory contains a subdirectory "ep.0", and this provides the attributes for a UMP Endpoint (which is a pair of USB MIDI Endpoints):
============= =================================================
protocol_caps MIDI protocol capabilities;
1: MIDI 1.0, 2: MIDI 2.0, or 3: both protocols
protocol Default MIDI protocol (either 1 or 2)
ep_name UMP Endpoint name string
product_id Product ID string
manufacturer Manufacture ID number (24 bit)
family Device family ID number (16 bit)
model Device model ID number (16 bit)
sw_revision Software revision (32 bit)
============= =================================================
Each Endpoint subdirectory contains a subdirectory "block.0", which represents the Function Block for Block 0 information. Its attributes are:
================= ===============================================
name Function Block name string
direction Direction of this FB
1: input, 2: output, or 3: bidirectional
first_group The first UMP Group number (0-15)
num_groups The number of groups in this FB (1-16)
midi1_first_group The first UMP Group number for MIDI 1.0 (0-15)
midi1_num_groups The number of groups for MIDI 1.0 (0-16)
ui_hint UI-hint of this FB
0: unknown, 1: receiver, 2: sender, 3: both
midi_ci_version Supported MIDI-CI version number (8 bit)
is_midi1 Legacy MIDI 1.0 device (0-2)
0: MIDI 2.0 device,
1: MIDI 1.0 without restriction, or
2: MIDI 1.0 with low speed
sysex8_streams Max number of SysEx8 streams (8 bit)
active Bool flag for FB activity (0 or 1)
================= ===============================================
If multiple Function Blocks are required, you can add more Function Blocks by creating subdirectories "block.<num>" with the corresponding Function Block number (1, 2, ....). The FB subdirectories can be dynamically removed, too. Note that the Function Block numbers must be continuous.
Similarly, if you multiple UMP Endpoints are required, you can add more Endpoints by creating subdirectories "ep.<num>". The number must be continuous.
For emulating the old MIDI 2.0 device without UMP v1.1 support, pass 0
to process_ump flag. Then the whole UMP v1.1 requests are ignored.
On the device: run the gadget, and running::
$ cat /proc/asound/cards
will show a new sound card containing a MIDI2 device.
OTOH, on the host::
$ cat /proc/asound/cards
will show a new sound card containing either MIDI1 or MIDI2 device, depending on the USB audio driver configuration.
On both, when ALSA sequencer is enabled on the host, you can find the UMP MIDI client such as "MIDI 2.0 Gadget".
As the driver simply loops back the data, there is no need for a real device just for testing.
For testing a MIDI input from the gadget to the host (e.g. emulating a MIDI keyboard), you can send a MIDI stream like the following.
On the gadget::
$ aconnect -o .... client 20: 'MIDI 2.0 Gadget' [type=kernel,card=1] 0 'MIDI 2.0 ' 1 'Group 1 (MIDI 2.0 Gadget I/O)' $ aplaymidi -p 20:1 to_host.mid
On the host::
$ aconnect -i .... client 24: 'MIDI 2.0 Gadget' [type=kernel,card=2] 0 'MIDI 2.0 ' 1 'Group 1 (MIDI 2.0 Gadget I/O)' $ arecordmidi -p 24:1 from_gadget.mid
If you have a UMP-capable application, you can use the UMP port to send/receive the raw UMP packets, too. For example, aseqdump program with UMP support can receive from UMP port. On the host::
$ aseqdump -u 2 -p 24:1 Waiting for data. Press Ctrl+C to end. Source Group Event Ch Data 24:1 Group 0, Program change 0, program 0, Bank select 0:0 24:1 Group 0, Channel pressure 0, value 0x80000000
For testing a MIDI output to the gadget to the host (e.g. emulating a MIDI synth), it'll be just other way round.
On the gadget::
$ arecordmidi -p 20:1 from_host.mid
On the host::
$ aplaymidi -p 24:1 to_gadget.mid
The access to MIDI 1.0 on altset 0 on the host is supported, and it's translated from/to UMP packets on the gadget. It's bound to only Function Block 0.
The current operation mode can be observed in ALSA control element "Operation Mode" for SND_CTL_IFACE_RAWMIDI. For example::
$ amixer -c1 contents numid=1,iface=RAWMIDI,name='Operation Mode' ; type=INTEGER,access=r--v----,values=1,min=0,max=2,step=0 : values=2
where 0 = unused, 1 = MIDI 1.0 (altset 0), 2 = MIDI 2.0 (altset 1). The example above shows it's running in 2, i.e. MIDI 2.0.