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>

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 thisfunction instance
qmult	queue length multiplier for high and super speed
host_addr	MAC address of host’s end of thisEthernet over USB link
dev_addr	MAC address of device’s end of thisEthernet over USB link

and after creating the functions/ecm.<instance name> they contain defaultvalues: 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 aconfiguration. The ifname is read-only and contains the name of the interfacewhich 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>

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 thisfunction instance
qmult	queue length multiplier for high and super speed
host_addr	MAC address of host’s end of thisEthernet over USB link
dev_addr	MAC address of device’s end of thisEthernet over USB link

and after creating the functions/ecm.<instance name> they contain defaultvalues: 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 aconfiguration. The ifname is read-only and contains the name of the interfacewhich 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>

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 thisfunction instance
qmult	queue length multiplier for high and super speed
host_addr	MAC address of host’s end of thisEthernet over USB link
dev_addr	MAC address of device’s end of thisEthernet over USB link

and after creating the functions/eem.<instance name> they contain defaultvalues: 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 aconfiguration. The ifname is read-only and contains the name of the interfacewhich 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>

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 FunctionFSavailable in the system. Once a “device” is available, the user should followthe standard procedure for using FunctionFS (mount it, run the userspaceprocess which implements the function proper). The gadget should be enabledby 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

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 datapassed 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_desc00000000  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 usedto 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

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)

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 workcorrectly. You should set it to true.
num_buffers	Number of pipeline buffers. Valid numbersare 2..4. Available only ifCONFIG_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 iscreated by default. A maximum of 8 luns can be specified and they all must benamed 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 beread-only. This is implied if CD-ROM emulationis enabled as well as when it was impossibleto open “filename” in R/W mode.
removable	Flag specifying that LUN shall be indicated asbeing removable.
cdrom	Flag specifying that LUN shall be reported asbeing a CD-ROM.
nofua	Flag specifying that FUA flagin SCSI WRITE(10,12)

Testing the MASS STORAGE function¶

device: connect the gadget, enable ithost: dmesg, see the USB drives appear (if system configured to automaticallymount)

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 tothe 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 1128:0    TiMidity                         TiMidity port 0128:1    TiMidity                         TiMidity port 1128:2    TiMidity                         TiMidity port 2128:3    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 audiblein host’s speakers/headphones.

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 thisfunction instance
qmult	queue length multiplier for high and super speed
host_addr	MAC address of host’s end of thisEthernet over USB link
dev_addr	MAC address of device’s end of thisEthernet over USB link

and after creating the functions/ncm.<instance name> they contain defaultvalues: 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 aconfiguration. The ifname is read-only and contains the name of the interfacewhich 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>

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:

https://github.com/felipebalbi/usb-tools.git master

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 thisfunction instance

Testing the PHONET function¶

It is not possible to test the SOCK_STREAM protocol without a specific pieceof 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

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 thisfunction instance
qmult	queue length multiplier for high and super speed
host_addr	MAC address of host’s end of thisEthernet over USB link
dev_addr	MAC address of device’s end of thisEthernet over USB link

and after creating the functions/rndis.<instance name> they contain defaultvalues: 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 aconfiguration. The ifname is read-only and contains the name of the interfacewhich 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>

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 usbserialecho 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>

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)

Function-specific configfs interface¶

The function name to use when creating the function directoryis “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

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 captureand playback

The attributes have sane default values.

Testing the UAC2 function¶

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

This function does not require real hardware support, it justsends a stream of audio data to/from the host. In order toactually hear something at the device side, a command similarto 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

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 ofsending or receiving when this configuration isselected

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

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

Each frame description contains frame interval specification, and eachsuch specification consists of a number of lines with an inverval valuein 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/dwFrameInterval66666610000005000000EOF# 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:

http://www.spinics.net/lists/linux-usb/msg99220.html

host:

luvcview -f yuv

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_exampledescribed in Documentation/usb/gadget_printer.rst.

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 captureand playback

The attributes have sane default values.

Testing the UAC1 function¶

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

This function does not require real hardware support, it justsends a stream of audio data to/from the host. In order toactually hear something at the device side, a command similarto 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