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
  10. NCM function
  11. OBEX function
  12. PHONET function
  13. RNDIS function
  14. SERIAL function
  15. SOURCESINK function
  16. UAC1 function
  17. UAC2 function
  18. UVC function
  19. PRINTER 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 (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
  
  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.
  
  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:
  
  https://git.gitorious.org/usb/usb-tools.git master
  
  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
  
  Testing the SOURCESINK function
  -------------------------------
  
  device: run the gadget
  host: test-usb (tools/usb/testusb.c)
  
  
  16. UAC1 function
  =================
  
  The function is provided by usb_f_uac1.ko module.
  
  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:
  
  	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)
  
  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/header/h
  # 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:
  http://www.spinics.net/lists/linux-usb/msg99220.html
  
  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.txt.