blob: b24d3ef89166bc16f228e97aceb6f300063edc2a [file] [log] [blame]
Andrzej Pietrasiewicze38eb2c2014-12-16 14:56:25 +01001This file summarizes information on basic testing of USB functions
2provided by gadgets.
3
41. ACM function
Andrzej Pietrasiewiczd5862ca2014-12-16 14:56:26 +010052. ECM function
Andrzej Pietrasiewicz7bfbc6e2014-12-16 14:56:27 +010063. ECM subset function
Andrzej Pietrasiewicz4ca560a2014-12-16 14:56:28 +010074. EEM function
Andrzej Pietrasiewicz2c0f62f2014-12-16 14:56:29 +010085. FFS function
Andrzej Pietrasiewiczf7e3c3c2014-12-16 14:56:30 +010096. HID function
Andrzej Pietrasiewiczec91aff2014-12-16 14:56:31 +0100107. LOOPBACK function
Andrzej Pietrasiewiczcdbe2872014-12-16 14:56:32 +0100118. MASS STORAGE function
Andrzej Pietrasiewicz0d6be592014-12-16 14:56:33 +0100129. MIDI function
Andrzej Pietrasiewicz4d0fa792014-12-16 14:56:34 +01001310. NCM function
Andrzej Pietrasiewiczd81b85d2014-12-16 14:56:35 +01001411. OBEX function
Andrzej Pietrasiewiczda2907d2014-12-16 14:56:36 +01001512. PHONET function
Andrzej Pietrasiewiczddb72242014-12-16 14:56:37 +01001613. RNDIS function
Andrzej Pietrasiewicz4dfcec82014-12-16 14:56:38 +01001714. SERIAL function
Andrzej Pietrasiewicz480a9122014-12-16 14:56:39 +01001815. SOURCESINK function
Andrzej Pietrasiewiczdae03582014-12-16 14:56:40 +01001916. UAC1 function
Andrzej Pietrasiewicz020c6f92014-12-16 14:56:41 +01002017. UAC2 function
Andrzej Pietrasiewicz9c4f5382014-12-16 14:56:42 +01002118. UVC function
Andrzej Pietrasiewiczee1cd512015-03-03 10:52:32 +01002219. PRINTER function
Andrzej Pietrasiewicze38eb2c2014-12-16 14:56:25 +010023
24
251. ACM function
26===============
27
28The function is provided by usb_f_acm.ko module.
29
30Function-specific configfs interface
31------------------------------------
32
33The function name to use when creating the function directory is "acm".
34The ACM function provides just one attribute in its function directory:
35
36 port_num
37
38The attribute is read-only.
39
40There can be at most 4 ACM/generic serial/OBEX ports in the system.
41
42
43Testing the ACM function
44------------------------
45
46On the host: cat > /dev/ttyACM<X>
47On the device : cat /dev/ttyGS<Y>
48
49then the other way round
50
51On the device: cat > /dev/ttyGS<Y>
52On the host: cat /dev/ttyACM<X>
Andrzej Pietrasiewiczd5862ca2014-12-16 14:56:26 +010053
542. ECM function
55===============
56
57The function is provided by usb_f_ecm.ko module.
58
59Function-specific configfs interface
60------------------------------------
61
62The function name to use when creating the function directory is "ecm".
63The ECM function provides these attributes in its function directory:
64
65 ifname - network device interface name associated with this
66 function instance
67 qmult - queue length multiplier for high and super speed
68 host_addr - MAC address of host's end of this
69 Ethernet over USB link
70 dev_addr - MAC address of device's end of this
71 Ethernet over USB link
72
73and after creating the functions/ecm.<instance name> they contain default
74values: qmult is 5, dev_addr and host_addr are randomly selected.
75Except for ifname they can be written to until the function is linked to a
76configuration. The ifname is read-only and contains the name of the interface
77which was assigned by the net core, e. g. usb0.
78
79Testing the ECM function
80------------------------
81
82Configure IP addresses of the device and the host. Then:
83
84On the device: ping <host's IP>
85On the host: ping <device's IP>
Andrzej Pietrasiewicz7bfbc6e2014-12-16 14:56:27 +010086
873. ECM subset function
88======================
89
90The function is provided by usb_f_ecm_subset.ko module.
91
92Function-specific configfs interface
93------------------------------------
94
95The function name to use when creating the function directory is "geth".
96The ECM subset function provides these attributes in its function directory:
97
98 ifname - network device interface name associated with this
99 function instance
100 qmult - queue length multiplier for high and super speed
101 host_addr - MAC address of host's end of this
102 Ethernet over USB link
103 dev_addr - MAC address of device's end of this
104 Ethernet over USB link
105
106and after creating the functions/ecm.<instance name> they contain default
107values: qmult is 5, dev_addr and host_addr are randomly selected.
108Except for ifname they can be written to until the function is linked to a
109configuration. The ifname is read-only and contains the name of the interface
110which was assigned by the net core, e. g. usb0.
111
112Testing the ECM subset function
113-------------------------------
114
115Configure IP addresses of the device and the host. Then:
116
117On the device: ping <host's IP>
118On the host: ping <device's IP>
Andrzej Pietrasiewicz4ca560a2014-12-16 14:56:28 +0100119
1204. EEM function
121===============
122
123The function is provided by usb_f_eem.ko module.
124
125Function-specific configfs interface
126------------------------------------
127
128The function name to use when creating the function directory is "eem".
129The EEM function provides these attributes in its function directory:
130
131 ifname - network device interface name associated with this
132 function instance
133 qmult - queue length multiplier for high and super speed
134 host_addr - MAC address of host's end of this
135 Ethernet over USB link
136 dev_addr - MAC address of device's end of this
137 Ethernet over USB link
138
139and after creating the functions/eem.<instance name> they contain default
140values: qmult is 5, dev_addr and host_addr are randomly selected.
141Except for ifname they can be written to until the function is linked to a
142configuration. The ifname is read-only and contains the name of the interface
143which was assigned by the net core, e. g. usb0.
144
145Testing the EEM function
146------------------------
147
148Configure IP addresses of the device and the host. Then:
149
150On the device: ping <host's IP>
151On the host: ping <device's IP>
Andrzej Pietrasiewicz2c0f62f2014-12-16 14:56:29 +0100152
1535. FFS function
154===============
155
156The function is provided by usb_f_fs.ko module.
157
158Function-specific configfs interface
159------------------------------------
160
161The function name to use when creating the function directory is "ffs".
162The function directory is intentionally empty and not modifiable.
163
164After creating the directory there is a new instance (a "device") of FunctionFS
165available in the system. Once a "device" is available, the user should follow
166the standard procedure for using FunctionFS (mount it, run the userspace
167process which implements the function proper). The gadget should be enabled
168by writing a suitable string to usb_gadget/<gadget>/UDC.
169
170Testing the FFS function
171------------------------
172
173On the device: start the function's userspace daemon, enable the gadget
174On the host: use the USB function provided by the device
Andrzej Pietrasiewiczf7e3c3c2014-12-16 14:56:30 +0100175
1766. HID function
177===============
178
179The function is provided by usb_f_hid.ko module.
180
181Function-specific configfs interface
182------------------------------------
183
184The function name to use when creating the function directory is "hid".
185The HID function provides these attributes in its function directory:
186
187 protocol - HID protocol to use
188 report_desc - data to be used in HID reports, except data
189 passed with /dev/hidg<X>
190 report_length - HID report length
191 subclass - HID subclass to use
192
193For a keyboard the protocol and the subclass are 1, the report_length is 8,
194while the report_desc is:
195
196$ hd my_report_desc
19700000000 05 01 09 06 a1 01 05 07 19 e0 29 e7 15 00 25 01 |..........)...%.|
19800000010 75 01 95 08 81 02 95 01 75 08 81 03 95 05 75 01 |u.......u.....u.|
19900000020 05 08 19 01 29 05 91 02 95 01 75 03 91 03 95 06 |....).....u.....|
20000000030 75 08 15 00 25 65 05 07 19 00 29 65 81 00 c0 |u...%e....)e...|
2010000003f
202
203Such a sequence of bytes can be stored to the attribute with echo:
204
205$ echo -ne \\x05\\x01\\x09\\x06\\xa1.....
206
207Testing the HID function
208------------------------
209
210Device:
211- create the gadget
212- connect the gadget to a host, preferably not the one used
213to control the gadget
214- run a program which writes to /dev/hidg<N>, e.g.
215a userspace program found in Documentation/usb/gadget_hid.txt:
216
217$ ./hid_gadget_test /dev/hidg0 keyboard
218
219Host:
220- observe the keystrokes from the gadget
Andrzej Pietrasiewiczec91aff2014-12-16 14:56:31 +0100221
2227. LOOPBACK function
223====================
224
225The function is provided by usb_f_ss_lb.ko module.
226
227Function-specific configfs interface
228------------------------------------
229
230The function name to use when creating the function directory is "Loopback".
231The LOOPBACK function provides these attributes in its function directory:
232
233 qlen - depth of loopback queue
234 bulk_buflen - buffer length
235
236Testing the LOOPBACK function
237-----------------------------
238
239device: run the gadget
Peter Chenf811a382015-07-31 16:36:30 +0800240host: test-usb (tools/usb/testusb.c)
Andrzej Pietrasiewiczcdbe2872014-12-16 14:56:32 +0100241
2428. MASS STORAGE function
243========================
244
245The function is provided by usb_f_mass_storage.ko module.
246
247Function-specific configfs interface
248------------------------------------
249
250The function name to use when creating the function directory is "mass_storage".
251The MASS STORAGE function provides these attributes in its directory:
252files:
253
254 stall - Set to permit function to halt bulk endpoints.
255 Disabled on some USB devices known not to work
256 correctly. You should set it to true.
257 num_buffers - Number of pipeline buffers. Valid numbers
258 are 2..4. Available only if
259 CONFIG_USB_GADGET_DEBUG_FILES is set.
260
261and a default lun.0 directory corresponding to SCSI LUN #0.
262
263A new lun can be added with mkdir:
264
265$ mkdir functions/mass_storage.0/partition.5
266
267Lun numbering does not have to be continuous, except for lun #0 which is
268created by default. A maximum of 8 luns can be specified and they all must be
269named following the <name>.<number> scheme. The numbers can be 0..8.
270Probably a good convention is to name the luns "lun.<number>",
271although it is not mandatory.
272
273In each lun directory there are the following attribute files:
274
275 file - The path to the backing file for the LUN.
276 Required if LUN is not marked as removable.
277 ro - Flag specifying access to the LUN shall be
278 read-only. This is implied if CD-ROM emulation
279 is enabled as well as when it was impossible
280 to open "filename" in R/W mode.
281 removable - Flag specifying that LUN shall be indicated as
282 being removable.
283 cdrom - Flag specifying that LUN shall be reported as
284 being a CD-ROM.
285 nofua - Flag specifying that FUA flag
286 in SCSI WRITE(10,12)
287
288Testing the MASS STORAGE function
289---------------------------------
290
291device: connect the gadget, enable it
292host: dmesg, see the USB drives appear (if system configured to automatically
293mount)
Andrzej Pietrasiewicz0d6be592014-12-16 14:56:33 +0100294
2959. MIDI function
296================
297
298The function is provided by usb_f_midi.ko module.
299
300Function-specific configfs interface
301------------------------------------
302
303The function name to use when creating the function directory is "midi".
304The MIDI function provides these attributes in its function directory:
305
306 buflen - MIDI buffer length
307 id - ID string for the USB MIDI adapter
308 in_ports - number of MIDI input ports
309 index - index value for the USB MIDI adapter
310 out_ports - number of MIDI output ports
311 qlen - USB read request queue length
312
313Testing the MIDI function
314-------------------------
315
316There are two cases: playing a mid from the gadget to
317the host and playing a mid from the host to the gadget.
318
3191) Playing a mid from the gadget to the host
320host)
321
322$ arecordmidi -l
323 Port Client name Port name
324 14:0 Midi Through Midi Through Port-0
325 24:0 MIDI Gadget MIDI Gadget MIDI 1
326$ arecordmidi -p 24:0 from_gadget.mid
327
328gadget)
329
330$ aplaymidi -l
331 Port Client name Port name
332 20:0 f_midi f_midi
333
334$ aplaymidi -p 20:0 to_host.mid
335
3362) Playing a mid from the host to the gadget
337gadget)
338
339$ arecordmidi -l
340 Port Client name Port name
341 20:0 f_midi f_midi
342
343$ arecordmidi -p 20:0 from_host.mid
344
345host)
346
347$ aplaymidi -l
348 Port Client name Port name
349 14:0 Midi Through Midi Through Port-0
350 24:0 MIDI Gadget MIDI Gadget MIDI 1
351
352$ aplaymidi -p24:0 to_gadget.mid
353
354The from_gadget.mid should sound identical to the to_host.mid.
355The from_host.id should sound identical to the to_gadget.mid.
356
357MIDI files can be played to speakers/headphones with e.g. timidity installed
358
359$ aplaymidi -l
360 Port Client name Port name
361 14:0 Midi Through Midi Through Port-0
362 24:0 MIDI Gadget MIDI Gadget MIDI 1
363128:0 TiMidity TiMidity port 0
364128:1 TiMidity TiMidity port 1
365128:2 TiMidity TiMidity port 2
366128:3 TiMidity TiMidity port 3
367
368$ aplaymidi -p 128:0 file.mid
369
370MIDI ports can be logically connected using the aconnect utility, e.g.:
371
372$ aconnect 24:0 128:0 # try it on the host
373
374After the gadget's MIDI port is connected to timidity's MIDI port,
375whatever is played at the gadget side with aplaymidi -l is audible
376in host's speakers/headphones.
Andrzej Pietrasiewicz4d0fa792014-12-16 14:56:34 +0100377
37810. NCM function
379================
380
381The function is provided by usb_f_ncm.ko module.
382
383Function-specific configfs interface
384------------------------------------
385
386The function name to use when creating the function directory is "ncm".
387The NCM function provides these attributes in its function directory:
388
389 ifname - network device interface name associated with this
390 function instance
391 qmult - queue length multiplier for high and super speed
392 host_addr - MAC address of host's end of this
393 Ethernet over USB link
394 dev_addr - MAC address of device's end of this
395 Ethernet over USB link
396
397and after creating the functions/ncm.<instance name> they contain default
398values: qmult is 5, dev_addr and host_addr are randomly selected.
399Except for ifname they can be written to until the function is linked to a
400configuration. The ifname is read-only and contains the name of the interface
401which was assigned by the net core, e. g. usb0.
402
403Testing the NCM function
404------------------------
405
406Configure IP addresses of the device and the host. Then:
407
408On the device: ping <host's IP>
409On the host: ping <device's IP>
Andrzej Pietrasiewiczd81b85d2014-12-16 14:56:35 +0100410
41111. OBEX function
412=================
413
414The function is provided by usb_f_obex.ko module.
415
416Function-specific configfs interface
417------------------------------------
418
419The function name to use when creating the function directory is "obex".
420The OBEX function provides just one attribute in its function directory:
421
422 port_num
423
424The attribute is read-only.
425
426There can be at most 4 ACM/generic serial/OBEX ports in the system.
427
428Testing the OBEX function
429-------------------------
430
431On device: seriald -f /dev/ttyGS<Y> -s 1024
432On host: serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
433 -t<out endpoint addr> -r<in endpoint addr>
434
435where seriald and serialc are Felipe's utilities found here:
436
437https://git.gitorious.org/usb/usb-tools.git master
Andrzej Pietrasiewiczda2907d2014-12-16 14:56:36 +0100438
43912. PHONET function
440===================
441
442The function is provided by usb_f_phonet.ko module.
443
444Function-specific configfs interface
445------------------------------------
446
447The function name to use when creating the function directory is "phonet".
448The PHONET function provides just one attribute in its function directory:
449
450 ifname - network device interface name associated with this
451 function instance
452
453Testing the PHONET function
454---------------------------
455
456It is not possible to test the SOCK_STREAM protocol without a specific piece
457of hardware, so only SOCK_DGRAM has been tested. For the latter to work,
458in the past I had to apply the patch mentioned here:
459
460http://www.spinics.net/lists/linux-usb/msg85689.html
461
462These tools are required:
463
464git://git.gitorious.org/meego-cellular/phonet-utils.git
465
466On the host:
467
468$ ./phonet -a 0x10 -i usbpn0
469$ ./pnroute add 0x6c usbpn0
470$./pnroute add 0x10 usbpn0
471$ ifconfig usbpn0 up
472
473On the device:
474
475$ ./phonet -a 0x6c -i upnlink0
476$ ./pnroute add 0x10 upnlink0
477$ ifconfig upnlink0 up
478
479Then a test program can be used:
480
481http://www.spinics.net/lists/linux-usb/msg85690.html
482
483On the device:
484
485$ ./pnxmit -a 0x6c -r
486
487On the host:
488
489$ ./pnxmit -a 0x10 -s 0x6c
490
491As a result some data should be sent from host to device.
492Then the other way round:
493
494On the host:
495
496$ ./pnxmit -a 0x10 -r
497
498On the device:
499
500$ ./pnxmit -a 0x6c -s 0x10
Andrzej Pietrasiewiczddb72242014-12-16 14:56:37 +0100501
50213. RNDIS function
503==================
504
505The function is provided by usb_f_rndis.ko module.
506
507Function-specific configfs interface
508------------------------------------
509
510The function name to use when creating the function directory is "rndis".
511The RNDIS function provides these attributes in its function directory:
512
513 ifname - network device interface name associated with this
514 function instance
515 qmult - queue length multiplier for high and super speed
516 host_addr - MAC address of host's end of this
517 Ethernet over USB link
518 dev_addr - MAC address of device's end of this
519 Ethernet over USB link
520
521and after creating the functions/rndis.<instance name> they contain default
522values: qmult is 5, dev_addr and host_addr are randomly selected.
523Except for ifname they can be written to until the function is linked to a
524configuration. The ifname is read-only and contains the name of the interface
525which was assigned by the net core, e. g. usb0.
526
Andrzej Pietrasiewiczddb72242014-12-16 14:56:37 +0100527Testing the RNDIS function
528--------------------------
529
530Configure IP addresses of the device and the host. Then:
531
532On the device: ping <host's IP>
533On the host: ping <device's IP>
Andrzej Pietrasiewicz4dfcec82014-12-16 14:56:38 +0100534
53514. SERIAL function
536===================
537
538The function is provided by usb_f_gser.ko module.
539
540Function-specific configfs interface
541------------------------------------
542
543The function name to use when creating the function directory is "gser".
544The SERIAL function provides just one attribute in its function directory:
545
546 port_num
547
548The attribute is read-only.
549
550There can be at most 4 ACM/generic serial/OBEX ports in the system.
551
552Testing the SERIAL function
553---------------------------
554
555On host: insmod usbserial
556 echo VID PID >/sys/bus/usb-serial/drivers/generic/new_id
557On host: cat > /dev/ttyUSB<X>
558On target: cat /dev/ttyGS<Y>
559
560then the other way round
561
562On target: cat > /dev/ttyGS<Y>
563On host: cat /dev/ttyUSB<X>
Andrzej Pietrasiewicz480a9122014-12-16 14:56:39 +0100564
56515. SOURCESINK function
566=======================
567
568The function is provided by usb_f_ss_lb.ko module.
569
570Function-specific configfs interface
571------------------------------------
572
573The function name to use when creating the function directory is "SourceSink".
574The SOURCESINK function provides these attributes in its function directory:
575
576 pattern - 0 (all zeros), 1 (mod63), 2 (none)
577 isoc_interval - 1..16
578 isoc_maxpacket - 0 - 1023 (fs), 0 - 1024 (hs/ss)
579 isoc_mult - 0..2 (hs/ss only)
580 isoc_maxburst - 0..15 (ss only)
581 bulk_buflen - buffer length
582
583Testing the SOURCESINK function
584-------------------------------
585
586device: run the gadget
Peter Chenf811a382015-07-31 16:36:30 +0800587host: test-usb (tools/usb/testusb.c)
Andrzej Pietrasiewicz480a9122014-12-16 14:56:39 +0100588
Andrzej Pietrasiewiczdae03582014-12-16 14:56:40 +0100589
59016. UAC1 function
591=================
592
593The function is provided by usb_f_uac1.ko module.
594
595Function-specific configfs interface
596------------------------------------
597
598The function name to use when creating the function directory is "uac1".
599The uac1 function provides these attributes in its function directory:
600
601 audio_buf_size - audio buffer size
602 fn_cap - capture pcm device file name
603 fn_cntl - control device file name
604 fn_play - playback pcm device file name
605 req_buf_size - ISO OUT endpoint request buffer size
606 req_count - ISO OUT endpoint request count
607
608The attributes have sane default values.
609
610Testing the UAC1 function
611-------------------------
612
613device: run the gadget
614host: aplay -l # should list our USB Audio Gadget
Andrzej Pietrasiewicz020c6f92014-12-16 14:56:41 +0100615
61617. UAC2 function
617=================
618
619The function is provided by usb_f_uac2.ko module.
620
621Function-specific configfs interface
622------------------------------------
623
624The function name to use when creating the function directory is "uac2".
625The uac2 function provides these attributes in its function directory:
626
Peter Chen4e39aca2015-03-27 16:32:18 +0800627 c_chmask - capture channel mask
Andrzej Pietrasiewicz020c6f92014-12-16 14:56:41 +0100628 c_srate - capture sampling rate
629 c_ssize - capture sample size (bytes)
630 p_chmask - playback channel mask
631 p_srate - playback sampling rate
632 p_ssize - playback sample size (bytes)
633
634The attributes have sane default values.
635
636Testing the UAC2 function
637-------------------------
638
639device: run the gadget
640host: aplay -l # should list our USB Audio Gadget
641
642This function does not require real hardware support, it just
643sends a stream of audio data to/from the host. In order to
644actually hear something at the device side, a command similar
645to this must be used at the device side:
646
647$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &
648
649e.g.:
650
651$ arecord -f dat -t wav -D hw:CARD=UAC2Gadget,DEV=0 | \
652aplay -D default:CARD=OdroidU3
Andrzej Pietrasiewicz9c4f5382014-12-16 14:56:42 +0100653
65418. UVC function
655================
656
657The function is provided by usb_f_uvc.ko module.
658
659Function-specific configfs interface
660------------------------------------
661
662The function name to use when creating the function directory is "uvc".
663The uvc function provides these attributes in its function directory:
664
665 streaming_interval - interval for polling endpoint for data transfers
666 streaming_maxburst - bMaxBurst for super speed companion descriptor
667 streaming_maxpacket - maximum packet size this endpoint is capable of
668 sending or receiving when this configuration is
669 selected
670
671There are also "control" and "streaming" subdirectories, each of which contain
672a number of their subdirectories. There are some sane defaults provided, but
673the user must provide the following:
674
675 control header - create in control/header, link from control/class/fs
676 and/or control/class/ss
677 streaming header - create in streaming/header, link from
678 streaming/class/fs and/or streaming/class/hs and/or
679 streaming/class/ss
680 format description - create in streaming/mjpeg and/or
681 streaming/uncompressed
682 frame description - create in streaming/mjpeg/<format> and/or in
683 streaming/uncompressed/<format>
684
685Each frame description contains frame interval specification, and each
686such specification consists of a number of lines with an inverval value
687in each line. The rules stated above are best illustrated with an example:
688
689# mkdir functions/uvc.usb0/control/header/h
690# cd functions/uvc.usb0/control/header/h
691# ln -s header/h class/fs
692# ln -s header/h class/ss
693# mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
694# cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/360p/dwFrameInterval
695666666
6961000000
6975000000
698EOF
699# cd $GADGET_CONFIGFS_ROOT
700# mkdir functions/uvc.usb0/streaming/header/h
701# cd functions/uvc.usb0/streaming/header/h
702# ln -s ../../uncompressed/u
703# cd ../../class/fs
704# ln -s ../../header/h
705# cd ../../class/hs
706# ln -s ../../header/h
707# cd ../../class/ss
708# ln -s ../../header/h
709
710
711Testing the UVC function
712------------------------
713
714device: run the gadget, modprobe vivid
715
716# uvc-gadget -u /dev/video<uvc video node #> -v /dev/video<vivid video node #>
717
718where uvc-gadget is this program:
719http://git.ideasonboard.org/uvc-gadget.git
720
721with these patches:
722http://www.spinics.net/lists/linux-usb/msg99220.html
723
724host: luvcview -f yuv
Andrzej Pietrasiewiczee1cd512015-03-03 10:52:32 +0100725
72619. PRINTER function
727====================
728
729The function is provided by usb_f_printer.ko module.
730
731Function-specific configfs interface
732------------------------------------
733
734The function name to use when creating the function directory is "printer".
735The printer function provides these attributes in its function directory:
736
737 pnp_string - Data to be passed to the host in pnp string
738 q_len - Number of requests per endpoint
739
740Testing the PRINTER function
741----------------------------
742
743The most basic testing:
744
745device: run the gadget
746# ls -l /devices/virtual/usb_printer_gadget/
747
748should show g_printer<number>.
749
750If udev is active, then /dev/g_printer<number> should appear automatically.
751
752host:
753
754If udev is active, then e.g. /dev/usb/lp0 should appear.
755
756host->device transmission:
757
758device:
759# cat /dev/g_printer<number>
760host:
761# cat > /dev/usb/lp0
762
763device->host transmission:
764
765# cat > /dev/g_printer<number>
766host:
767# cat /dev/usb/lp0
768
769More advanced testing can be done with the prn_example
770described in Documentation/usb/gadget-printer.txt.