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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
240host: test-usb
241
242http://www.linux-usb.org/usbtest/testusb.c
Andrzej Pietrasiewiczcdbe2872014-12-16 14:56:32 +0100243
2448. MASS STORAGE function
245========================
246
247The function is provided by usb_f_mass_storage.ko module.
248
249Function-specific configfs interface
250------------------------------------
251
252The function name to use when creating the function directory is "mass_storage".
253The MASS STORAGE function provides these attributes in its directory:
254files:
255
256 stall - Set to permit function to halt bulk endpoints.
257 Disabled on some USB devices known not to work
258 correctly. You should set it to true.
259 num_buffers - Number of pipeline buffers. Valid numbers
260 are 2..4. Available only if
261 CONFIG_USB_GADGET_DEBUG_FILES is set.
262
263and a default lun.0 directory corresponding to SCSI LUN #0.
264
265A new lun can be added with mkdir:
266
267$ mkdir functions/mass_storage.0/partition.5
268
269Lun numbering does not have to be continuous, except for lun #0 which is
270created by default. A maximum of 8 luns can be specified and they all must be
271named following the <name>.<number> scheme. The numbers can be 0..8.
272Probably a good convention is to name the luns "lun.<number>",
273although it is not mandatory.
274
275In each lun directory there are the following attribute files:
276
277 file - The path to the backing file for the LUN.
278 Required if LUN is not marked as removable.
279 ro - Flag specifying access to the LUN shall be
280 read-only. This is implied if CD-ROM emulation
281 is enabled as well as when it was impossible
282 to open "filename" in R/W mode.
283 removable - Flag specifying that LUN shall be indicated as
284 being removable.
285 cdrom - Flag specifying that LUN shall be reported as
286 being a CD-ROM.
287 nofua - Flag specifying that FUA flag
288 in SCSI WRITE(10,12)
289
290Testing the MASS STORAGE function
291---------------------------------
292
293device: connect the gadget, enable it
294host: dmesg, see the USB drives appear (if system configured to automatically
295mount)
Andrzej Pietrasiewicz0d6be592014-12-16 14:56:33 +0100296
2979. MIDI function
298================
299
300The function is provided by usb_f_midi.ko module.
301
302Function-specific configfs interface
303------------------------------------
304
305The function name to use when creating the function directory is "midi".
306The MIDI function provides these attributes in its function directory:
307
308 buflen - MIDI buffer length
309 id - ID string for the USB MIDI adapter
310 in_ports - number of MIDI input ports
311 index - index value for the USB MIDI adapter
312 out_ports - number of MIDI output ports
313 qlen - USB read request queue length
314
315Testing the MIDI function
316-------------------------
317
318There are two cases: playing a mid from the gadget to
319the host and playing a mid from the host to the gadget.
320
3211) Playing a mid from the gadget to the host
322host)
323
324$ arecordmidi -l
325 Port Client name Port name
326 14:0 Midi Through Midi Through Port-0
327 24:0 MIDI Gadget MIDI Gadget MIDI 1
328$ arecordmidi -p 24:0 from_gadget.mid
329
330gadget)
331
332$ aplaymidi -l
333 Port Client name Port name
334 20:0 f_midi f_midi
335
336$ aplaymidi -p 20:0 to_host.mid
337
3382) Playing a mid from the host to the gadget
339gadget)
340
341$ arecordmidi -l
342 Port Client name Port name
343 20:0 f_midi f_midi
344
345$ arecordmidi -p 20:0 from_host.mid
346
347host)
348
349$ aplaymidi -l
350 Port Client name Port name
351 14:0 Midi Through Midi Through Port-0
352 24:0 MIDI Gadget MIDI Gadget MIDI 1
353
354$ aplaymidi -p24:0 to_gadget.mid
355
356The from_gadget.mid should sound identical to the to_host.mid.
357The from_host.id should sound identical to the to_gadget.mid.
358
359MIDI files can be played to speakers/headphones with e.g. timidity installed
360
361$ aplaymidi -l
362 Port Client name Port name
363 14:0 Midi Through Midi Through Port-0
364 24:0 MIDI Gadget MIDI Gadget MIDI 1
365128:0 TiMidity TiMidity port 0
366128:1 TiMidity TiMidity port 1
367128:2 TiMidity TiMidity port 2
368128:3 TiMidity TiMidity port 3
369
370$ aplaymidi -p 128:0 file.mid
371
372MIDI ports can be logically connected using the aconnect utility, e.g.:
373
374$ aconnect 24:0 128:0 # try it on the host
375
376After the gadget's MIDI port is connected to timidity's MIDI port,
377whatever is played at the gadget side with aplaymidi -l is audible
378in host's speakers/headphones.
Andrzej Pietrasiewicz4d0fa792014-12-16 14:56:34 +0100379
38010. NCM function
381================
382
383The function is provided by usb_f_ncm.ko module.
384
385Function-specific configfs interface
386------------------------------------
387
388The function name to use when creating the function directory is "ncm".
389The NCM function provides these attributes in its function directory:
390
391 ifname - network device interface name associated with this
392 function instance
393 qmult - queue length multiplier for high and super speed
394 host_addr - MAC address of host's end of this
395 Ethernet over USB link
396 dev_addr - MAC address of device's end of this
397 Ethernet over USB link
398
399and after creating the functions/ncm.<instance name> they contain default
400values: qmult is 5, dev_addr and host_addr are randomly selected.
401Except for ifname they can be written to until the function is linked to a
402configuration. The ifname is read-only and contains the name of the interface
403which was assigned by the net core, e. g. usb0.
404
405Testing the NCM function
406------------------------
407
408Configure IP addresses of the device and the host. Then:
409
410On the device: ping <host's IP>
411On the host: ping <device's IP>
Andrzej Pietrasiewiczd81b85d2014-12-16 14:56:35 +0100412
41311. OBEX function
414=================
415
416The function is provided by usb_f_obex.ko module.
417
418Function-specific configfs interface
419------------------------------------
420
421The function name to use when creating the function directory is "obex".
422The OBEX function provides just one attribute in its function directory:
423
424 port_num
425
426The attribute is read-only.
427
428There can be at most 4 ACM/generic serial/OBEX ports in the system.
429
430Testing the OBEX function
431-------------------------
432
433On device: seriald -f /dev/ttyGS<Y> -s 1024
434On host: serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
435 -t<out endpoint addr> -r<in endpoint addr>
436
437where seriald and serialc are Felipe's utilities found here:
438
439https://git.gitorious.org/usb/usb-tools.git master
Andrzej Pietrasiewiczda2907d2014-12-16 14:56:36 +0100440
44112. PHONET function
442===================
443
444The function is provided by usb_f_phonet.ko module.
445
446Function-specific configfs interface
447------------------------------------
448
449The function name to use when creating the function directory is "phonet".
450The PHONET function provides just one attribute in its function directory:
451
452 ifname - network device interface name associated with this
453 function instance
454
455Testing the PHONET function
456---------------------------
457
458It is not possible to test the SOCK_STREAM protocol without a specific piece
459of hardware, so only SOCK_DGRAM has been tested. For the latter to work,
460in the past I had to apply the patch mentioned here:
461
462http://www.spinics.net/lists/linux-usb/msg85689.html
463
464These tools are required:
465
466git://git.gitorious.org/meego-cellular/phonet-utils.git
467
468On the host:
469
470$ ./phonet -a 0x10 -i usbpn0
471$ ./pnroute add 0x6c usbpn0
472$./pnroute add 0x10 usbpn0
473$ ifconfig usbpn0 up
474
475On the device:
476
477$ ./phonet -a 0x6c -i upnlink0
478$ ./pnroute add 0x10 upnlink0
479$ ifconfig upnlink0 up
480
481Then a test program can be used:
482
483http://www.spinics.net/lists/linux-usb/msg85690.html
484
485On the device:
486
487$ ./pnxmit -a 0x6c -r
488
489On the host:
490
491$ ./pnxmit -a 0x10 -s 0x6c
492
493As a result some data should be sent from host to device.
494Then the other way round:
495
496On the host:
497
498$ ./pnxmit -a 0x10 -r
499
500On the device:
501
502$ ./pnxmit -a 0x6c -s 0x10
Andrzej Pietrasiewiczddb72242014-12-16 14:56:37 +0100503
50413. RNDIS function
505==================
506
507The function is provided by usb_f_rndis.ko module.
508
509Function-specific configfs interface
510------------------------------------
511
512The function name to use when creating the function directory is "rndis".
513The RNDIS function provides these attributes in its function directory:
514
515 ifname - network device interface name associated with this
516 function instance
517 qmult - queue length multiplier for high and super speed
518 host_addr - MAC address of host's end of this
519 Ethernet over USB link
520 dev_addr - MAC address of device's end of this
521 Ethernet over USB link
522
523and after creating the functions/rndis.<instance name> they contain default
524values: qmult is 5, dev_addr and host_addr are randomly selected.
525Except for ifname they can be written to until the function is linked to a
526configuration. The ifname is read-only and contains the name of the interface
527which was assigned by the net core, e. g. usb0.
528
529By default there can be only 1 RNDIS interface in the system.
530
531Testing the RNDIS function
532--------------------------
533
534Configure IP addresses of the device and the host. Then:
535
536On the device: ping <host's IP>
537On the host: ping <device's IP>
Andrzej Pietrasiewicz4dfcec82014-12-16 14:56:38 +0100538
53914. SERIAL function
540===================
541
542The function is provided by usb_f_gser.ko module.
543
544Function-specific configfs interface
545------------------------------------
546
547The function name to use when creating the function directory is "gser".
548The SERIAL function provides just one attribute in its function directory:
549
550 port_num
551
552The attribute is read-only.
553
554There can be at most 4 ACM/generic serial/OBEX ports in the system.
555
556Testing the SERIAL function
557---------------------------
558
559On host: insmod usbserial
560 echo VID PID >/sys/bus/usb-serial/drivers/generic/new_id
561On host: cat > /dev/ttyUSB<X>
562On target: cat /dev/ttyGS<Y>
563
564then the other way round
565
566On target: cat > /dev/ttyGS<Y>
567On host: cat /dev/ttyUSB<X>
Andrzej Pietrasiewicz480a9122014-12-16 14:56:39 +0100568
56915. SOURCESINK function
570=======================
571
572The function is provided by usb_f_ss_lb.ko module.
573
574Function-specific configfs interface
575------------------------------------
576
577The function name to use when creating the function directory is "SourceSink".
578The SOURCESINK function provides these attributes in its function directory:
579
580 pattern - 0 (all zeros), 1 (mod63), 2 (none)
581 isoc_interval - 1..16
582 isoc_maxpacket - 0 - 1023 (fs), 0 - 1024 (hs/ss)
583 isoc_mult - 0..2 (hs/ss only)
584 isoc_maxburst - 0..15 (ss only)
585 bulk_buflen - buffer length
586
587Testing the SOURCESINK function
588-------------------------------
589
590device: run the gadget
591host: test-usb
592
593http://www.linux-usb.org/usbtest/testusb.c
Andrzej Pietrasiewiczdae03582014-12-16 14:56:40 +0100594
59516. UAC1 function
596=================
597
598The function is provided by usb_f_uac1.ko module.
599
600Function-specific configfs interface
601------------------------------------
602
603The function name to use when creating the function directory is "uac1".
604The uac1 function provides these attributes in its function directory:
605
606 audio_buf_size - audio buffer size
607 fn_cap - capture pcm device file name
608 fn_cntl - control device file name
609 fn_play - playback pcm device file name
610 req_buf_size - ISO OUT endpoint request buffer size
611 req_count - ISO OUT endpoint request count
612
613The attributes have sane default values.
614
615Testing the UAC1 function
616-------------------------
617
618device: run the gadget
619host: aplay -l # should list our USB Audio Gadget
Andrzej Pietrasiewicz020c6f92014-12-16 14:56:41 +0100620
62117. UAC2 function
622=================
623
624The function is provided by usb_f_uac2.ko module.
625
626Function-specific configfs interface
627------------------------------------
628
629The function name to use when creating the function directory is "uac2".
630The uac2 function provides these attributes in its function directory:
631
632 chmask - capture channel mask
633 c_srate - capture sampling rate
634 c_ssize - capture sample size (bytes)
635 p_chmask - playback channel mask
636 p_srate - playback sampling rate
637 p_ssize - playback sample size (bytes)
638
639The attributes have sane default values.
640
641Testing the UAC2 function
642-------------------------
643
644device: run the gadget
645host: aplay -l # should list our USB Audio Gadget
646
647This function does not require real hardware support, it just
648sends a stream of audio data to/from the host. In order to
649actually hear something at the device side, a command similar
650to this must be used at the device side:
651
652$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &
653
654e.g.:
655
656$ arecord -f dat -t wav -D hw:CARD=UAC2Gadget,DEV=0 | \
657aplay -D default:CARD=OdroidU3
Andrzej Pietrasiewicz9c4f5382014-12-16 14:56:42 +0100658
65918. UVC function
660================
661
662The function is provided by usb_f_uvc.ko module.
663
664Function-specific configfs interface
665------------------------------------
666
667The function name to use when creating the function directory is "uvc".
668The uvc function provides these attributes in its function directory:
669
670 streaming_interval - interval for polling endpoint for data transfers
671 streaming_maxburst - bMaxBurst for super speed companion descriptor
672 streaming_maxpacket - maximum packet size this endpoint is capable of
673 sending or receiving when this configuration is
674 selected
675
676There are also "control" and "streaming" subdirectories, each of which contain
677a number of their subdirectories. There are some sane defaults provided, but
678the user must provide the following:
679
680 control header - create in control/header, link from control/class/fs
681 and/or control/class/ss
682 streaming header - create in streaming/header, link from
683 streaming/class/fs and/or streaming/class/hs and/or
684 streaming/class/ss
685 format description - create in streaming/mjpeg and/or
686 streaming/uncompressed
687 frame description - create in streaming/mjpeg/<format> and/or in
688 streaming/uncompressed/<format>
689
690Each frame description contains frame interval specification, and each
691such specification consists of a number of lines with an inverval value
692in each line. The rules stated above are best illustrated with an example:
693
694# mkdir functions/uvc.usb0/control/header/h
695# cd functions/uvc.usb0/control/header/h
696# ln -s header/h class/fs
697# ln -s header/h class/ss
698# mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
699# cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/360p/dwFrameInterval
700666666
7011000000
7025000000
703EOF
704# cd $GADGET_CONFIGFS_ROOT
705# mkdir functions/uvc.usb0/streaming/header/h
706# cd functions/uvc.usb0/streaming/header/h
707# ln -s ../../uncompressed/u
708# cd ../../class/fs
709# ln -s ../../header/h
710# cd ../../class/hs
711# ln -s ../../header/h
712# cd ../../class/ss
713# ln -s ../../header/h
714
715
716Testing the UVC function
717------------------------
718
719device: run the gadget, modprobe vivid
720
721# uvc-gadget -u /dev/video<uvc video node #> -v /dev/video<vivid video node #>
722
723where uvc-gadget is this program:
724http://git.ideasonboard.org/uvc-gadget.git
725
726with these patches:
727http://www.spinics.net/lists/linux-usb/msg99220.html
728
729host: luvcview -f yuv
Andrzej Pietrasiewiczee1cd512015-03-03 10:52:32 +0100730
73119. PRINTER function
732====================
733
734The function is provided by usb_f_printer.ko module.
735
736Function-specific configfs interface
737------------------------------------
738
739The function name to use when creating the function directory is "printer".
740The printer function provides these attributes in its function directory:
741
742 pnp_string - Data to be passed to the host in pnp string
743 q_len - Number of requests per endpoint
744
745Testing the PRINTER function
746----------------------------
747
748The most basic testing:
749
750device: run the gadget
751# ls -l /devices/virtual/usb_printer_gadget/
752
753should show g_printer<number>.
754
755If udev is active, then /dev/g_printer<number> should appear automatically.
756
757host:
758
759If udev is active, then e.g. /dev/usb/lp0 should appear.
760
761host->device transmission:
762
763device:
764# cat /dev/g_printer<number>
765host:
766# cat > /dev/usb/lp0
767
768device->host transmission:
769
770# cat > /dev/g_printer<number>
771host:
772# cat /dev/usb/lp0
773
774More advanced testing can be done with the prn_example
775described in Documentation/usb/gadget-printer.txt.