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Documentation / usb / gadget-testing.txt




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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.

1	This file summarizes information on basic testing of USB functions
2	provided by gadgets.
3	
4	1. ACM function
5	2. ECM function
6	3. ECM subset function
7	4. EEM function
8	5. FFS function
9	6. HID function
10	7. LOOPBACK function
11	8. MASS STORAGE function
12	9. MIDI function
13	10. NCM function
14	11. OBEX function
15	12. PHONET function
16	13. RNDIS function
17	14. SERIAL function
18	15. SOURCESINK function
19	16. UAC1 function (legacy implementation)
20	17. UAC2 function
21	18. UVC function
22	19. PRINTER function
23	20. UAC1 function (new API)
24	
25	
26	1. ACM function
27	===============
28	
29	The function is provided by usb_f_acm.ko module.
30	
31	Function-specific configfs interface
32	------------------------------------
33	
34	The function name to use when creating the function directory is "acm".
35	The ACM function provides just one attribute in its function directory:
36	
37		port_num
38	
39	The attribute is read-only.
40	
41	There can be at most 4 ACM/generic serial/OBEX ports in the system.
42	
43	
44	Testing the ACM function
45	------------------------
46	
47	On the host: cat > /dev/ttyACM<X>
48	On the device : cat /dev/ttyGS<Y>
49	
50	then the other way round
51	
52	On the device: cat > /dev/ttyGS<Y>
53	On the host: cat /dev/ttyACM<X>
54	
55	2. ECM function
56	===============
57	
58	The function is provided by usb_f_ecm.ko module.
59	
60	Function-specific configfs interface
61	------------------------------------
62	
63	The function name to use when creating the function directory is "ecm".
64	The ECM function provides these attributes in its function directory:
65	
66		ifname		- network device interface name associated with this
67				function instance
68		qmult		- queue length multiplier for high and super speed
69		host_addr	- MAC address of host's end of this
70				Ethernet over USB link
71		dev_addr	- MAC address of device's end of this
72				Ethernet over USB link
73	
74	and after creating the functions/ecm.<instance name> they contain default
75	values: qmult is 5, dev_addr and host_addr are randomly selected.
76	Except for ifname they can be written to until the function is linked to a
77	configuration. The ifname is read-only and contains the name of the interface
78	which was assigned by the net core, e. g. usb0.
79	
80	Testing the ECM function
81	------------------------
82	
83	Configure IP addresses of the device and the host. Then:
84	
85	On the device: ping <host's IP>
86	On the host: ping <device's IP>
87	
88	3. ECM subset function
89	======================
90	
91	The function is provided by usb_f_ecm_subset.ko module.
92	
93	Function-specific configfs interface
94	------------------------------------
95	
96	The function name to use when creating the function directory is "geth".
97	The ECM subset function provides these attributes in its function directory:
98	
99		ifname		- network device interface name associated with this
100				function instance
101		qmult		- queue length multiplier for high and super speed
102		host_addr	- MAC address of host's end of this
103				Ethernet over USB link
104		dev_addr	- MAC address of device's end of this
105				Ethernet over USB link
106	
107	and after creating the functions/ecm.<instance name> they contain default
108	values: qmult is 5, dev_addr and host_addr are randomly selected.
109	Except for ifname they can be written to until the function is linked to a
110	configuration. The ifname is read-only and contains the name of the interface
111	which was assigned by the net core, e. g. usb0.
112	
113	Testing the ECM subset function
114	-------------------------------
115	
116	Configure IP addresses of the device and the host. Then:
117	
118	On the device: ping <host's IP>
119	On the host: ping <device's IP>
120	
121	4. EEM function
122	===============
123	
124	The function is provided by usb_f_eem.ko module.
125	
126	Function-specific configfs interface
127	------------------------------------
128	
129	The function name to use when creating the function directory is "eem".
130	The EEM function provides these attributes in its function directory:
131	
132		ifname		- network device interface name associated with this
133				function instance
134		qmult		- queue length multiplier for high and super speed
135		host_addr	- MAC address of host's end of this
136				Ethernet over USB link
137		dev_addr	- MAC address of device's end of this
138				Ethernet over USB link
139	
140	and after creating the functions/eem.<instance name> they contain default
141	values: qmult is 5, dev_addr and host_addr are randomly selected.
142	Except for ifname they can be written to until the function is linked to a
143	configuration. The ifname is read-only and contains the name of the interface
144	which was assigned by the net core, e. g. usb0.
145	
146	Testing the EEM function
147	------------------------
148	
149	Configure IP addresses of the device and the host. Then:
150	
151	On the device: ping <host's IP>
152	On the host: ping <device's IP>
153	
154	5. FFS function
155	===============
156	
157	The function is provided by usb_f_fs.ko module.
158	
159	Function-specific configfs interface
160	------------------------------------
161	
162	The function name to use when creating the function directory is "ffs".
163	The function directory is intentionally empty and not modifiable.
164	
165	After creating the directory there is a new instance (a "device") of FunctionFS
166	available in the system. Once a "device" is available, the user should follow
167	the standard procedure for using FunctionFS (mount it, run the userspace
168	process which implements the function proper). The gadget should be enabled
169	by writing a suitable string to usb_gadget/<gadget>/UDC.
170	
171	Testing the FFS function
172	------------------------
173	
174	On the device: start the function's userspace daemon, enable the gadget
175	On the host: use the USB function provided by the device
176	
177	6. HID function
178	===============
179	
180	The function is provided by usb_f_hid.ko module.
181	
182	Function-specific configfs interface
183	------------------------------------
184	
185	The function name to use when creating the function directory is "hid".
186	The HID function provides these attributes in its function directory:
187	
188		protocol	- HID protocol to use
189		report_desc	- data to be used in HID reports, except data
190				passed with /dev/hidg<X>
191		report_length	- HID report length
192		subclass	- HID subclass to use
193	
194	For a keyboard the protocol and the subclass are 1, the report_length is 8,
195	while the report_desc is:
196	
197	$ hd my_report_desc
198	00000000  05 01 09 06 a1 01 05 07  19 e0 29 e7 15 00 25 01  |..........)...%.|
199	00000010  75 01 95 08 81 02 95 01  75 08 81 03 95 05 75 01  |u.......u.....u.|
200	00000020  05 08 19 01 29 05 91 02  95 01 75 03 91 03 95 06  |....).....u.....|
201	00000030  75 08 15 00 25 65 05 07  19 00 29 65 81 00 c0     |u...%e....)e...|
202	0000003f
203	
204	Such a sequence of bytes can be stored to the attribute with echo:
205	
206	$ echo -ne \\x05\\x01\\x09\\x06\\xa1.....
207	
208	Testing the HID function
209	------------------------
210	
211	Device:
212	- create the gadget
213	- connect the gadget to a host, preferably not the one used
214	to control the gadget
215	- run a program which writes to /dev/hidg<N>, e.g.
216	a userspace program found in Documentation/usb/gadget_hid.txt:
217	
218	$ ./hid_gadget_test /dev/hidg0 keyboard
219	
220	Host:
221	- observe the keystrokes from the gadget
222	
223	7. LOOPBACK function
224	====================
225	
226	The function is provided by usb_f_ss_lb.ko module.
227	
228	Function-specific configfs interface
229	------------------------------------
230	
231	The function name to use when creating the function directory is "Loopback".
232	The LOOPBACK function provides these attributes in its function directory:
233	
234		qlen		- depth of loopback queue
235		bulk_buflen	- buffer length
236	
237	Testing the LOOPBACK function
238	-----------------------------
239	
240	device: run the gadget
241	host: test-usb (tools/usb/testusb.c)
242	
243	8. MASS STORAGE function
244	========================
245	
246	The function is provided by usb_f_mass_storage.ko module.
247	
248	Function-specific configfs interface
249	------------------------------------
250	
251	The function name to use when creating the function directory is "mass_storage".
252	The MASS STORAGE function provides these attributes in its directory:
253	files:
254	
255		stall		- Set to permit function to halt bulk endpoints.
256				Disabled on some USB devices known not to work
257				correctly. You should set it to true.
258		num_buffers	- Number of pipeline buffers. Valid numbers
259				are 2..4. Available only if
260				CONFIG_USB_GADGET_DEBUG_FILES is set.
261	
262	and a default lun.0 directory corresponding to SCSI LUN #0.
263	
264	A new lun can be added with mkdir:
265	
266	$ mkdir functions/mass_storage.0/partition.5
267	
268	Lun numbering does not have to be continuous, except for lun #0 which is
269	created by default. A maximum of 8 luns can be specified and they all must be
270	named following the <name>.<number> scheme. The numbers can be 0..8.
271	Probably a good convention is to name the luns "lun.<number>",
272	although it is not mandatory.
273	
274	In each lun directory there are the following attribute files:
275	
276		file		- The path to the backing file for the LUN.
277				Required if LUN is not marked as removable.
278		ro		- Flag specifying access to the LUN shall be
279				read-only. This is implied if CD-ROM emulation
280				is enabled as well as when it was impossible
281				to open "filename" in R/W mode.
282		removable	- Flag specifying that LUN shall be indicated as
283				being removable.
284		cdrom		- Flag specifying that LUN shall be reported as
285				being a CD-ROM.
286		nofua		- Flag specifying that FUA flag
287				in SCSI WRITE(10,12)
288	
289	Testing the MASS STORAGE function
290	---------------------------------
291	
292	device: connect the gadget, enable it
293	host: dmesg, see the USB drives appear (if system configured to automatically
294	mount)
295	
296	9. MIDI function
297	================
298	
299	The function is provided by usb_f_midi.ko module.
300	
301	Function-specific configfs interface
302	------------------------------------
303	
304	The function name to use when creating the function directory is "midi".
305	The MIDI function provides these attributes in its function directory:
306	
307		buflen		- MIDI buffer length
308		id		- ID string for the USB MIDI adapter
309		in_ports	- number of MIDI input ports
310		index		- index value for the USB MIDI adapter
311		out_ports	- number of MIDI output ports
312		qlen		- USB read request queue length
313	
314	Testing the MIDI function
315	-------------------------
316	
317	There are two cases: playing a mid from the gadget to
318	the host and playing a mid from the host to the gadget.
319	
320	1) Playing a mid from the gadget to the host
321	host)
322	
323	$ arecordmidi -l
324	 Port    Client name                      Port name
325	 14:0    Midi Through                     Midi Through Port-0
326	 24:0    MIDI Gadget                      MIDI Gadget MIDI 1
327	$ arecordmidi -p 24:0 from_gadget.mid
328	
329	gadget)
330	
331	$ aplaymidi -l
332	 Port    Client name                      Port name
333	 20:0    f_midi                           f_midi
334	
335	$ aplaymidi -p 20:0 to_host.mid
336	
337	2) Playing a mid from the host to the gadget
338	gadget)
339	
340	$ arecordmidi -l
341	 Port    Client name                      Port name
342	 20:0    f_midi                           f_midi
343	
344	$ arecordmidi -p 20:0 from_host.mid
345	
346	host)
347	
348	$ aplaymidi -l
349	 Port    Client name                      Port name
350	 14:0    Midi Through                     Midi Through Port-0
351	 24:0    MIDI Gadget                      MIDI Gadget MIDI 1
352	
353	$ aplaymidi -p24:0 to_gadget.mid
354	
355	The from_gadget.mid should sound identical to the to_host.mid.
356	The from_host.id should sound identical to the to_gadget.mid.
357	
358	MIDI files can be played to speakers/headphones with e.g. timidity installed
359	
360	$ aplaymidi -l
361	 Port    Client name                      Port name
362	 14:0    Midi Through                     Midi Through Port-0
363	 24:0    MIDI Gadget                      MIDI Gadget MIDI 1
364	128:0    TiMidity                         TiMidity port 0
365	128:1    TiMidity                         TiMidity port 1
366	128:2    TiMidity                         TiMidity port 2
367	128:3    TiMidity                         TiMidity port 3
368	
369	$ aplaymidi -p 128:0 file.mid
370	
371	MIDI ports can be logically connected using the aconnect utility, e.g.:
372	
373	$ aconnect 24:0 128:0 # try it on the host
374	
375	After the gadget's MIDI port is connected to timidity's MIDI port,
376	whatever is played at the gadget side with aplaymidi -l is audible
377	in host's speakers/headphones.
378	
379	10. NCM function
380	================
381	
382	The function is provided by usb_f_ncm.ko module.
383	
384	Function-specific configfs interface
385	------------------------------------
386	
387	The function name to use when creating the function directory is "ncm".
388	The NCM function provides these attributes in its function directory:
389	
390		ifname		- network device interface name associated with this
391				function instance
392		qmult		- queue length multiplier for high and super speed
393		host_addr	- MAC address of host's end of this
394				Ethernet over USB link
395		dev_addr	- MAC address of device's end of this
396				Ethernet over USB link
397	
398	and after creating the functions/ncm.<instance name> they contain default
399	values: qmult is 5, dev_addr and host_addr are randomly selected.
400	Except for ifname they can be written to until the function is linked to a
401	configuration. The ifname is read-only and contains the name of the interface
402	which was assigned by the net core, e. g. usb0.
403	
404	Testing the NCM function
405	------------------------
406	
407	Configure IP addresses of the device and the host. Then:
408	
409	On the device: ping <host's IP>
410	On the host: ping <device's IP>
411	
412	11. OBEX function
413	=================
414	
415	The function is provided by usb_f_obex.ko module.
416	
417	Function-specific configfs interface
418	------------------------------------
419	
420	The function name to use when creating the function directory is "obex".
421	The OBEX function provides just one attribute in its function directory:
422	
423		port_num
424	
425	The attribute is read-only.
426	
427	There can be at most 4 ACM/generic serial/OBEX ports in the system.
428	
429	Testing the OBEX function
430	-------------------------
431	
432	On device: seriald -f /dev/ttyGS<Y> -s 1024
433	On host: serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
434	             -t<out endpoint addr> -r<in endpoint addr>
435	
436	where seriald and serialc are Felipe's utilities found here:
437	
438	https://github.com/felipebalbi/usb-tools.git master
439	
440	12. PHONET function
441	===================
442	
443	The function is provided by usb_f_phonet.ko module.
444	
445	Function-specific configfs interface
446	------------------------------------
447	
448	The function name to use when creating the function directory is "phonet".
449	The PHONET function provides just one attribute in its function directory:
450	
451		ifname		- network device interface name associated with this
452				function instance
453	
454	Testing the PHONET function
455	---------------------------
456	
457	It is not possible to test the SOCK_STREAM protocol without a specific piece
458	of hardware, so only SOCK_DGRAM has been tested. For the latter to work,
459	in the past I had to apply the patch mentioned here:
460	
461	http://www.spinics.net/lists/linux-usb/msg85689.html
462	
463	These tools are required:
464	
465	git://git.gitorious.org/meego-cellular/phonet-utils.git
466	
467	On the host:
468	
469	$ ./phonet -a 0x10 -i usbpn0
470	$ ./pnroute add 0x6c usbpn0
471	$./pnroute add 0x10 usbpn0
472	$ ifconfig usbpn0 up
473	
474	On the device:
475	
476	$ ./phonet -a 0x6c -i upnlink0
477	$ ./pnroute add 0x10 upnlink0
478	$ ifconfig upnlink0 up
479	
480	Then a test program can be used:
481	
482	http://www.spinics.net/lists/linux-usb/msg85690.html
483	
484	On the device:
485	
486	$ ./pnxmit -a 0x6c -r
487	
488	On the host:
489	
490	$ ./pnxmit -a 0x10 -s 0x6c
491	
492	As a result some data should be sent from host to device.
493	Then the other way round:
494	
495	On the host:
496	
497	$ ./pnxmit -a 0x10 -r
498	
499	On the device:
500	
501	$ ./pnxmit -a 0x6c -s 0x10
502	
503	13. RNDIS function
504	==================
505	
506	The function is provided by usb_f_rndis.ko module.
507	
508	Function-specific configfs interface
509	------------------------------------
510	
511	The function name to use when creating the function directory is "rndis".
512	The RNDIS function provides these attributes in its function directory:
513	
514		ifname		- network device interface name associated with this
515				function instance
516		qmult		- queue length multiplier for high and super speed
517		host_addr	- MAC address of host's end of this
518				Ethernet over USB link
519		dev_addr	- MAC address of device's end of this
520				Ethernet over USB link
521	
522	and after creating the functions/rndis.<instance name> they contain default
523	values: qmult is 5, dev_addr and host_addr are randomly selected.
524	Except for ifname they can be written to until the function is linked to a
525	configuration. The ifname is read-only and contains the name of the interface
526	which was assigned by the net core, e. g. usb0.
527	
528	Testing the RNDIS function
529	--------------------------
530	
531	Configure IP addresses of the device and the host. Then:
532	
533	On the device: ping <host's IP>
534	On the host: ping <device's IP>
535	
536	14. SERIAL function
537	===================
538	
539	The function is provided by usb_f_gser.ko module.
540	
541	Function-specific configfs interface
542	------------------------------------
543	
544	The function name to use when creating the function directory is "gser".
545	The SERIAL function provides just one attribute in its function directory:
546	
547		port_num
548	
549	The attribute is read-only.
550	
551	There can be at most 4 ACM/generic serial/OBEX ports in the system.
552	
553	Testing the SERIAL function
554	---------------------------
555	
556	On host: insmod usbserial
557		 echo VID PID >/sys/bus/usb-serial/drivers/generic/new_id
558	On host: cat > /dev/ttyUSB<X>
559	On target: cat /dev/ttyGS<Y>
560	
561	then the other way round
562	
563	On target: cat > /dev/ttyGS<Y>
564	On host: cat /dev/ttyUSB<X>
565	
566	15. SOURCESINK function
567	=======================
568	
569	The function is provided by usb_f_ss_lb.ko module.
570	
571	Function-specific configfs interface
572	------------------------------------
573	
574	The function name to use when creating the function directory is "SourceSink".
575	The SOURCESINK function provides these attributes in its function directory:
576	
577		pattern		- 0 (all zeros), 1 (mod63), 2 (none)
578		isoc_interval	- 1..16
579		isoc_maxpacket	- 0 - 1023 (fs), 0 - 1024 (hs/ss)
580		isoc_mult	- 0..2 (hs/ss only)
581		isoc_maxburst	- 0..15 (ss only)
582		bulk_buflen	- buffer length
583		bulk_qlen	- depth of queue for bulk
584		iso_qlen	- depth of queue for iso
585	
586	Testing the SOURCESINK function
587	-------------------------------
588	
589	device: run the gadget
590	host: test-usb (tools/usb/testusb.c)
591	
592	
593	16. UAC1 function (legacy implementation)
594	=================
595	
596	The function is provided by usb_f_uac1_legacy.ko module.
597	
598	Function-specific configfs interface
599	------------------------------------
600	
601	The function name to use when creating the function directory
602	is "uac1_legacy".
603	The uac1 function provides these attributes in its function directory:
604	
605		audio_buf_size - audio buffer size
606		fn_cap - capture pcm device file name
607		fn_cntl - control device file name
608		fn_play - playback pcm device file name
609		req_buf_size - ISO OUT endpoint request buffer size
610		req_count - ISO OUT endpoint request count
611	
612	The attributes have sane default values.
613	
614	Testing the UAC1 function
615	-------------------------
616	
617	device: run the gadget
618	host: aplay -l # should list our USB Audio Gadget
619	
620	17. UAC2 function
621	=================
622	
623	The function is provided by usb_f_uac2.ko module.
624	
625	Function-specific configfs interface
626	------------------------------------
627	
628	The function name to use when creating the function directory is "uac2".
629	The uac2 function provides these attributes in its function directory:
630	
631		c_chmask - capture channel mask
632		c_srate - capture sampling rate
633		c_ssize - capture sample size (bytes)
634		p_chmask - playback channel mask
635		p_srate - playback sampling rate
636		p_ssize - playback sample size (bytes)
637		req_number - the number of pre-allocated request for both capture
638			     and playback
639	
640	The attributes have sane default values.
641	
642	Testing the UAC2 function
643	-------------------------
644	
645	device: run the gadget
646	host: aplay -l # should list our USB Audio Gadget
647	
648	This function does not require real hardware support, it just
649	sends a stream of audio data to/from the host. In order to
650	actually hear something at the device side, a command similar
651	to this must be used at the device side:
652	
653	$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &
654	
655	e.g.:
656	
657	$ arecord -f dat -t wav -D hw:CARD=UAC2Gadget,DEV=0 | \
658	aplay -D default:CARD=OdroidU3
659	
660	18. UVC function
661	================
662	
663	The function is provided by usb_f_uvc.ko module.
664	
665	Function-specific configfs interface
666	------------------------------------
667	
668	The function name to use when creating the function directory is "uvc".
669	The uvc function provides these attributes in its function directory:
670	
671		streaming_interval - interval for polling endpoint for data transfers
672		streaming_maxburst - bMaxBurst for super speed companion descriptor
673		streaming_maxpacket - maximum packet size this endpoint is capable of
674				      sending or receiving when this configuration is
675				      selected
676	
677	There are also "control" and "streaming" subdirectories, each of which contain
678	a number of their subdirectories. There are some sane defaults provided, but
679	the user must provide the following:
680	
681		control header - create in control/header, link from control/class/fs
682				and/or control/class/ss
683		streaming header - create in streaming/header, link from
684				streaming/class/fs and/or streaming/class/hs and/or
685				streaming/class/ss
686		format description - create in streaming/mjpeg and/or
687				streaming/uncompressed
688		frame description - create in streaming/mjpeg/<format> and/or in
689				streaming/uncompressed/<format>
690	
691	Each frame description contains frame interval specification, and each
692	such specification consists of a number of lines with an inverval value
693	in each line. The rules stated above are best illustrated with an example:
694	
695	# mkdir functions/uvc.usb0/control/header/h
696	# cd functions/uvc.usb0/control/header/h
697	# ln -s header/h class/fs
698	# ln -s header/h class/ss
699	# mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
700	# cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/360p/dwFrameInterval
701	666666
702	1000000
703	5000000
704	EOF
705	# cd $GADGET_CONFIGFS_ROOT
706	# mkdir functions/uvc.usb0/streaming/header/h
707	# cd functions/uvc.usb0/streaming/header/h
708	# ln -s ../../uncompressed/u
709	# cd ../../class/fs
710	# ln -s ../../header/h
711	# cd ../../class/hs
712	# ln -s ../../header/h
713	# cd ../../class/ss
714	# ln -s ../../header/h
715	
716	
717	Testing the UVC function
718	------------------------
719	
720	device: run the gadget, modprobe vivid
721	
722	# uvc-gadget -u /dev/video<uvc video node #> -v /dev/video<vivid video node #>
723	
724	where uvc-gadget is this program:
725	http://git.ideasonboard.org/uvc-gadget.git
726	
727	with these patches:
728	http://www.spinics.net/lists/linux-usb/msg99220.html
729	
730	host: luvcview -f yuv
731	
732	19. PRINTER function
733	====================
734	
735	The function is provided by usb_f_printer.ko module.
736	
737	Function-specific configfs interface
738	------------------------------------
739	
740	The function name to use when creating the function directory is "printer".
741	The printer function provides these attributes in its function directory:
742	
743		pnp_string	- Data to be passed to the host in pnp string
744		q_len		- Number of requests per endpoint
745	
746	Testing the PRINTER function
747	----------------------------
748	
749	The most basic testing:
750	
751	device: run the gadget
752	# ls -l /devices/virtual/usb_printer_gadget/
753	
754	should show g_printer<number>.
755	
756	If udev is active, then /dev/g_printer<number> should appear automatically.
757	
758	host:
759	
760	If udev is active, then e.g. /dev/usb/lp0 should appear.
761	
762	host->device transmission:
763	
764	device:
765	# cat /dev/g_printer<number>
766	host:
767	# cat > /dev/usb/lp0
768	
769	device->host transmission:
770	
771	# cat > /dev/g_printer<number>
772	host:
773	# cat /dev/usb/lp0
774	
775	More advanced testing can be done with the prn_example
776	described in Documentation/usb/gadget-printer.txt.
777	
778	
779	20. UAC1 function (virtual ALSA card, using u_audio API)
780	=================
781	
782	The function is provided by usb_f_uac1.ko module.
783	It will create a virtual ALSA card and the audio streams are simply
784	sinked to and sourced from it.
785	
786	Function-specific configfs interface
787	------------------------------------
788	
789	The function name to use when creating the function directory is "uac1".
790	The uac1 function provides these attributes in its function directory:
791	
792		c_chmask - capture channel mask
793		c_srate - capture sampling rate
794		c_ssize - capture sample size (bytes)
795		p_chmask - playback channel mask
796		p_srate - playback sampling rate
797		p_ssize - playback sample size (bytes)
798		req_number - the number of pre-allocated request for both capture
799			     and playback
800	
801	The attributes have sane default values.
802	
803	Testing the UAC1 function
804	-------------------------
805	
806	device: run the gadget
807	host: aplay -l # should list our USB Audio Gadget
808	
809	This function does not require real hardware support, it just
810	sends a stream of audio data to/from the host. In order to
811	actually hear something at the device side, a command similar
812	to this must be used at the device side:
813	
814	$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &
815	
816	e.g.:
817	
818	$ arecord -f dat -t wav -D hw:CARD=UAC1Gadget,DEV=0 | \
819	aplay -D default:CARD=OdroidU3
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