Documentation/usb/gadget-testing.txt

   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