Re: USB feature unit

[Tom Jewell <tcj@xxxxxxxxxxxxx>]

On 03/23/2015 12:37 AM, Clemens Ladisch wrote:

Tom Jewell wrote:

I'm trying to debug some code that implements a feature unit in an
(incoming) USB device, based on an AT32UC3B1256 controller.  The feature
unit contains only a volume control, for which the host requests and I
provide values for MAX, MIN, CUR, and RES.  The host then tries to set
RES to half the value I've set, even though the host has no business
playing with MAX, MIN, or RES in the device.

I don't know what the authors of the USB Audio Class definition were
thinking, but they defined the SET_RES request, and so made it the
host's business.

So I stall, as the USB audio spec says to do if the device is asked to
modify an unmodifiable quantity.  [...] With the stall, the host
repeats the SET_RES request ten times at the same value, half of what
I've defined RES to be.

Those repeats are a workaround for devices that timeout on some control
requests, but they should not be done for stalls.

The upshot is that when the feature unit shows up (e.g. in xfce4 mixer)
it's missing the slider; it just shows a mute button.

This has probably nothing to do with the SET_RES requests.

What are the outputs of "lsusb -v" and "amixer contents" for this
control?  Are there any error messages in the system log?


Regards,
Clemens

Sorry - 'business' was a very poor choice of words on my part, based on the USB audio spec's saying "The MIN, MAX, and RES attributes are usually not supported for the Set request." It was a frustrating moment when I couldn't understand why in fact RES was being requested.

Yes, you're right that the missing slider was unrelated; it was the result of my neglecting to put 'break' statements in a 'switch' statement, resulting in all four attributes being identical.  It's not surprising the slider didn't show up.

For completeness, here are the outputs of amixer -c 2 controls and lsusb -v:

############## amixer -c 2

numid=3,iface=MIXER,name='RCVR MONITOR ANALOG GAIN Capture Volume'
numid=4,iface=MIXER,name='RCVR MONITOR ANALOG GAIN Capture Volume',index=1
numid=1,iface=PCM,name='Capture Channel Map'
numid=2,iface=PCM,name='Playback Channel Map'




############## lsusb -v

Bus 007 Device 002: ID 6666:89ab Prototype product Vendor ID
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.10
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x6666 Prototype product Vendor ID
  idProduct          0x89ab
  bcdDevice            0.00
  iManufacturer           7 Gargoyle Extension SA
  iProduct                8 UC3B USB Audio Test 1
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          210
    bNumInterfaces          4
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      1 Control Device
      bInterfaceProtocol      0
      iInterface              0
      AudioControl Interface Descriptor:
        bLength                10
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdADC               1.00
        wTotalLength           65
        bInCollection           2
        baInterfaceNr( 0)       1
        baInterfaceNr( 1)       2
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             1
        wTerminalType      0x0602 Digital Audio Interface
        bAssocTerminal          0
        bNrChannels             2
        wChannelConfig     0x0003
          Left Front (L)
          Right Front (R)
        iChannelNames           0
        iTerminal               0
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             2
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bSourceID               5
        iTerminal               0
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             3
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bNrChannels             2
        wChannelConfig     0x0003
          Left Front (L)
          Right Front (R)
        iChannelNames           0
        iTerminal               0
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             4
        wTerminalType      0x0602 Digital Audio Interface
        bAssocTerminal          0
        bSourceID               3
        iTerminal               0
      AudioControl Interface Descriptor:
        bLength                13
        bDescriptorType        36
        bDescriptorSubtype      6 (FEATURE_UNIT)
        bUnitID                 5
        bSourceID               1
        bControlSize            2
        bmaControls( 0)      0x02
        bmaControls( 0)      0x00
          Volume Control
        bmaControls( 1)      0x02
        bmaControls( 1)      0x00
          Volume Control
        bmaControls( 2)      0x02
        bmaControls( 2)      0x00
          Volume Control
        iFeature                9 RCVR MONITOR ANALOG GAIN
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface              0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface              0
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           2
        bDelay                  0 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                11
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           2
        bBitResolution         16
        bSamFreqType            1 Discrete
        tSamFreq[ 0]        48000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x85  EP 5 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0100  1x 256 bytes
        bInterval               1
        bRefresh                0
        bSynchAddress           0
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x00
          bLockDelayUnits         0 Undefined
          wLockDelay              0 Undefined
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface              0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface              0
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           3
        bDelay                  0 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                11
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           2
        bBitResolution         16
        bSamFreqType            1 Discrete
        tSamFreq[ 0]        48000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x06  EP 6 OUT
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0100  1x 256 bytes
        bInterval               1
        bRefresh                0
        bSynchAddress           0
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x00
          bLockDelayUnits         0 Undefined
          wLockDelay              0 Undefined
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        3
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass    255 Vendor Specific Subclass
      bInterfaceProtocol    255 Vendor Specific Protocol
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval              10
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x04  EP 4 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
Device Status:     0x0001
  Self Powered

#######################

Thanks

Tom Jewell

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