Re: snd-usb-audio : issue sending "set sample freq"

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On Mon, Apr 22, 2013 at 20:44:40 +0200, Daniel Mack wrote:
> Also, the lsusb dumps don't contain a audio specific header descriptor,
> which normally looks like this:
> 
>         AudioControl Endpoint Descriptor:
>           bLength                 7
>           bDescriptorType        37
>           bDescriptorSubtype      1 (EP_GENERAL)
>           bmAttributes         0x01
>             Sampling Frequency
>           bLockDelayUnits         0 Undefined
>           wLockDelay              0 Undefined
> 
> And without the "Sampling Frequency" bit in bmAttributes, the driver
> will bail out early (clock.c):

I think it has the class specific endpoint descriptor, but it is in
front of the standard endpoint descriptor. From the 'lsusb -v':

       AudioStreaming Interface Descriptor:
         bLength                14
         bDescriptorType        36
         bDescriptorSubtype      2 (FORMAT_TYPE)
         bFormatType             1 (FORMAT_TYPE_I)
         bNrChannels             2
         bSubframeSize           2
         bBitResolution         16
         bSamFreqType            2 Discrete
         tSamFreq[ 0]        16000
         tSamFreq[ 1]        48000
       ** UNRECOGNIZED:  07 25 01 81 02 00 00
       Endpoint Descriptor:
         bLength                 9
         bDescriptorType         5
         bEndpointAddress     0x03  EP 3 OUT
         bmAttributes            1
           Transfer Type            Isochronous
           Synch Type               None
           Usage Type               Data
         wMaxPacketSize     0x00c0  1x 192 bytes
         bInterval               1
         bRefresh                0
         bSynchAddress           0

The UNRECOGNIZED bit matches the missing AudioControl endpoint
descriptor.

Even if this is against the specification, devices that does this is out
there. I have seen the same thing on a Sennheiser BTD-500, but that only
supports one frequency, so I didn't hit this problem.


Torstein

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