[LAU] Sound Devices USBPre2, UAC2 status

[shal at free.fr]

----- Mail original -----
> De: "Hans Wilmers" <hanswil at notam02.no>
> À: linux-audio-user at lists.linuxaudio.org
> Envoyé: Jeudi 10 Janvier 2013 23:23:56
> Objet: Re: [LAU] Sound Devices USBPre2, UAC2 status
> 
> On 01/10/2013 10:30 PM, shal at free.fr wrote:
> >
> >> De: "Hans Wilmers" <hanswil at notam02.no>
> >> No luck with this either - fastest one I get is 48000. This
> >> corresponds
> >> to the output of lsusb, which does not list samplerates over 48000
> >> for
> >> this device.
> >
> >
> > I have tried different kernel, 3.2 to 3.7.1, vanilla or ubuntu
> > kernel.
> >
> > The lsusb does not means that you are limited to 48000.
> >
> > The lsusb provides the "devices descriptor" and a devices
> > descriptors has one or more "configuration descriptor". The kernel
> > chooses one of the "configuration descriptor".
> > In your device descriptor (provided directly by the device) there
> > is two possibles configuration descriptons (the
> > bNumConfigurations=2). The first one corresponds to the UAC1 mode
> > in high-speed (this is my one configuration) and so limited to
> > 48000. The second one is the UAC2 mode (the expected mode).
> >
> > Perhaps the kernel choose the fist good one, so UAC1  .
> >
> > Can you send the result of  cat /proc/asound/USBPre2/stream0  ?
> >
> 
> Yes, see below.
> 
> / Hans
> 
> 
> --------------- /proc/asound/USBPre2/stream0 -------------
> 
> Sound Devices USBPre2 at usb-0000:00:1a.0-1.2, high speed : USB Audio
> 
> Playback:
>    Status: Stop
>    Interface 1
>      Altset 1
>      Format: S16_LE
>      Channels: 2
>      Endpoint: 6 OUT (ASYNC)
>      Rates: 8000, 16000, 24000, 32000, 44100, 48000
>      Data packet interval: 1000 us
>    Interface 1
>      Altset 2
>      Format: S24_3LE
>      Channels: 2
>      Endpoint: 6 OUT (ASYNC)
>      Rates: 8000, 16000, 24000, 32000, 44100, 48000
>      Data packet interval: 1000 us


Hi Hans,

So , effectively you are limited to 48000.
I supposed that the linux kernel chooses this first valid configuration descriptor.

This behavior can be modified in the kernel with adding a quirk in the code.
If my usbPre2 has the good device descripton, I can devlop and test this patch. 
But my devices does not offer the UAC2 configuration descriptor.

I have write a post on the Sound Devices Forum. Perhaps I will have help to understand why my device has this strange behavior and correct it.

In this case, I think I can patch the kernel to have the UAC2 mode...

Olivier