[alsa-devel] Some information about UsbPre2 UAC2 support

shal at free.fr shal at free.fr
Mon Jan 28 14:48:16 CET 2013

----- Mail original -----
> De: "Clemens Ladisch" <clemens at ladisch.de>
> À: alsa-devel at alsa-project.org
> Envoyé: Lundi 28 Janvier 2013 14:10:06
> Objet: Re: [alsa-devel] Some information about UsbPre2 UAC2 support
> shal at free.fr wrote:
> >>
> >> shal at free.fr wrote:
> > It's seems that the behavior of the sound card depends to the first
> > get_configuration() and keep it until powered.
> > I discovers that when I performs a reboot in order to test my
> > modified kernel : The sound card remains in UAC1.
> > I have to plug/unplug the sound card in order to have 2
> > configurations
> > descriptor for this device.
> That's strange; the get_descriptor request should be the same.

The scenario is :
- I used a standard kernel (with 64 as get_descriptor buffer size)
- I connect the sound card
- the sound card recognize the OS as a Windows and sends a UAC1 only configuration and keep this state for all get_configuration
- I reboot with modified kernel (with 65 as get_descriptor buffer size)
- The sound card already provides a UAC1 only configuration
- I plug/unplug the sound card (the UbsPre2 is usb powered)
- Now the sound card provides a UAC1+UAC2 configuration

> > A usb_reset() can be helpful, perhaps?
> Perhaps.

=> I will try this :
- standard usb core driver (revert my ugly patch on huc.c and generic.c)
- in the usb audio I will add a quirk for the vendor/product ID of my sound card
- I performed a usb_reset()
- I performed a get_descriptor using a usb_control() with 65 as buffer size
- I choose the 2nd configuration descriptor

There is any chance that it works ?

> > Perhaps, we can do the same thing that the ASIO driver.
> That's what I meant with the quirk.  (The first configuration does
> have
> endpoints for high sample rates, but these aren't marked as being
> compatible with either UAC 1 or 2.)

I will ask more information to the Sound Devices developper.


best regards,

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