[alsa-devel] [PATCH v5] ALSA: usb: Work around CM6631 sample rate change bug

Daniel Mack zonque at gmail.com
Wed Mar 27 12:52:14 CET 2013

On 27.03.2013 12:47, Torstein Hegge wrote:
> On Wed, Mar 27, 2013 at 11:09:01 +0100, Clemens Ladisch wrote:
>> Torstein Hegge wrote:
>>> The C-Media CM6631 USB receiver doesn't respond to changes in sample rate
>>> while the interface is active. The same behavior is observed in other UAC2
>>> hardware like the VIA VT1731.
>> Might it be possible that these devices have reset the interface (see
>> UAC2 section 3.16.3), and that the driver hasn't noticed this because it
>> doesn't handle Active Alternate Setting Control interrupts?
> If that was the case, wouldn't the device be in altsetting zero after
> the sample rate set and not be able to output sound at all? And as long
> as the current altsetting supports the target sample rate as reported in
> /proc/asound/card1/stream0, Active Alternate Setting Control shouldn't
> have to be invoked.

You could just try and catch that currently unhandled interrupt. We
should support that anyway at some point ...


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