[alsa-devel] How to use implicit feedback with full duplex?

Clemens Ladisch clemens at ladisch.de
Wed Feb 6 21:13:29 CET 2013

Eldad Zack wrote:
> On Tue, 5 Feb 2013, Clemens Ladisch wrote:
>> I thought I'd try to use implicit feedback with my simple audio device:
>> [...]
>> This works fine when playing something:
> ...
>> But when I then try to record at the same time, the driver refuses to
>> configure the input endpoint (to the only format, which is already set):
>> And despite that "alreay in use" check, the input endpoint is affected
>> so much that playback breaks.
>> Is full duplex supposed to work?  Does it work with other devices?
> This is probably a "yes, but" :)
> I use my device mostly full duplex, but with jack opening both
> playback and capture at the same time.
> I assume you are opening two different streams, one for playback and
> one for capture.

Jack *also* uses two different streams, but it opens them at the same

> Can you try using jackd -d alsa -d hw:x with the device and see if that
> works for you?

That works.  This means that there is a race condition in the driver, or
that the different open/hw_params/prepare order trips it up.

Anyway, I feel safe now to enable implicit feedback for other devices.


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