[alsa-devel] Dummy module and sample rates

[Uli Franke]

>> I fiddled around with the Dummy module and it seems to be the thing
>> we're looking for. I observed a rather strange behavior though:
>>
>> I set the hw params sample rate to 44k1 without error, but a subsequent
>> call of snd_pcm_start returns EPIPE. When setting hw params sample rate
>> to 4k this does not happen.
> 
> In theory, this error code is returned if you didn't write any samples
> into the buffer before starting.
> 
> An underrun is possible too, but should be reported later AFAIK.
> Could you check if a larger buffer size helps?

I checked if this is actually an XRun, as this is the official error
code. But even recover didn't have any effect.

When I write samples before starting the stream, snd_pcm_start returns

   File descriptor in bad state (-77)

which is obvious as the state of the stream changes from PREPARED to
RUNNING.

I tried to increase the buffer but with no effect.

No error occurs when I just write samples and omit the snd_pcm_start. I
just read some examples and got the impression that this seems to be
common practice anyhow. But up to now all my ALSA interfacing programs
actively started the stream and I never had any similar effect.

You can find a small test program here:

http://460c9235de50fe3b.paste.se/

Regards,
Uli