From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clemens Ladisch <clemens@ladisch.de>
Subject: Re: Dummy module and sample rates
Date: Thu, 24 Sep 2015 20:40:00 +0200
Message-ID: <56044380.4030109@ladisch.de>
References: <56029069.60700@weiss.ch> <56039FF3.3030203@ladisch.de>
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To: Uli Franke <uli.franke@weiss.ch>, "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
List-Id: alsa-devel@alsa-project.org

Uli Franke wrote:
>>> I set the hw params sample rate to 44k1 without error, but a subsequent
>>> call of snd_pcm_start returns EPIPE.
>>
>> In theory, this error code is returned if you didn't write any samples
>> into the buffer before starting.

> T(snd_pcm_start(pcm));
>
> n = snd_pcm_writei(pcm,
> 	             buffer,
> 	             ARRAY_SIZE(buffer) / channels);

And indeed this code tries to start the device without any samples in
the buffer.

>>> When setting hw params sample rate to 4k this does not happen.

This appears to be an artifact of the resampler.

> 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.

To prevent the device from starting automatically, change the
start_threshold.


Regards,
Clemens