[alsa-devel] Will ALSA ever call _prepare or _hw_params while it's playing?

Timur Tabi timur at freescale.com
Wed May 21 17:56:50 CEST 2008

Clemens Ladisch wrote:
> Timur Tabi wrote:
>> I have an ASoC driver with a _hw_params, _prepare, and _trigger functions.  I've
>> recently discovered that I need to keep one of my devices disabled until
>> playback starts.
>> So I would like to know if ALSA will ever call _hw_params, _prepare, or _trigger
>> if playback or capture is currently in process, or will ALSA first call the
>> _trigger to stop/pause the driver.
> While a stream is running (after trigger with START), ALSA will only
> call the pointer or the trigger (STOP/PAUSE/SUSPEND) callbacks.

That's good.

> Different streams are not synchronized in any way.  (This also applies to
> the playback/capture streams of one card.)

Ah, I hadn't thought about that.  If I'm doing simultaneous capture and playback
through the same device, then I can't guarantee that it's disabled.  Argh.


Timur Tabi
Linux kernel developer at Freescale

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