[alsa-devel] maintaining fixed latency between output and input?
clemens at ladisch.de
Fri Sep 26 08:33:19 CEST 2008
Aaron J. Grier wrote:
> what's the most straight-forward way to maintain fixed latency between
> output and input without sitting in loop and continuously checking
> snd_pcm_avail_update() for the output and input descriptors?
> I was originally going to use callbacks, but I've recently read that is
> not a good idea. poll() seems to be the reccomended method.
> I'm visualizing something like this:
> if (output_is_ready)
> /* write output buffer */
> /* do output-side housekeeping */
> if (input_is_ready)
> /* read input buffer */
> /* do input-side housekeeping */
> /* communicate with other threads */
This is exactly how a full-duplex application should be structured.
To communicate with other threads, you can use a pipe so that you have
a file descriptor that can be used with the poll().
> combining the output and input snd_pcm_t into a single descriptor list
> for poll() seems straight-forward, but can I pass this superset list to
> snd_pcm_poll_descriptors_revents() without it getting confused?
No, snd_pcm_poll_descriptors_revents() looks at the file descriptors of
a single device and returns the ready status of that device.
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