[alsa-devel] maintaining fixed latency between output and input?

Aaron J. Grier agrier at poofygoof.com
Fri Sep 26 03:05:26 CEST 2008

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 could use separate threads for output and input, but then I have to
perform synchronization between them, marshal external requests between
the two threads, and make a lot more work for myself.

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 */

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?

  Aaron J. Grier | "Not your ordinary poofy goof." | agrier at poofygoof.com

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