On Sat, 27 Mar 2004, James Courtier-Dutton wrote:
> I want a sound card to work in full duplex.
> I also want the in and out directions in sample sync.
> I.E. The playback period size is 160. I have my code polling, so that it
> is executed once every 160 samples.
> How do I ensure that each time my code executed, there will be at least
> 160 samples ready to be captured?
>
> Is there some way to link the starting of playback and capture so that
> they start at exactly the same time. So, each time i play 160 samples, I
> will have 160 samples ready to capture. If there are only 159 samples
> ready to be captured, my application will fail.
1) set avail_min to 160 (sw_params)
2) set start_threshold to boundary (sw_params) to disable automatic start
3) link streams (snd_pcm_link)
4) prepare playback (write some data)
5) start manually both streams (snd_pcm_start), note when streams are
linked, this command should be called only once, the second stream
will be started automatically
6) wait for one period to be processed, if any stream is behind the other,
correct avail_min for the "master" stream and wait again
The reasons for which the playback and capture pointers might differ are:
1) two clock sources (two different cards)
2) bus/card FIFO issues
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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