On Mon, 22 Mar 2004, James Courtier-Dutton wrote:
> Jaroslav Kysela wrote:
> >>
> >>So, when is a PCM ready?
> >>If a PCM is already in SND_PCM_STATE_RUNNING, when is snd_pcm_wait()
> >>supposed to return ?
> >
> >
> > When avail >= avail_min.
>
> 1) Does this depend on period size in any way?
> For example, if period size is 6000 frames, and I set avail_min to 2000
> frames, will snd_pcm_wait() return when avail=2000 or avail=6000 ?
> Another example, if persiod size is 1500, and I set avail_min to 2000,
> will snd_pcm_wait() return when avail=200 or avail=3000 (2*1500)?
Pointers are updated in the interrupt or when you call snd_pcm_hwsync()
or snd_pcm_delay().
> 2) Is snd_pcm_wait() a call that uses little or no CPU time, much like a
> poll?
snd_pcm_wait() uses poll().
> 3) It appears from the docs that I can set avail_min at any time, even
> in SND_PCM_STATE_RUNNING.
> commands to set it would be: -
> snd_pcm_sw_params_current(this->audio_fd, swparams);
> snd_pcm_sw_params_set_avail_min(this->audio_fd, swparams,
> new_avail_min_size);
> snd_pcm_sw_params(this->audio_fd, swparams);
>
> or is there a better way to do it while in SND_PCM_STATE_RUNNING ?
No, you may cache the sw_params structure.
> 4) If snd_pcm_wait() is waiting, and with another thread we change the
> avail_min value, will the snd_pcm_wait() use the new value, or is the
> new value only used on the next call to snd_pcm_wait()
The threshold will be used immediately.
> My current tests were not using the resampler. i.e. app using 48k, sound
> card using 48k. I will try some tests that would use the resampler.
Then I need more info how I can reproduce the bug.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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