Re: snd_pcm_wait() More details required.

[James Courtier-Dutton <James@superbug.demon.co.uk>]

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)?

2) Is snd_pcm_wait() a call that uses little or no CPU time, much like a 
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 ?

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()

> 
> 
>>I have discovered a problem with xine when using it. I have done a work 
>>around in xine so that dmix now works in xine. I think that my 
>>assumptions regarding snd_pcm_wait() might have been wrong, so I want to 
>>  get accurate details from yourselves.
>>It also might be a good idea to update the documentation for 
>>snd_pcm_wait() with more details.
> 
> 
> We had a bug in the resample plugin which causes that snd_pcm_wait() 
> function was broken. Try alsa-lib from CVS.

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.

> 
> 						Jaroslav
> 



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