The different STATES of ALSA

[Hynek Hanke <hanke@brailcom.org>]

Hi everyone,

I'm having very much troubles programming an ALSA interface because the
documentation is pretty poor. I'm very much confused about the different states
in alsa-lib.

(After I was told alsa-lib is not thread-safe and there is some bug in the kernel
implementation of the underlaying calls of snd_pcm_writei(), I'm now running the
non-blocking/polling approach).

My questions:

1) In which states am I allowed to call
	a) snd_pcm_hw_params_any
	b) snd_pcm_hw_params
	c) snd_pcm_prepare
	d) snd_pcm_drop and _drain

2) Which states do they bring me to, if they don't return an error?

3) How is it possible that snd_pcm_drain returns with a success value *and*
   the snd_pcm_state() still reports SND_PCM_STATE_DRAINING ? Is this a bug?

4) How is it possible, that the whole time a sound is played snd_pcm_writei()
   never returns the value -EPIPE and still, when checking the state before
   playing the next sound, I find the device in the SND_PCM_STATE_XRUN
   (snd_pcm_drain() gets called in the meantime).

The problems (3) and (4) seem to arrise only under some circumstances, possibly
when more sounds are played in a quick succession.

Thank you for help,
Hynek Hanke



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