I have this alsa driver related question (ALSA api)

trigger callback:

static int
snd_ac97_playback_trigger(struct snd_pcm_substream *substream, int cmd)
{
struct audio_stream *stream = substream->private_data;
int err = 0;

switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
// dma start function
break;
case SNDRV_PCM_TRIGGER_STOP:
// dma stop function
break;
default:
err = -EINVAL;
break;
}
return err;
}

when is SNDRV_PCM_TRIGGER_STOP triggered? when device (/dev/dsp) is closed? I'm having problems with understanding how to properly disable
my DMA engine (double buffered). Driver is working just fine except that
at the end, one extra period is played. Today I've discovered a bug in a pointer callback. when fixed, could solve the problem. But my most important question would be: if trigger callback can stop dma engine before another irq would happen? Because I just don't know how to detect last period (last buffer) in my alsa driver. I think that it isn't even possible?

regards,
Bojan M.

anyone here with background in writing alsa drivers?

I think (not 100% sure jet), fix to period callback helped!
And I've found out that "snd_pcm_elapsed" function calls period callback...

r. bojan m.

how can I trigger SNDRV_PCM_TRIGGER_STOP one period earlier?

if I need to play BUF0 and BUF1, I wan't SNDRV_PCM_TRIGGER_STOP to be triggered,
and wait there so that BUF1 would be played, than I would stop dma engine...

now I get this just after BUF1 was played, but then possibly some extra bytes could be played?!

r. bojan m.