Trigger Callback

[Julien Bramary <julien.bramary@blueyonder.co.uk>]

I'm an Alsa beginner and I'm trying to write an alsa driver for an embedded dac on ARM.

>From Iwai's doc:

/* trigger callback */
static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
{
    switch (cmd) {
    case SNDRV_PCM_TRIGGER_START:
            // do something to start the PCM engine
            break;
    case SNDRV_PCM_TRIGGER_STOP:
            // do something to stop the PCM engine
            break;
    default:
            return -EINVAL;
    }
}

My question here is,
What are we supposed to do to start the PCM engine?
Because, I'm currently doing nothing, and yet it starts anyway...
I'd like to understand to have more control.



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