Re: Trigger Callback

[Lee Revell <rlrevell@joe-job.com>]

On Tue, 2006-08-01 at 20:48 +0100, Julien Bramary wrote:
> 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.

"PCM engine" refers to the hardware's PCM engine, not ALSA's.  It's 100%
device dependent - you need to consult the docs for your sound device to
determine how to start the PCM.

Lee


-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV