Re: PCM driver only plays tiny portion of clip

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

On Wed, 2006-03-01 at 19:40 +0000, Adrian McMenamin wrote:
> On Wed, 2006-03-01 at 14:31 -0500, Lee Revell wrote:
> 
> > > What happens next?
> > 
> > The app(s) waiting to output audio (sleeping in poll() or write()) will
> > be woken up and based on the value returned by the pointer callback
> > above, informed that there is space in the buffer and how much space
> > there is, and will then write the next chunk of frames, and go back to
> > sleep.  Then we go back to "Hardware triggers interrupt" above and the
> > process repeats.
> 
> But something in the alsa subsystem determines whether there is any
> space before waking the app, yes?
> 

Yes - the value returned by your pointer callback minus the last value
returned by your pointer callback determines how much space is left.  So
if the app is waiting to write 512 frames, the pointer was 256 at the
last interrupt, and the current pointer is 512, the app will not wake up
until the next interrupt because only 256 frames can be written.

> and when the app is woken alsa calls the trigger callback?
> 

No when the app is woken it writes the data to the buffer, and we're
done, until the next interrupt.

The trigger callback is only called when the PCM is stopped, started, or
paused.

Lee



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