Re: PCM driver only plays tiny portion of clip

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

On Wed, 2006-03-01 at 14:59 -0500, Lee Revell wrote:
> 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.
> 

Presumably this is on the assumption that 512 frames is a period?





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