[alsa-devel] What does snd_pcm_delay() actually return?
tiwai at suse.de
Fri Jun 13 18:48:06 CEST 2008
At Fri, 13 Jun 2008 18:38:53 +0200,
> At Fri, 13 Jun 2008 18:20:43 +0200 (CEST),
> Jaroslav Kysela wrote:
> > On Fri, 13 Jun 2008, Takashi Iwai wrote:
> > > The point is that the wake-up timing isn't defined as constant but via
> > > a timing queue (or a request queue). This is more suitable for
> > > pull-style apps like JACK. Which irq source is used doesn't matter.
> > But applications can use timers or any other wakeup source directly (for
> > example from video card interrupt) - thus I'm not sure if it's good to
> > complicate our API, again. If we remove period tied I/O operations and
> > assumptions in alsa-lib (thus we will do only byte-stream transfers), then
> > everything will be fine and possible.
> > Other option is to create such timing queues separately as complete new
> > API without integration to PCM API. Complex apps call poll() anyway.
> > Support this complex timing for read()/write() for simple apps does not
> > make much sense, I think.
> Well, you miss the point. Let me clarify some issues:
> - The timing queue is optional. As default, we assume the period
> model as is now.
> - The period model is internally driven as the automatic fill of
> constant periods to the timing queue.
> - The stream is handled as a byte-stream.
> - If apps wants another wakeup source, it's fine. This has nothing
> to do with wakeup of the sound driver, no? It's up to apps how to
> handle streams. We just provide the timing from our system.
> - What the timing queue affects is only the wake-up timing of
> poll/read/write. So, basically, no other API change is required
> (although a simpler API with combination of queue+read/write would
> be more helpful).
> - In my original implementation, periods become the sync points
> between the hardware position and the system timer. But, this can
> be optional.
And one thing forgotten.
- If this were so great, I'd have already pushed to the upstream.
But I didn't. So you can guess that it's no perfect solution.
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