[alsa-devel] underruns and strange code in pcm_rate.c (and patch)

[Takashi Iwai]

At Tue, 06 Nov 2007 14:47:38 +0000,
James Courtier-Dutton wrote:
> 
> Takashi Iwai wrote:
> > removing the hack there.  Maybe not.  But, I feel it's a barren
> > discussion.  It's really a design problem.  Sigh.
> > 
> 
> Are any steps being taken to change the design so that sample rate
> conversion works better?
> The options are:
> 1) get the sound card hardware to produce time based interrupts for the
> rate plugin to use as it's period trigger. This is how the old OSS
> drivers did it.

It's not neccessarily to be a sound card that generates interrupts.
It can be simply an any timer.  We have a hrtimer now, so the material
to cook is there.  We need an exact synchronization, though, for
example with the timing correction a la PLL.

> 2) allow the user application to use different buffer/period sizes than
> the hardware itself.

This is the best option, together with an arbitrary interrupt source.

> 3) Try to encourage applications not to use the pcm_rate plugin at
> all!!!  Instead force each application to do its own sample rate
> conversion to match what the hardware can do.

No, this cannot be accepted in the current situation.  It's 100 steps
backward.  If we really do this, we should get rid of the whole
plugins and provide only very bare stuff.  That is, it'd be better to
re-design the whole ALSA API from scratch.


Takashi