[Bug 28622] alsa under pulseaudio no longer produce sound

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=28622

--- Comment #51 from Andrew Eikum <aeikum at codeweavers.com> 2012-10-01 10:05:38 CDT ---
(In reply to comment #50)
> o It's time to add and use:
> #define QUIRK_PULSE 1
> with make_handle_underrun_config:
> This->quirks |= QUIRK_PULSE;
> 

Yeah, maybe, but that's a separate issue. This is intended to work better with
how ALSA is intended to be used (unreliable timers, so don't rely on
avail_update() to determine buffer fullness). We want this behavior in all
cases.

> o if(err < 0 || alsa_period_us < period / 10)
> Formerly, the check err<0 followed snd_pcm_hw_params_set_period_time_near
> Now you have a larger cascade involving err<0.  Does it do what you want?
> 

Yeah, I got it a little confused. I'll review that entire sequence, thanks for
finding it.

> o AudioClient_Start
> +   if(This->dataflow == eRender){
> +      snd_pcm_avail_update(This->pcm_handle);
> What's the purpose of this? IIRC, PA's avail_update was unreliable before it
> had really started (or am I confusing that with OSS?).
> 

It's a leftover from when I tried to use snd_pcm_htimestamp(), which turned out
to be unusable. I'll remove it.

> o There are now 3 timers
> - CreatetimerQueue
> - gettimeofday
> - the ALSA device's timer
> None of these are sync'ed.  I doubt anybody can prove that the code works
> correctly in the long run.  That's my big conceptual gripe.
> 
> I too got the feeling that PA might behave when it's not fed too much data, but
> how to best achieve that without introducing clock skew issues?
> 

The biggest issue here is using gettimeofday() instead of snd_pcm_htimestamp().
With htimestamp(), the clock skew would be detected and corrected by the
while(diff > period) loop. Unfortunately htimestamp() is unusable. The nice
thing about gettimeofday() is that it will always work regardless of ALSA bugs,
so I wonder if it isn't worth just ignoring the clock skew issue and letting it
under/overrun on occasion.

I'd like to submit this patch very soon, but it would be nice to get
confirmation that it works from someone who has been having problems.

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