[alsa-devel] snd_pcm_avail_update() needed before snd_pcm_delay() with hda-intel

[Christian Morales Vega]

2008/6/17 Takashi Iwai <tiwai at suse.de>:
> At Thu, 12 Jun 2008 20:32:51 +0200,
> Christian Morales Vega wrote:
>>
>> 2008/6/12 Takashi Iwai <tiwai at suse.de>:
>> > It's unlikely a driver issue but an incompatibility of dmix, I guess.
>> > But still I don't figure out why this happens.  The hwsync is done at
>> > each snd_pcm_dmix_delay() call (as long as slowptr is set, and it's so
>> > as default).  So, there shouldn't be any difference...
>> >
>> > What happens if you use "hw" or "plughw"?
>> With both plughw and hw works fine.
>>
>> If helps, I have simplified the problematic bsnes code into this:
>
> The program looks running fine on my machine with another HD-audio
> codec.  What is expected in the output and how wrong on yours?

I knew I should not put it under the code :-p
"The listened effect is that when fails you listen the noise for just
buffer_time, and when works the noise never ends."

So the output with the SB Live! is:
State: 2
Delay: 0
Passed
State: 2
Delay: 882
Passed
State: 2
Delay: 1764
Passed
State: 2
Delay: 2646
Passed
State: 2
Delay: 3528
Passed
State: 3
Delay: 4410
Delay/Goal: 4410/3528
State: 3
Delay: 4410
Delay/Goal: 4410/3528
State: 3
Delay: 4410
Delay/Goal: 4410/3528
State: 3
Delay: 4410
Delay/Goal: 4410/3528
State: 3
Delay: 4409
Delay/Goal: 4409/3528

and so until delay reaches 3528, when a new snd_pcm_writei() is done.

With the AD1988 the buffer is fulled one time. After that never again
reaches snd_pcm_writei(). The output is:
State: 2
Delay: 0
Passed
State: 2
Delay: 940
Passed
State: 2
Delay: 1880
Passed
State: 2
Delay: 2820
Passed
State: 2
Delay: 3760
Passed
State: 3
Delay: 4700
Delay/Goal: 4700/3764
State: 3
Delay: 4700
Delay/Goal: 4700/3764
State: 3
Delay: 4700
Delay/Goal: 4700/3764

and so. Delay never decreases. But after some time you see.
State: 4
Delay: 4700
Delay/Goal: 4700/3764

There has been an underrun even if appl_ptr is 4700 frames ahead of hw_ptr???
If you uncomment snd_pcm_avail_update() delay decreases and everything is ok.