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

Christian Morales Vega cmorve69 at yahoo.es
Fri Jun 6 21:54:22 CEST 2008

snd_pcm_avail_update() documentation says: "Using of this function is
useless for the standard read/write operations. Use it only for mmap
access. See to snd_pcm_delay."

snd_pcm_delay() documentation says: "Note this function does not
update the actual r/w pointer for applications. The function
snd_pcm_avail_update() have to be called before any begin+commit

My english is far from perfect, and so the problem can be that I
missunderstood the docs but:
1- "Using of this function"? Should not be "Use of this function"?
2- Is snd_pcm_avail_update() really useless when not using mmap?
I have a SB Live! where snd_pcm_delay() always returns the correct
value, without any need for snd_pcm_avail_update(). But the same code
in the same machine with an hda-intel AD1988 needs a call to
snd_pcm_avail_update() before snd_pcm_delay() to give the correct
result. Without it snd_pcm_delay() always returns the value that *was*
correct in the last snd_pcm_writei() call.

So should the "application frame position" be always updated, or only
in read/write operations? In the first case AD1988 fails, in the
second case perhaps SB Live! is making too mucho work ;-)

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