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

Lee Revell rlrevell at joe-job.com
Sat Jun 7 02:46:12 CEST 2008

On Fri, Jun 6, 2008 at 3:54 PM, Christian Morales Vega
<cmorve69 at yahoo.es> wrote:
> 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
> operation."
> 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"?

I would just say "This function is useless for...".

> 2- Is snd_pcm_avail_update() really useless when not using mmap?

The pcm.c example referenced right below that comment would indicate otherwise:


> 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 ;-)

Is this with the latest ALSA HG sources?

The SBLive driver is better working and more mature, so I'd presume it
to be correct.  Takashi-san?


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