[alsa-devel] Problems with safe API and snd-cs46xx

[Raymond Yau]

do you  mean that the function cannot update the min and max value ?



    snd_pcm_hw_constraint_list(runtime, 0,
                   SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
                   &hw_constraints_period_sizes);


2009/9/7 Takashi Iwai <tiwai at suse.de>

> At Mon, 07 Sep 2009 14:29:15 +0100,
> Tony Vroon wrote:
> >
> > [1  <text/plain (quoted-printable)>]
> > On Mon, 2009-09-07 at 14:32 +0200, Takashi Iwai wrote:
> > > Hm, I don't know of "safe API"...
> >
> > It is described here:
> > http://0pointer.de/blog/projects/guide-to-sound-apis.html
> >
> > Should this be incomplete or otherwise incorrect it would be useful to
> > have a rebuttal.
>
> Thanks for the pointer.
>
> > > A small test case, preferably a short C program just to reproduce
> > > the problem would be really needed in such a case.  It's very hard to
> > > guess what's going on and what is actually wrong in the driver only
> > > from your problem description, because of no obvious debug logs.
> >
> > If it is anything like the Aureal Vortex bug, the minimum period size
> > doesn't make sense.
>
> Yes, cs46xx also sets the minimum bytes 1, and this can be the
> same problem as aureal driver.
>
> (BTW, this isn't exactly a driver "bug" -- if this word is meaning a
>  programming error.  periods_size = 1 is no invalid setup in theory.
>  But, it's rarely a sane setup in reality, so it should be fixed
>  to match with the real machines indeed.)
>
> > Unlike the older the ALSA plugin, the new ALSA-NG
> > plugin in Audacious opens the audio device with defaults and does not
> > attempt to set period sizes.
>
> Maybe a bit "safer" option would be to check the period min size and
> raise to a sane value as a workaround.
>
> Or, if the period size doesn't matter much but rather the buffer size
> is more important, you can first limit the buffer size as max.  Then
> call snd_pcm_hw_params().  Without this, the PCM core determines the
> period size first, then the buffer size.
>
>
> Takashi
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