[alsa-devel] A question about period

[Yu-hsuan Hsu]

For example, we can set period_size 32 to one device. But the device
consumes 40 frames each time. Can we said it support period_size 32? I
found many devices have this situation.

On Fri, Aug 3, 2018 at 4:30 PM Takashi Iwai <tiwai at suse.de> wrote:

> On Fri, 03 Aug 2018 10:09:30 +0200,
> Yu-hsuan Hsu wrote:
> >
> > Thank for your answer!
> >
> > The other question is if we set period_size to N, but the frames it
> > consumes once is 5N.
>
> Then the assumption is wrong.  How the hardware can issue an IRQ at N
> consumption while it processes for 5N in once?
>
>
> Takashi
>
> > Can it said it supports period_size N? How do we check
> > whether the period_size can be set correctly?
> >
> > On Fri, Aug 3, 2018 at 3:31 PM Takashi Iwai <tiwai at suse.de> wrote:
> >
> > > On Fri, 03 Aug 2018 08:28:37 +0200,
> > > Yu-hsuan Hsu wrote:
> > > >
> > > > Hi all,
> > > >
> > > > I have a question about the period we set in hw_params. I found
> different
> > > > boards may have different explanations about it. I have two guesses
> about
> > > > its meaning.
> > > >
> > > > 1. The period_size is the size of each hardware's consumption. If we
> set
> > > > period size to N, the pcm will consume N frames each time.
> > > >
> > > > 2. The period_size is the size to control when hardware call
> interrupt.
> > > If
> > > > we set period size to N, the pcm consume frames in its step. When the
> > > > number of frames it consumes more than N, it will call interrupt.
> > >
> > > 2 is the correct answer.
> > >
> > >
> > > HTH,
> > >
> > > Takashi
> > >
> > > > We can use snd_pcm_avail function to check the real available frames
> in
> > > > the device. If guess 1 is correct, the size of consumption should be
> > > fixed.
> > > > Else, setting period_size is nothing to do with hardware's
> > > > consumption. I've checked some boards and found that each board has
> > > > different behavior (Most of them meet guess 2). I'm confuse which
> one is
> > > > correct. Thanks!
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> > > > Alsa-devel at alsa-project.org
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> > > >
> > >
> > [2  <text/html; UTF-8 (quoted-printable)>]
> >
>