[alsa-devel] A question about period

[Takashi Iwai]

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!
> > > _______________________________________________
> > > Alsa-devel mailing list
> > > Alsa-devel at alsa-project.org
> > > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> > >
> >
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