Re: A question about period

[Yu-hsuan Hsu <yuhsuan@google.com>]

Thank for your answer!

The other question is if we set period_size to N, but the frames it
consumes once is 5N. 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@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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>