[alsa-devel] A question about period

[Yu-hsuan Hsu]

Sorry for my unclear question. The device usually provide the range of
period_size to us, such as 16 to 1024 (We can get it from
snd_pcm_hw_params_get_period_size_min and max). It means we can choose
period_size 16 for this hardware device. However, the device only consumes
40 frames at each time. It only issue IRQ after it consumes 40 frames. My
question is, whether it can support period_size 16 as it said? Or it need
to change the range of period_size it provides.

Thank you for your patience and assistance.

yuhsuan


On Fri, Aug 3, 2018 at 6:14 PM Takashi Iwai <tiwai at suse.de> wrote:

> On Fri, 03 Aug 2018 12:04:34 +0200,
> Yu-hsuan Hsu wrote:
> >
> > 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.
>
> The question remains: how can the hardware issue an IRQ of period size
> 32 while it can consume 40 frames at each time?
>
> As you asked in the first post, the period size is the size where the
> hardware notifies the update.  Your description above doesn't match
> with the definition...
>
>
> Takashi
>
> >
> > 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!
> > > > > > _______________________________________________
> > > > > > Alsa-devel mailing list
> > > > > > Alsa-devel at alsa-project.org
> > > > > > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> > > > > >
> > > > >
> > > > [2  <text/html; UTF-8 (quoted-printable)>]
> > > >
> > >
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> >
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