[alsa-devel] A question about period

[Yu-hsuan Hsu]

Got it! Thank you very much.
There are many drivers has this problem.

yuhsuan

On Sat, Aug 4, 2018 at 2:31 AM Takashi Iwai <tiwai at suse.de> wrote:

> On Fri, 03 Aug 2018 19:24:05 +0200,
> Yu-hsuan Hsu wrote:
> >
> > 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.
>
> In that case, allowing period_size = 16 is obviously wrong.
> The practical minimum of period size is 40.  This must be set up via
> either snd_pcm_hardware or some hw_constraints.
>
>
> Takashi
>
> >
> > 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!
> > > > > > > > _______________________________________________
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> > > > > > > >
> > > > > > >
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