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@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@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.
- 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.
- 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@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
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