Messages in this thread | | | Subject | Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago board | From | Pierre-Louis Bossart <> | Date | Wed, 12 Aug 2020 09:46:40 -0500 |
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>>>>>> After doing some experiments, I think I can identify the problem more precisely. >>>>>> 1. aplay can not reproduce this issue because it writes samples >>>>>> immediately when there are some space in the buffer. However, you can >>>>>> add --test-position to see how the delay grows with period size 256. >>>>>>> aplay -Dhw:1,0 --period-size=256 --buffer-size=480 /dev/zero -d 1 -f dat --test-position >>>>>> Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 >>>>>> Hz, Stereo >>>>>> Suspicious buffer position (1 total): avail = 0, delay = 2064, buffer = 512 >>>>>> Suspicious buffer position (2 total): avail = 0, delay = 2064, buffer = 512 >>>>>> Suspicious buffer position (3 total): avail = 0, delay = 2096, buffer = 512 >>>>>> ... >>>>> >>>>> Isn't this about the alignment of the buffer size against the period >>>>> size, not the period size itself? i.e. in the example above, the >>>>> buffer size isn't a multiple of period size, and DSP can't handle if >>>>> the position overlaps the buffer size in a half way. >>>>> >>>>> If that's the problem (and it's an oft-seen restriction), the right >>>>> constraint is >>>>> snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS); >>>>> >>>>> >>>>> Takashi >>>> Oh sorry for my typo. The issue happens no matter what buffer size is >>>> set. Actually, even if I want to set 480, it will change to 512 >>>> automatically. >>>> Suspicious buffer position (1 total): avail = 0, delay = 2064, buffer >>>> = 512 <-this one is the buffer size >>> >>> OK, then it means that the buffer size alignment is already in place. >>> >>> And this large delay won't happen if you use period size 240? >>> >>> >>> Takashi >> Yes! If I set the period size to 240, it will not print "Suspicious >> buffer position ..." > > So it sounds like DSP handles the delay report incorrectly. > Then it comes to another question: the driver supports both SOF and > SST. Is there the behavior difference between both DSPs wrt this > delay issue?
I still don't get what the issue is. The two following cases work fine with the SST/Atom driver:
root@chrx:~# aplay -Dhw:0,0 --period-size=240 --buffer-size=480 /dev/zero -d 2 -f dat --test-position Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo root@chrx:~# aplay -Dhw:0,0 --period-size=960 --buffer-size=4800 /dev/zero -d 2 -f dat --test-position Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
The existing code has this:
/* Make sure, that the period size is always even */ snd_pcm_hw_constraint_step(substream->runtime, 0, SNDRV_PCM_HW_PARAM_PERIODS, 2);
return snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
and with the addition of period size being a multiple of 1ms all requirements should be met?
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