On Wed, 12 Aug 2020 16:46:40 +0200, Pierre-Louis Bossart wrote: > > > >>>>>> 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 What if with --period-size=256 --buffer-size=512 and --test-position? Can you reproduce the problem in your side? > 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? I also wonder what's really missing, too :) BTW, I took a look back at the thread, and CRAS seems using a very large buffer, namely: [ 52.434791] sound pcmC1D0p: PERIOD_SIZE [240:240] [ 52.434802] sound pcmC1D0p: BUFFER_SIZE [204480:204480] Takashi
