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SubjectRe: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago board
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>>> ... Why only 240? That's the next logical question.
>>> If you have a clarification for it, it may be the rigid reason to
>>> introduce such a hw constraint.
>
>> According to Brent, the DSP is using 240 period regardless the
>> hw_param. If the period size is 256, DSP will read 256 samples each
>> time but only consume 240 samples until the ring buffer of DSP is
>> full. This behavior makes the samples in the ring buffer of kernel
>> consumed quickly.
>
>> Not sure whether the explanation is correct. Hi Brent, can you confirm it?
>
> This seems to be going round and round in circles. Userspace lets the
> kernel pick the period size, if the period size isn't 240 (or a multiple
> of it?) the DSP doesn't properly pay attention to that apparently due to
> internal hard coding in the DSP firmware which we can't change so the
> constraint logic needs to know about this DSP limitation - it seems like
> none of this is going to change without something new going into the
> mix? We at least need a new question to ask about the DSP firmware I
> think.

I just tested aplay -Dhw: on a Cyan Chromebook with the Ubuntu kernel
5.4, and I see no issues with the 240 sample period. Same with 432, 960,
9600, etc.

I also tried just for fun what happens with 256 samples, and I don't see
any underflows thrown either, so I am wondering what exactly the problem
is? Something's not adding up. I would definitively favor multiple of
1ms periods, since it's the only case that was productized, but there's
got to me something a side effect of how CRAS programs the hw_params.

root@chrx:~# aplay -Dhw:0,0 --period-size=240 --buffer-size=480 -v 1.wav
Playing WAVE '1.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Hardware PCM card 0 'chtmax98090' device 0 subdevice 0
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : S16_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 480
period_size : 240
period_time : 5000
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 240
period_event : 0
start_threshold : 480
stop_threshold : 480
silence_threshold: 0
silence_size : 0
boundary : 8646911284551352320
appl_ptr : 0
hw_ptr : 0

root@chrx:~# aplay -Dhw:0,0 --period-size=256 --buffer-size=512 -v 1.wav
Playing WAVE '1.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Hardware PCM card 0 'chtmax98090' device 0 subdevice 0
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : S16_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 512
period_size : 256
period_time : 5333
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 256
period_event : 0
start_threshold : 512
stop_threshold : 512
silence_threshold: 0
silence_size : 0
boundary : 4611686018427387904
appl_ptr : 0
hw_ptr : 0


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