On Tue, Aug 11, 2020 at 05:35:45PM +0800, Yu-Hsuan Hsu wrote:
Takashi Iwai tiwai@suse.de 於 2020年8月11日 週二 下午4:39寫道：
... 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.