[alsa-devel] [PATCH 0/20] ASoC: rsnd: add Synchronous SRC and U/O error salvage support

[Kuninori Morimoto]

Hi Mark

Thank you for your feedback

> > 2nd "dynamic" rate convert which is this patch is used as revision.
> > I don't know detail of use case, but, according to HW team,
> > sound clock has small accidental error.
> > Because of this, if we used 48kHz sound in long term,
> > but, the real sound can be 48001 Hz or 47999 Hz or something like that.
> > So, if we use it without revision in long term, the sound will has
> > small noise. This will be problem for TV or radio (?).
> > Thus, sound player wants to revise it by "dynamic" rate convert.
> > I guess DPCM is good match for "static" rate convert, but not good
> > for "dynamic".
> 
> In general it should be fine for anything - the driver for the SoC
> shouldn't need to understand why the rates are being converted, it
> should let the system integration worry about picking the rates.  That
> way we can more easily make the frameworks smarter and get benefits over
> all machines.
> 
> Though having said that I'm a little confused as to what exactly this
> control is intended for - am I right in thinking that what's actually
> going on here is that something in userspace is measuring the actual
> measured rate and feeding that information back to the DSP for
> correction?  If that's the case that does seem reasonable but also like
> we ought to have a general control interface for it.

Yes, you are correct.
Actually, I don't know detail of this userspace.
(How does it measure actual rate)
But, message actual rate -> feedback to SoC is the purpose.
(if actual rate was slow -> clock up, actual rate was fast -> clock down)

Is this "general control interface" means
"implemented under framework, not drvier" ?

> Adding Tim and Pierre since they might have views if my guess is
> correct, I could be wrong though.


Best regards
---
Kuninori Morimoto