[PATCH 1/2] ALSA: usb-audio: Improve frames size computation

[Takashi Iwai]

On Fri, 24 Apr 2020 04:24:48 +0200,
Alexander Tsoy wrote:
> 
> For computation of the the next frame size current value of fs/fps and
> accumulated fractional parts of fs/fps are used, where values are stored
> in Q16.16 format. This is quite natural for computing frame size for
> asynchronous endpoints driven by explicit feedback, since in this case
> fs/fps is a value provided by the feedback endpoint and it's already in
> the Q format. If an error is accumulated over time, the device can
> adjust fs/fps value to prevent buffer overruns/underruns.
> 
> But for synchronous endpoints the accuracy provided by these computations
> is not enough. Due to accumulated error the driver periodically produces
> frames with incorrect size (+/- 1 audio sample).
> 
> This patch fixes this issue by implementing a different algorithm for
> frame size computation. It is based on accumulating of the remainders
> from division fs/fps and it doesn't accumulate errors over time. This
> new method is enabled for synchronous and adaptive playback endpoints.
> 
> Signed-off-by: Alexander Tsoy <alexander at tsoy.me>

Applied to for-next branch now.


thanks,

Takashi