[alsa-devel] Options for ASYNC feedback source in USB-audio gadget (USB OTG)?

[Pavel Hofman]

On Wed, Aug 28, 2019 at 5:17 PM Pavel Hofman <pavhofman at gmail.com> wrote:
> IMO some common time frame must be used. E.g. kernel time in nanoseconds.
>
> How about something like this:
>
> 1) the core PCM part of alsa driver would keep relative samplerate and
> present such value in proc/sysfs to userspace.
> the calculation something like:
> copied X sample frames in Y kernel nanosecs (for the last e.g. approx.
> 30 secs ), with nominal samplerate 48kHz. The value would be
> (10^9 * X frames/Y nanosecs) / 48000 Hz samplerate = e.g. 1.00001

Perhaps the relative throughput could be calculated in alsa-lib when
talking to the driver? It has the same information available.
Turned-on by some environment var, regular output to some /tmp file
named after the corresponding hw card. Or does please alsa-lib have
some existing debug output, similar to /proc/asound, apart of stderr?

I very much appreciate any comments. IMO this would be a very useful
improvement, there are lots of RPi projects which would benefit from
properly working USB-audio connectivity.

Thanks,

Pavel.