Re: sw_params for a direct-ed(dmix) hw pcm

[sylvain.bertrand@gmail.com]

On Sat, Mar 28, 2020 at 04:34:01PM -0500, Pierre-Louis Bossart wrote:
> Using MONOTONIC_RAW is very nice on paper, until you realize you can't
> program a timer using the information. You can only read the timestamp and
> not really do much if you want to sleep/wait.
> 
> In practice, if you really really need super-precise information you'll get
> use rdtsc(), and apply you own formulas. And otherwise stick with MONOTONIC,
> it's rather unlikely you will ever notice the NTP changes. PulseAudio, CRAS
> and a number of Android HALs use MONOTONIC and nobody ever complained.

The pb is not about using monotonic_raw, the thing is: it is documented valid
to use it which I did as expected from a naive reading of the api documentation
and found those issues. I can reasonably believe it will be the case for any
new alsa programmer.

For my code, in the end, I think I'll use the best "audio timestamp" I can get
from the status ioctl for linear interpolation with ffmpeg timestamps.

But this is off topic here.

The topic is discussing how to fix this bug, since I had to dig a bit in alsa.
It appears to me the recursive fix might be a good way, since it is done for
other api functions, but I am not Jaroslav Kysela neither Takashi Iwai then far
from grasping all the details of alsa.

-- 
Sylvain