[alsa-devel] Improving status timestamp accuracy

[Pierre-Louis Bossart]

On 6/7/16 2:44 AM, Alan Young wrote:
> On 06/06/16 15:53, Pierre-Louis Bossart wrote:
>> I probably need more coffee but how is this patch helping track audio
>> v. wallclock drift? The additional precision is based on wallclock
>> deltas...
>
>
> Of course, it wouldn't, due to being buggy. I think I needed more coffee
> too.
>
> But the basic point is that if the difference between tstamp and
> (trigger_tstamp + audio_tstamp) varies over time, this will be the drift
> between the audio output and wallclock time.

You want to track (tstamp - trigger_tstamp) v. (audio_tstamp - 
trigger_tstamp)

>
> Depending upon the specific goal, a calculation based on tstamp + delay
> may be appropriate.
>
> This is true today with a granularity of about period time. The idea
> behind my change is to make the granularity much smaller, preferably < ~1ms.
>
> I'll work on developing and testing a patch for consideration before
> coming back to the last. It will be easier to discuss the merits or
> otherwise of my proposal with a concrete, working patch to consider.
>
> Alan.
>