Re: Improving status timestamp accuracy

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 6/6/16 4:42 AM, Alan Young wrote:
> On 06/06/16 09:34, Takashi Iwai wrote:
>> On Sun, 05 Jun 2016 12:33:20 +0200,
>> Alan Young wrote:
>>> Regardless of what value of DMA_RESIDUE_GRANULARITY_xxx that a driver
>>> claims to support, it is not really defined how fine a burst might
>>> be. So the end result is, from the point of view of audio, that the
>>> resulting position obtained by the pointer() call is pretty
>>> inaccurate. Hence my proposal to attempt to improve the accuracy of
>>> the pcm_status() result given the above constraints.
>> Well, the subject appears misleading.  What you want isn't the audio
>> timestamp accuracy.  From API POV, the accurate position is calculated
>> via the (additional) delay.  So, what you want is rather the accurate
>> position delay accounting, and the audio timestamp is merely one of
>> the ways to achieve that.
>>
>
> Well, yes, you could put it that way. Whether an accurate delay,
> combined with the associated timestamp, or an accurate audio delay, I
> would have the data needed to track audio drift from wallclock time.

I probably need more coffee but how is this patch helping track audio v. 
wallclock drift? The additional precision is based on wallclock deltas...

>
> See my response to Raymond for more detail.
>
> Alan.
>
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