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- Subject: Re: [chrony-dev] [PATCH] MacOS X - add drift removal
- From: Bryan Christianson <bryan@xxxxxxxxxxxxx>
- Date: Thu, 6 Aug 2015 04:57:43 +1200
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> On 6/08/2015, at 12:26 am, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
>
> That makes sense. The precompensation I was thinking was about moving
> the mean offset closer to zero. For example, if the clock has a drift
> of 100 ppm, the offset would be moving somewhere around around 0 +/-
> 50 microseconds, instead of 50 +/- 50 microseconds.
>
> Something like this (not tested):
>
> @@ -119,7 +119,7 @@ start_adjust(void)
> }
>
> UTI_DiffTimevalsToDouble(&elapsed, &T1, &T0);
> - accrued_error = elapsed * current_freq;
> + accrued_error = (elapsed + DRIFT_REMOVAL_INTERVAL / 2.0) * current_freq;
>
> adjust_required = - (accrued_error + offset_register);
This changes the effective drift (as seen in tracking.log) from 18ppm to 6ppm but System time still hovers around -10us
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