| Re: [chrony-dev] SOCK refclock system time resolution |
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On Wed, Sep 13, 2023 at 15:52:26 +0200, Miroslav Lichvar wrote:
> On Wed, Sep 13, 2023 at 09:28:34AM -0400, Josef 'Jeff' Sipek wrote:
> > However, I also see that cooked_time (i.e., sys_ts+correction) is fed into
> > SPF_AccumulateSample as sample->time. Later on, combine_selected_samples
> > makes use of ->time to calculate various things. So, it looks like any
> > error due to ns->us truncation will affect the math here. At a glance, I
> > can't tell if the effect is so small that it can be ignored or if there is
> > any benefit to avoiding the [0,999] ns error.
>
> It's so small that it can be ignored. The time at which the offset was
> measured is not that important. The frequency error between the
> reference and current clock is minimized by the control loop, usually
> to less than a ppm. Even if it was 1000 ppm, over a 1 microsecond
> interval that would still make only 1 nanosecond of phase error. It's
> well hidden in the noise. The main purpose of that timestamp is
> detection of stale and out-of-order samples.
Makes sense. Thanks for the context.
Jeff.
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