| Re: [chrony-users] 'fallbackdrift' and temporarily connected ref-clocks |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] 'fallbackdrift' and temporarily connected ref-clocks
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Wed, 22 Jul 2020 07:37:27 +0200
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On Tue, Jul 21, 2020 at 02:32:22PM -0600, simon@xxxxxxxxxxxxx wrote:
> I might still be confused, it seems that there may be a mode of operation
> between 'tracking' and 'fallback'.
> --
> tracking --loss_of_clock--> ????? --drift_time_out--> freewheel
> --
> I do understand that I can stay longer there (in ?????), but what's actually
> happening, and why is it better if there are no other clocks to correct the
> system?
I'm not sure I understand the question. The fallback drifts kick in
depending on the time of the last update of the clock. If it's
configured as '6 9', it would take 2^6 seconds after the last update
of the clock for the first "drift" to kick in. There is no special
state between them.
> You asked about requirements:
> For DIY LTC I would want a precision of < +-100us (when tracking clock) and
> a drift of < 1frame (+-15ms) in 8hrs
That's about 0.5 ppm maximum error. That might be tricky with an
ordinary computer clock.
> I did a longer test run and uploaded some zip-file here:
> https://github.com/x42/ltc-tools/issues/17#issuecomment-662027246