[no subject]

> after 13 hours, it would take about 5 minutes to wander 20us?

Not it would not. chrony has measured it, and it is not that much.


> I would think it is a best-case calculation as it assumes a linear drift in 
> one direction.
> I practice it will probably wobble, and take less than 5 minutes to wander 
> 20us.

>
> Please note we are talking MICROseconds here.  Not MILLIseconds.  I don't 
> think
> many standard systems will remain within 20us for several hours if left 
> without sync.
> (it would likely require some TCXO clock option)

Sure they could. If the temp is constant, as you claim, that is main cause of
changes in drift rate.

>
>> 
>> 
>>> The Span indicated by sourcestats is 79 for the PPS source now, and 103m 
>>> for
>>> the network sources.
>>> Would that mean it drops the PPS after 79 seconds?  That would be fine.
>> 
>> No. You really need to think through what you want and what the time on 
>> your
>> server machine delivers. After all if the computer clock in your local 
>> machine
>> was and exact track of UTC always to atto seconds, and you used the GPS 
>> only
>> to make determine the intial offset determination then it would be silly to
>> throw away that source just because the pps had not been heard from.
>
> We are not interested in "time that is likely a good estimation". We require 
> accurate time and if

I am sorry, but nothing will give you "accurate time" Not even GPS. What it
can give you is an estimate of the time and the accuracy of that estimate.


> we do not have it, or do not have certainty about it, we need to shutdown our 
> application.
> So we require some monitoring.  Of course I can add monitoring of "sources" 
> or "sourcestats"
> to the monitoring of "tracking" that we currently do, and alert when "Reach" 
> of the PPS
> clock is zero.  That is probably our quickest solution.  However, I would 
> have expected this
> error condition (missing PPS pulses) to be somehow reflected in the 
> "tracking" output.

Why?


>
> Rob
>

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