[ntp:questions] Slow convergence of NTP with GPS/PPS

David Woolley david at ex.djwhome.demon.co.uk.invalid
Fri Oct 24 21:33:43 UTC 2008

David J Taylor wrote:
>   "Our application requires good time accuracy (better than 5ms) but it 
> also needs to get there quickly (as quickly as possible, but ideally 
> taking no more than about 15 minutes)."
> I would have thought that a GPS and NTP would have been able to achieve 
> that, at least with a current drift file.

Assuming default parameters and worst case initial error, and no PPS, it 
will start with an error of 128ms and take about 40 minutes before it 
crosses zero.  It will then overshoot, so, might take several cycles to 
settle within 5ms.  Using minpoll 4 may get it to cross zero within the 
15 minutes, but the overshoot may still violate the criteria.

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