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

Richard B. Gilbert rgilbert88 at comcast.net
Fri Oct 24 14:24:41 UTC 2008


David J Taylor wrote:
> Richard B. Gilbert wrote:
> []
>> And ntpd could take many minutes to bludgeon the local clock into
>> submission!  It's easy to determine and set the correct time.  It's
>> less easy to determine and set the correct frequency and thus KEEP the
>> correct time.
> 
> Wasn't the OP looking for about 0.5s accuracy?  Ah, no, that was someone 
> else.  Here we're aiming for:
> 
>   "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.
> 
> Cheers,
> David 
> 
> 

Try it some time!  Ntpd makes a mad dash for zero offset, overshoots, 
and then "rings" for a while.  Eventually it gets that tight synch that 
we like to see but it does take about thirty minutes.

I think I mentioned this here at the time I observed it.  I believe that 
I also remarked that I could have done it a lot faster by hand if I had 
the "control knobs".




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