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

Richard B. Gilbert rgilbert88 at comcast.net
Tue Sep 30 22:31:48 UTC 2008

David Woolley wrote:
> Richard B. Gilbert wrote:
>> If you are using a recent version of ntpd, start it with the "-g" 
>> switch.  That will cause it to set the clock to the correct time once 
>> only!  If you have a good drift file, you should be synchronized in 
>> thirty seconds or so and be within ten milliseconds, or less, of the 
>> correct time.
> My understanding was that -g turns off the 1000 second check for the 
> first step, but still leaves the time within +/- 128ms, which will still 
> take an unacceptable time to converge to +/- 5ms.  Certainly the 4.2.4p4 
> documentation makes no claims for it beyond once only disabling the 1000 
> second check.

I don't recall that +/- 128ms is specified anywhere.  If ntpd gets it's 
initial time from a hardware reference clock, the time SHOULD be very 
close.  This will, off course, depend on the latencies in the reference 
clock's response and the resolution of the time supplied.

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