[ntp:questions] Very large offset and jitter values after reboot

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Aug 24 18:49:21 UTC 2008

Nicola Berndt wrote:
> I have now successfully set up my machine to use a usb-gpd-mouse to set 

Not a good idea.  USB serial ports have high latency and jitter and NMEA 
feeds also tend to have high jitter, as they are designed for 
navigation, not for time.  You need a PPS signal on an ISA or PCI serial 
port interface.

> the time. Strangely every time I reboot I get results like this, wich 
> settle down after a (not so short) while:
>      remote           refid      st t when poll reach   delay   offset  
> jitter
> ==============================================================================
>  GPS_NMEA(0)     .GPS.            0 l    9   64   37    0.000  -580.75 
> 3965.19

You've not had your first 8 samples yet.  You haven't actually had 
enough for ntpd to act on the data.  You can speed that up with iburst, 
but ntpd will still take a long time to get a very tight lock.  jitter 
will reduce as you get to the eight samples.  The good? think, is that 
you are more than 128ms out, so that ntpd will step the time, to zero 
the offset, once it gets enough samples.

> The problem is, that this takes rather long and the computer's job 
> actually is, to provide exact time outdoors right after booting..

It is possible to get within about 10ms in two or three minutes.

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