[ntp:questions] Very large offset and jitter values after reboot
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
> 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
> GPS_NMEA(0) .GPS. 0 l 9 64 37 0.000 -580.75
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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