[ntp:questions] Very large offset and jitter values after reboot
nb at komeda-berlin.de
Sun Aug 24 22:48:44 UTC 2008
David Woolley schrieb:
> 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.
I konw, but setting up pps failed due to noise on my pps line, wich I
had not time to really investigate yet. There is a thread connected to
that some days earlier on this list. I need the nmea-time for now, in
order to get things started.. PPS will follow very soon..
>> 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.
Thx for the iburs hint, I will try that.
Still very strange is that offset, wich also occurs when using
network-server from a ntp-pool..
>> 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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