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

Nicola Berndt 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  
>> 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.
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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