[ntp:questions] Some anomalies

Vaidotas J. dtroit at ktu.lt
Mon Nov 29 09:17:25 UTC 2004


recently my office decided to create some QoS monitoring system and the main goal of it's correct results on some tests is precise time synchronization. So we bought few Trimble Acutime 2000 SyncKits and I've conected them at first to my WS and then to project notebook. It;s a little bit pitty, that (as far as i know), that Trimbles Palisade ref clock driver doesn't use ports B output also no PPS usage too ;(
But anyway, the synchronization is received and so on... After some time, i wrote this veeeery small c program to get the offset value from ntp_adjtime() function for one hour (calling it every 1 second). Here it is:
#include <sys/timex.h>
#include <sys/time.h>
#include <stdio.h>
int main(){
int i;
struct timeval ts;
struct timex *adjtm; //ntp_adjtime pointeris
adjtm = (struct timex *)malloc(sizeof(struct timex));
for (i=0;i<=3600;i++) {
printf("%i\t%i\n",i, (unsigned int) adjtm->offset);
} //foras
And i graphed some results enabling/disabling some kernel functions:
(gnuplot was used as a ploting engine, with just simple input x,y from file, generated by this smaaaal c program of mine:)

So in one graph we see that for sometime offset was 0, in some of the graphs (that are wildely absurd) the offset is taken just right after the ntpd is started and other graphs are commented.
The last graph I think is quite good and stable (that last jump is a mystery to me), but such offset with direct startum0 connected to PC isn't satisfieing. So maybe any ideas/responses to these graphs or some experience using Trimble GPS Acutime? What's the offset with Your Trimble Acutime and the settings of the system that runs it and other things. So if any ideas please help me to get the smallest ofset :) Because rigth now i've no more ideas :)

PS> The notebook is:
model name      : Intel(R) Pentium(R) 4 Mobile CPU 1.70GHz
System parameters:
Linux ippm 2.6.9 #4 Fri Nov 26 16:39:29 EET 2004 i686 GNU/Linux
Debian 3.1 distr.
System has no other processes than ntpd, apache, sshd and the GPS is connected via UST-RS232 converter (no comm port on this notebook).

Vaidotas J.
Network engineer,
dtroit at ktu.lt

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