On 11/29/2011 1:42 PM, Pete Ashdown wrote:
Running with an Oncore GPS& a TAPR TAC. If I "ntpdate -b" a nearby
synchronized server before I start ntpd, the offsets initially look pretty
good:
remote refid st t when poll reach delay offset jitter
==============================================================================
GPS_ONCORE(0) .GPS. 0 l - 16 0 0.000 0.000 0.000
time-C.timefreq .ACTS. 1 u 39 64 1 37.534 -11.785 0.001
ntp-nasa.arc.na .GPS. 1 u 38 64 1 19.868 -0.948 0.001
As time goes on, things start to get crazier:
remote refid st t when poll reach delay offset jitter
==============================================================================
xGPS_ONCORE(0) .GPS. 0 l 6 16 377 0.000 -999.97 0.003
time-C.timefreq .ACTS. 1 u 50 64 3 37.370 -16011. 0.080
ntp-nasa.arc.na .GPS. 1 u 52 64 3 19.823 -16000. 0.046
More time with 100% reachability:
remote refid st t when poll reach delay offset jitter
==============================================================================
xGPS_ONCORE(0) .GPS. 0 l 5 16 377 0.000 -15999. 0.002
+time-C.timefreq .ACTS. 1 u 19 64 377 37.887 -16011. 0.122
*ntp-nasa.arc.na .GPS. 1 u 24 64 377 19.760 -16000. 0.027
Finally after 30 minutes, a lock and convergence, but still big offsets:
remote refid st t when poll reach delay offset jitter
==============================================================================
oGPS_ONCORE(0) .GPS. 0 l 4 16 377 0.000 172.425 34.702
+time-C.timefreq .ACTS. 1 u 29 64 77 37.579 151.544 104.339
*ntp-nasa.arc.na .GPS. 1 u 22 64 77 19.779 165.811 106.581
Is there anything I can do to decrease the convergence time?
Little or nothing! NTPD can, and sometimes does, take ten hours to
reach "steady state". It needs about thirty minutes to find a
reasonable facsimile of the correct time. For the next nine hours and
thirty minutes, it will refine that value until it's as good as it's
going to get.
If you maintain a constant temperature in the room in which you keep
your computers, NTPD will maintain an accurate and stable clock as long
as you maintain that stable temperature.
If you can't maintain that steady state you need to either fix things
until you can or lower your expectations.
There is another "product" That will synchronize quickly. I don't
recall its name. Supposedly there is a price in accuracy and stability
for that quick start. Consult the Control Systems Theory people about
the NTP algorithms and how they differ from algorithms giving fast
convergence.
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