On 11/29/2011 9:21 PM, unruh wrote:
On 2011-11-29, Richard B. Gilbert<rgilber...@comcast.net> wrote:
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
Possibly chrony. Except that the "price" of faster convergence is vastly
improved accuracy and just as stable as NTPD.
But it only runs on Linux or bsd, not windows.
(If time spans, rather than time is most important to you, then chrony
might be slightly worse than ntpd, because of the algorithm used to
correct the clock-- a fairly rapid slew to correct the offset, and a
frequency change to correct the drift. )
Note that if you get rid of ntpd's drift file, and use the burst option,
you can get faster convergence from ntpd apparently.
I think the effect of getting rid of the drift file depends on the value
stored in the file! If the value is reasonably close to correct, I
think it's helpful. If you are restarting because you have been without
power for the last three hours, the drift file is almost certainly useless!
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