Hello timelords,
I have a Garmin GPS25-LVC connected to the serial port of a Via EPIA M
server, running ntpd 4.2.0a+stable and Linux 2.6.15.7 patched
with `PPSkit-light-alpha-3328m-2.6.15.1.diff'.
Whilst this combination is functioning, I am a little concerned about
the output of ntptime:
ntp_gettime() returns code 0 (OK)
time c82c2865.688c0cc4 Sat, Jun 3 2006 16:25:25.408, (.408387508),
maximum error 1101 us, estimated error 7 us, TAI offset -1208107020
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset -347.839 us, frequency 0.117 ppm, interval 8 s,
maximum error 1101 us, estimated error 7 us,
status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
time constant 4, precision 0.001 us, tolerance 496 ppm,
pps frequency 0.117 ppm, stability 0.536 ppm, jitter 2.559 us,
intervals 63043, jitter exceeded 3769, stability exceeded 576, errors 35639.
Over 50% of the calibration intervals are resulting in errors, which is
presumably why I am seeing the following in my logs, often over twice a
minute:
Jun 3 16:15:07 evolution ntpd[25365]: kernel time sync enabled 2107
Jun 3 16:15:23 evolution ntpd[25365]: kernel time sync disabled 2907
Jun 3 16:15:42 evolution ntpd[25365]: kernel time sync enabled 2107
Jun 3 16:17:00 evolution ntpd[25365]: kernel time sync disabled 2307
Jun 3 16:17:18 evolution ntpd[25365]: kernel time sync enabled 2107
Jun 3 16:18:43 evolution ntpd[25365]: kernel time sync disabled 2907
Jun 3 16:19:01 evolution ntpd[25365]: kernel time sync enabled 2107
Status 2907 is STA_PPSERROR, and 2307 is STA_PPSJITTER according to
timex.h, so this correlates with the output of ntptime above.
In general performance seems good, as shown by the output of ntpq:
remote refid st t when poll reach delay offset jitter
==============================================================================
*GPS_NMEA(0) .GPS. 0 l 10 16 377 0.000 0.003 0.001
+ntp0.zen.co.uk 195.66.241.3 2 u 37 64 377 16.534 1.844 0.386
+veracity.mcc.ac 193.62.22.98 2 u 5 64 377 16.541 1.290 2.207
+ntp0.ja.net .MSF. 1 u 35 64 377 21.979 1.469 0.168
+ntp1.linx.net .1PPS. 1 u 30 64 377 28.651 0.943 40.229
+tt01.ripe.net .GPS. 1 u 6 64 377 32.381 1.350 0.903
However, jitter, noise and offset will occasionally shoot up to
stupidly high levels (I have generated some short term graphs to
demonstrate this [0]).
Is this likely to be a hardware or wiring issue? I was previously using
a version of David J. Schwartz's SHM PPS driver, and it appeared to work fine.
Any ideas would be much appreciated.
[0] http://excus.es/ntpd/
--Adam
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