[ntp:questions] NMEA refclock - PPS not working

R Jenkins not at pub.lished
Sun May 14 21:48:58 UTC 2006


Hi again..
My previous problem with ntpq timing out was solved by using the latest dev 
release of the NTP source, it appears to be a bug in the (old) version used 
by Redhat / Centos 4.

I can now monitor ntpd, but it's still not locking to the PPS input.
The relevent bit of ntp.conf is:

# NMEA Clock using Garmin GPS
server 127.127.20.0 mode 1 version 4 prefer
fudge 127.127.20.0 refid GPS flag3 1 time1 0.042 stratum 1
(plus three other servers).

Kernel 2.6.16.9 with ppskit-lite patch.

These are the results after about half an hour:
ntpq -c peers
     remote           refid      st t when poll reach   delay   offset 
jitter
==============================================================================
xGPS_NMEA(0)     .GPS.            1 l   39   64  377    0.000  -263.67 
145.858
+gate.jrw.intra  130.159.196.118  3 u    -   16  377    0.212  252.072 
19.115
*Time2.Stupi.SE  .PPS.            1 u   46   64  377   52.478  191.170 
85.622
+arg.cmm.ki.si   131.188.3.223    2 u   45   64  377   61.012   49.949 
105.216

ntptime
ntp_gettime() returns code 0 (OK)
  time c812205b.41762000  Sun, May 14 2006 22:32:11.255, (.255709),
  maximum error 719516 us, estimated error 44711 us
ntp_adjtime() returns code 0 (OK)
  modes 0x0 (),
  offset 19886.000 us, frequency -390.653 ppm, interval 4 s,
  maximum error 719516 us, estimated error 44711 us,
  status 0x1 (PLL),
  time constant 2, precision 1.000 us, tolerance 496 ppm,
  pps frequency 0.000 ppm, stability 0.000 ppm, jitter 0.000 us,
  intervals 0, jitter exceeded 0, stability exceeded 0, errors 0.

This was after initially running ntpdate against the stratum 1 server & 
deleting the drift file.

The ntptime 'frequency 390.653 ppm' entry is slowly oscillating. It's been 
to both extremes +/- 495.9ppm.
Eventually the offset drifts to the point where it does a jump or step.

The jitter on the first server line seems odd to me, it's a local machine on 
a gigabit link with next to no other network traffic at the moment.
I'm beginning to think there is either something wierd with the board  or 
BIOS - it's a Gigabyte K8N Ultra-9 with an nforce4 chipset & Athlon 64 3200.

Alternately, is there another PPS mode that runs without the kernel patch? 
That should still be better than using internet servers only.

Robert Jenkins.





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