[ntp:questions] Garmin 18 LVC high offset and jitter

Miguel Gonçalves mail at miguelgoncalves.com
Sun Sep 18 19:48:51 UTC 2011


Hi all!

I am having a problem with a Dell server that has a Garmin 18 LVC attached.

It's a FreeBSD 7.4 machine with the Garmin 18 LVC connected to a serial port
(PPS on DCD pin). The kernel has been compiled with the line "OPTIONS
PPS_SYNC". NTP is 4.2.4p5.

Here's the ntp.conf file:

server 127.127.20.0 mode 2 iburst prefer
fudge 127.127.20.0 flag3 1

server ntp-p1.obspm.fr iburst
server ptbtime1.ptb.de iburst
server ntp.inrim.it iburst
server ntp1.oma.be iburst

server canon.inria.fr iburst
server time.fu-berlin.de iburst
server chronos.csr.net iburst
server ntp1.nl.uu.net iburst

statsdir /var/log/ntp/
filegen clockstats file clockstats type day enable
filegen peerstats file peerstats type day enable
filegen loopstats file loopstats type day enable
statistics clockstats peerstats loopstats

logfile /var/log/ntp/messages

restrict default kod nomodify notrap nopeer
restrict 127.0.0.1

I've disabled ACPI in /boot/loader.conf (hint.acpi.0.disabled=1) but did not
disable serial FIFO.

I am getting very high offsets and jitter for this reference clock:

     remote           refid      st t when poll reach   delay   offset
 jitter
==============================================================================
*GPS_NMEA(0)     .GPS.            0 l   40   64  377    0.000   -0.031
0.043
+ntp-p1.obspm.fr .TS-3.           1 u   50   64  377   54.154    1.611
1.843
-ptbtime1.ptb.de .DCFa.           1 u  119   64  376   70.069   -2.174
1.283
-ntp.ien.it      .CTD.            1 u   35   64  377   65.682    2.037
6.667
-ntp1.oma.be     .PPS.            1 u   26   64  377   61.911    2.280
3.673
+canon.inria.fr  .GPSi.           1 u   30   64  377   54.626    1.442
1.700
-time.fu-berlin. .PPS.            1 u   32   64  377   73.342   -0.292
3.136
-chronos.csr.net .GPS.            1 u   32   64  377   85.049   -3.656
5.096
-ntp1.nl.uu.net  .PPS.            1 u    2   64  377   67.085    3.435
3.888

tick# ntpdc -c kerninfo
pll offset:           -7.886e-06 s
pll frequency:        -6.729 ppm
maximum error:        0.030005 s
estimated error:      6e-06 s
status:               2107  pll ppsfreq ppstime ppssignal nano
pll time constant:    6
precision:            1e-09 s
frequency tolerance:  496 ppm
pps frequency:        -6.729 ppm
pps stability:        0.312 ppm
pps jitter:           4.03e-07 s
calibration interval: 256 s
calibration cycles:   152
jitter exceeded:      1029
stability exceeded:   0
calibration errors:   3

It seems the internal clock of the machine is going nuts (small snippet of
loopstats file):

55822 70649.300 0.000037529 -6.306 0.000000816 0.139388 6
55822 70714.307 0.000004089 -6.175 0.000001464 0.138376 6
55822 70779.307 -0.000029839 -6.175 0.000013699 0.129439 6
55822 70845.306 -0.000058655 -6.175 0.000000562 0.121079 6
55822 70909.305 -0.000078382 -6.175 0.000000570 0.113259 6
55822 70972.305 -0.000061801 -6.729 0.000001320 0.222533 6
55822 71035.304 -0.000041884 -6.729 0.000000778 0.208161 6
55822 71100.304 -0.000023847 -6.729 0.000000629 0.194717 6
55822 71166.303 -0.000003148 -6.595 0.000001515 0.188165 6
55822 71232.302 0.000006531 -6.595 0.000004666 0.176012 6

Can anyone help??

Thanks!

Cheers,
Miguel



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