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

David Lord snews at lordynet.org
Mon Sep 19 08:21:44 UTC 2011


Miguel Gonçalves wrote:
> 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
> 

NetBSD-5, ntpd 4.2.6p3

My time sync has blipped twice each evening at times when
system load is high during log creation/rotation. Mostly
I don't notice. Currently I'm using a Sure-Electronics
but my Garmin 18x-LVC was the same. Blips are from < 15u
up to over 40u.

peerstats.20110918
        ident     mean    rms    max delay  dist  disp
127.127.20.2  -64.698 15.422 60.828 0.000 2.525 1.742
127.127.22.2    0.000  0.000  0.048 0.000 0.928 0.920


David


> Can anyone help??
> 
> Thanks!
> 
> Cheers,
> Miguel




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