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

unruh unruh at wormhole.physics.ubc.ca
Mon Sep 19 17:38:39 UTC 2011


On 2011-09-19, David Lord <snews at lordynet.org> wrote:
> Miguel Gon?alves 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.

Clearly a problem with interrupt processing then. the interrupt is being
delayed (disk activity? ) by many us by something. 

>
> 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




More information about the questions mailing list