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

David Lord snews at lordynet.org
Mon Sep 19 18:01:45 UTC 2011


unruh wrote:
> 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. 


I didn't see it as a problem, but whatever, I'll continue
to live with it.


David




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