[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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