[time-nuts] NTP, PPS and < 10 us offsets

Miguel Barbosa Gonçalves m at mbg.pt
Thu May 16 13:56:06 UTC 2013


On 16 May 2013 11:12, Miguel Barbosa Gonçalves <m at mbg.pt> wrote:

> On 16 May 2013 04:14, Chris Albertson <albertson.chris at gmail.com> wrote:
>
>> On Wed, May 15, 2013 at 12:43 PM, Miguel Barbosa Gonçalves <m at mbg.pt>
>> wrote:
>>
>>
>> >
>> > I've reconfigured the antenna to output only NMEA sentences (and I also
>> use
>> > the PPS) and NTP works fine but suddenly without any explanation the NTP
>> > process stops receiving information from the receiver. I really don't
>> > understand what's happening here as the receiver is on the roof and sees
>> > plenty of satellites:
>>
>>
>> Even if there were zero satellites the GPS receiver should report zero,
>> not
>> just stop and die.
>>
>> Are you certain that both PPS and NMEA data both stop?  If just one of
>> them, then I'd suspect a bad connection, a loose cable or something.   If
>> both then I'd suspect the receiver or its power supply or the rs422 to
>> rs232 converter or its power supply.  Power is the easiest thing to check.
>>
>
>
> Hi Chris!
>
> Thanks for your help. The strange thing is that is works and suddenly it
> stops.
>
> I changed the offset of the NMEA data in NTP and increased the mindist to
> 0.250.
> It is running since 21:12 UTC without problems. I will let it run for 48
> hours before
> entering production.
>

I was monitoring this server closely and here's what happened


56428 27303.926 0.000006800 158.256 0.000000396 0.005945 4
56428 27319.926 0.000006325 158.256 0.000000552 0.005561 4
56428 27335.926 0.000005382 158.256 0.000000673 0.005202 4
56428 27351.926 0.000005656 158.256 0.000000786 0.004866 4
56428 27367.926 0.000004605 158.256 0.000000498 0.004552 4
56428 27383.926 0.000004386 158.256 0.000000644 0.004258 4
56428 27399.926 0.000003148 158.256 0.000000315 0.003983 4
56428 27415.926 0.000002788 158.256 0.000000485 0.003725 4
56428 27431.926 0.000002173 158.256 0.000000569 0.003485 4
56428 27447.926 0.000001682 158.256 0.000000543 0.003260 4

56428 27463.926 0.000000393 158.256 0.000001338 0.003049 4
56428 27479.926 -0.000695347 258.256 0.000174991 35.355339 4

56428 27495.925 -0.002219770 258.256 0.000186611 33.071891 4
56428 27511.926 -0.003650615 258.256 0.000175434 30.935922 4
56428 27527.926 -0.004993533 258.256 0.000164605 28.937905 4
56428 27543.925 -0.006255032 258.256 0.000154519 27.068932 4
56428 27559.925 -0.007438843 258.256 0.000145242 25.320667 4
56428 27575.925 -0.008550950 258.256 0.000136390 23.685315 4
56428 27591.926 -0.009594694 258.256 0.000128180 22.155584 4
56428 27607.925 -0.010574400 258.256 0.000120117 20.724651 4
56428 27623.925 -0.011495082 258.256 0.000112889 19.386136 4
56428 27639.925 -0.012358729 258.256 0.000105844 18.134069 4


56428 27303.926 127.127.20.0
$GPGGA,073503.0,4055.226,N,00829.616,W,1,10,0.91,00257,M,051,M,,*41
56428 27319.926 127.127.20.0
$GPGGA,073519.0,4055.228,N,00829.619,W,1,08,1.15,00269,M,051,M,,*42
56428 27335.926 127.127.20.0
$GPGGA,073535.0,4055.228,N,00829.619,W,1,08,1.15,00270,M,051,M,,*44
56428 27351.926 127.127.20.0
$GPGGA,073551.0,4055.228,N,00829.619,W,1,08,1.15,00269,M,051,M,,*4E
56428 27367.926 127.127.20.0
$GPGGA,073607.0,4055.228,N,00829.618,W,1,08,1.15,00270,M,051,M,,*47
56428 27383.926 127.127.20.0
$GPGGA,073623.0,4055.228,N,00829.620,W,1,09,1.04,00275,M,051,M,,*4E
56428 27399.926 127.127.20.0
$GPGGA,073639.0,4055.228,N,00829.620,W,1,09,1.04,00277,M,051,M,,*47
56428 27415.926 127.127.20.0
$GPGGA,073655.0,4055.227,N,00829.620,W,1,09,1.04,00275,M,051,M,,*40
56428 27431.926 127.127.20.0
$GPGGA,073711.0,4055.228,N,00829.617,W,1,09,1.04,00262,M,051,M,,*4C
56428 27447.926 127.127.20.0
$GPGGA,073727.0,4055.228,N,00829.617,W,1,09,1.04,00262,M,051,M,,*49

56428 27463.926 127.127.20.0
$GPGGA,073743.0,4055.229,N,00829.618,W,1,09,1.04,00268,M,051,M,,*4F
56428 27479.926 127.127.20.0
$GPGGA,073759.0,4055.228,N,00829.619,W,1,09,1.05,00273,M,051,M,,*4F

56428 27495.925 127.127.20.0
$GPGGA,073815.0,4055.228,N,00829.619,W,1,10,0.91,00268,M,051,M,,*46
56428 27511.926 127.127.20.0
$GPGGA,073831.0,4055.228,N,00829.617,W,1,10,0.91,00262,M,051,M,,*44
56428 27527.926 127.127.20.0
$GPGGA,073847.0,4055.229,N,00829.617,W,1,10,0.91,00263,M,051,M,,*45
56428 27543.925 127.127.20.0
$GPGGA,073903.0,4055.229,N,00829.617,W,1,10,0.92,00264,M,051,M,,*40
56428 27559.925 127.127.20.0
$GPGGA,073919.0,4055.229,N,00829.617,W,1,10,0.92,00265,M,051,M,,*4A
56428 27575.926 127.127.20.0
$GPGGA,073935.0,4055.228,N,00829.617,W,1,10,0.92,00265,M,051,M,,*45
56428 27591.926 127.127.20.0
$GPGGA,073951.0,4055.229,N,00829.617,W,1,10,0.92,00264,M,051,M,,*47
56428 27607.926 127.127.20.0
$GPGGA,074007.0,4055.229,N,00829.618,W,1,10,0.92,00266,M,051,M,,*47
56428 27623.925 127.127.20.0
$GPGGA,074023.0,4055.229,N,00829.618,W,1,10,0.92,00270,M,051,M,,*46
56428 27639.925 127.127.20.0
$GPGGA,074039.0,4055.229,N,00829.618,W,1,10,0.92,00272,M,051,M,,*4F


Nothing out of the ordinary happened physically around the server at
27479.926 for this huge jump in frequency... I don't understand this...

It is running fine and suddenly a huge jump in frequency.

I am running NTP 4.2.6p5 and here's my config file

server 127.127.20.0 prefer mode 18 minpoll 4 maxpoll 4
fudge 127.127.20.0 time2 0.215 flag1 1 flag3 1

server ntp3 iburst burst minpoll 4 maxpoll 4
server ntp4 iburst burst minpoll 4 maxpoll 4

tos mindist 0.250

statistics loopstats peerstats clockstats
statsdir /var/log/ntp/
filegen clockstats file clock.ntp2 type day link enable
filegen peerstats file peers.ntp2 type day link enable
filegen loopstats file loop.ntp2 type day link enable

restrict 127.0.0.1
restrict 10.0.2.3 nomodify notrap nopeer
restrict 10.0.2.4 nomodify notrap nopeer
restrict default nomodify notrap nopeer noquery noserve


How can I debug this problem?

Any help will be appreciated!

Cheers,
Miguel



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