On 16/12/2013 11:16, Adrian P wrote:
Hi,
In an old IBM thinkpad T22 laptop that runs FreeBSD 9.2, I have
configured a NTP server that gets the PPS signal from a Garmin GPS 18
LVC, as described here:
http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
The /etc/ntp.conf contains the following generic NMEA GPS receiver
driver configuration:
server 127.127.20.0 mode 1 minpoll 4 maxpoll 4 prefer
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 refid PPS
I let it run for a few days, however I still have every now and then
huge peaks (between -50 and +30 us) of the clock offset as seen in the
following graph: http://goo.gl/JpSyeO
So I am wondering: why those repeating huge clock offsets? They
allays starts with a negative peak, followed immediately by a positive
one. Is this because of the faulty laptop internal clock, that drifts
away with 30-40 us every now and then? Any thoughts?
Many thanks,
Adrian
In addition to what the others have suggested, does you GPS 18 LVC have
a good view of the sky? It's nothing like as sensitive as the newer 18x
LVC (note the "x").
If it helps to compare, the data from my own Intel Atom FreeBSD 8.2
system is here - PC Pixie:
http://www.satsignal.eu/mrtg/performance_ntp.php
As it's plotted with MRTG it's only sampled at 5 minute intervals, and
the droop in the yearly graph is an artefact of MRTG's summarising, it's
not real. My GPS 18 LVC is mounter on the roof, sloping towards the
west at an angle of about 22 degrees and slightly sheided by adjacent
houses, so not a 360 degree view, but not inside either.
--
Cheers,
David
Web: http://www.satsignal.eu
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