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On 8/9/2016 2:02 AM, Jon Brase wrote:
Just a quick question: Is it typical for the data that
GPSD hands to NTP through the shared memory driver to arrive with
a ~500 ms offset from top-of-second as shown by PPS (where NTP is
pulling the PPS data directly) or by external timeservers? The
hardware is a Raspberry Pi running Raspbian Jessie with an
Adafruit GPS breakout, with the following server configuration in
/etc/ntp.conf:
I'm using Jessie with instructions here:
https://frillip.com/raspberry-pi-stratum-1-ntp-server/
and a Garmin GPS16X-HVS. My clock line is:
server 127.127.20.0 mode 49 minpoll 4 maxpoll 4 iburst true prefer
server 127.127.20.0 time2 0.45 flag1 1 refid GPS
So, yes I would say it's normal. Without the offset, I wouldn't get
a PPS lock because the time differential was too big.
------------------------------------------------------------------------------
#coarse time from GPSD
server 127.127.28.0 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.0 time1 0.47 refid GPS
#PPS ref-clock for top-of-second
server 127.127.22.0 minpoll 4 maxpoll 4
fudge 172.127.22.0 refid PPS
# pool.ntp.org maps to about 1000 low-stratum NTP servers. Your
server will
# pick a different set every time it starts up. Please consider
joining the
# pool: <http://www.pool.ntp.org/join.html>
server 0.debian.pool.ntp.org iburst
server 1.debian.pool.ntp.org iburst
server 2.debian.pool.ntp.org iburst
server 3.debian.pool.ntp.org iburst
------------------------------------------------------------------------------
I found that I needed a time1 offset in the .45 to .5 range
(currently .47, as shown above), to get the coarse GPS time to
line up with the PPS / external timeserver time. Is this typical?
I'm just wanting to make sure that it doesn't indicate some gross
misconfiguration, as half a second seems like a rather large
fudge. If everybody here thinks everything is fine, though, I
think I will be ready to take leave of this list, as this is the
last outstanding GPSD-specific issue I have with my GPS timeserver
project.
On that note, what's the most appropriate forum for discussing
general issues with setting up a GPS timeserver (for example, some
of the output I'm getting from ntpq doesn't match what the
references I used for setup lead me to expect, and I suspect
misconfiguration or other problems with ntpd)?
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