sleek daelite wrote:
Could anyone help me with Garmin GPS 18lvc device that comes with PPS
output. I've been trying to configure the device to achieve about 1ms
accuracy. The specification of this device states it could achieve about
1ns accuracy. Im quite puzzled as to why i can't achieve such accuracy.
1ns is just not going to happen on PC hardware.
Whether you can get sub-ms speeds depends a lot on the hardware - a fast
processor helps. System load is critical (best to dedicate a machine to
ntp serviing really).
With the shm driver which requires a daemon, you're at the mercy of the
scheduler that it even runs that daemon at the right moments.. you're
likely to get better results with the kernel PPS driver because it
doesn't have that issue. If you can't do that try putting gpsd at
realtime priority.
Also note that the garmin is not a particularly sensitive GPS device (in
fact it's not sensitive *at all* - picking up enough satellites to lock
less than 25% of the day here with a clear view of the sky) so you might
be reading it at the wrong moment. Unfortunately unlike 'proper' GPS
clocks the garmin can't be configured to lock onto a single satellite
(since it's not moving it doesn't need to calculate its position).
My content of ntp.conf is:
-------------------------------------------------------------
server 127.127.28.0 <http://127.127.28.0> minpoll 4 maxpoll 4
fudge 127.127.28.0 <http://127.127.28.0> time1 0.320 refid GPS
server 127.127.28.1 <http://127.127.28.1> minpoll 4 maxpoll 4 prefer
fudge 127.127.28.1 <http://127.127.28.1> refid GPS1
Why do you have two??? Is one a reference clock (MSF?)?
Tony
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