On 8/27/2014 5:48 AM, [email protected] wrote:
I not sure, how should I write the ntp.conf file to achieve the maximum
accuracy using pps.
i don't know if the ntpd use the pps or not in my case!
Sometimes it is recognized as a "falseticker" (x) and sometimes it is OK(o) !!!
Try adding "tos mindist 0.02" to your config.
NMEA tends to wander around - the default mindist of 0.001 can result in
what you see. You might try setting it even higher, and work your way
down to a reliable minimum.
From the docs:
mindist mindistance
Specify the minimum distance used by the selection and anticlockhop
algorithm. Larger values increase the tolerance for outliers; smaller
values increase the selectivity. The default is .001 s. In some cases,
such as reference clocks with high jitter and a PPS signal, it is useful
to increase the value to insure the intersection interval is always
nonempty.
I tested different ntp.conf and here are some results (ntp.conf and ntpq-p):
#TEST:1
----- ntp.conf-------
server 127.127.22.1 minpoll 4 #PPS
server 127.127.20.1 prefer minpoll 4 mode 16 #GPS
fudge 127.127.20.1 flag1 1 flag3 1
-----
GPS on COM port (PPS connected to DCD pin)
remote refid st t when poll reach delay offset jitter
==============================================================================
xPPS(1) .PPS. 0 l 3 16 377 0.000 30.681 29.011
oGPS_NMEA(1) .GPS. 0 l 2 16 377 0.000 29.964 29.404
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