A C wrote:
Is there a way to configure ntpd to ignore a particular clock unless
there is no other choice? What I'm thinking is to ignore the GPS
receiver NMEA data and use only the PPS plus Internet servers for most
of the synchronization. But if the Internet servers go down, accept the
GPS NMEA data for seconds numbering and let the tick be controlled by PPS.
Doesn't ntp do that already?
If you have nmea + pps the pps will be used for sync.
If your gps + pps is down your internet servers will be used for sync.
Wed Nov 2 00:00:00 GMT 2011
remote refid st t when poll reach delay offset
jitter
==============================================================================
*GPS_NMEA(2) .GPSb. 0 l 29 64 377 0.000 -52.888
11.213
oPPS(2) .PPSb. 0 l 28 64 377 0.000 -0.001
0.004
p4x2400b.home.l 192.168.59.61 2 u 6 64 377 1.157 -3.917
0.908
p4x2400c.home.l 192.168.59.61 2 u 19 64 377 0.729 2.298
0.619
pd6000e1.home.l 192.168.59.61 2 u 11 64 377 0.544 1.767
0.551
pd6000e2.home.l 192.168.59.61 2 u 54 64 377 0.494 0.983
0.535
+ntp1.lordynet.o 81.187.61.74 2 u 7 128 377 0.854 2.089
0.520
+ntp0.lordynet.o .MSFa. 1 u 1 128 377 0.934 1.548
0.572
offset: -0.000001 s
frequency: -35.833 ppm
poll adjust: 30
watchdog timer: 28 s
ntp_gettime() returns code 0 (OK)
time d25b0680.8615a8ac Wed, Nov 2 2011 0:00:00.523, (.523768144),
maximum error 14934 us, estimated error 4 us, TAI offset 34
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset 1.094 us, frequency -35.833 ppm, interval 256 s,
maximum error 14934 us, estimated error 4 us,
status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
time constant 6, precision 0.001 us, tolerance 496 ppm,
pps frequency -35.833 ppm, stability 0.020 ppm, jitter 2.688 us,
intervals 17356, jitter exceeded 15439, stability exceeded 0, errors 19.
David
I guess I'm asking for something opposite to the "prefer" flag, a "not
unless you have to" flag. The GPS does get selected among the various
clock sources but it's the worst of the bunch with respect to jitter and
offset. Those two wander all over while the rest of the Internet
servers and the PPS are stable. It is almost never rejected as an
outlier or false ticker even if it's way out of line with the other
sources.
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