[ntp:questions] Re: Configuring dual refclock/PPS sources
John R. Ackermann N8UR
jra at febo.com
Fri Jan 16 14:11:55 UTC 2004
I went ahead and tried to configure ntpd to use a pair of Z3801A
GPS-disciplined oscillators. I think I can verify that, at least under
FreeBSD 4.9 with a PPS-enabled kernel, just duplicating the server lines
doesn't work.
Here's the relevant part of ntp.conf:
enable pps
pps /dev/pps0 assert hardpps
server 127.127.26.0 prefer ttl 1
fudge 127.127.26.0 time1 -0.966
fudge 127.127.26.0 refid GPS0
server 127.127.22.0
fudge 127.127.22.0 refid PPS0
pps /dev/pps1 assert hardpps
server 127.127.26.1 prefer ttl 1
fudge 127.127.26.1 time1 -0.966
fudge 127.127.26.1 refid GPS1
server 127.127.22.1
fudge 127.127.22.1 refid PPS1
The single-clock version of this worked fine, but this attempt clearly
doesn't do the job (note particularly the horrible ntptime statistics --
with a single PPS source, the stability is more like 0.02ppm):
$ ntpq -p
remote refid st t when poll reach delay offset
jitter
===========================================================================
===
+GPS_HP(0) .GPS0. 0 l 59 64 377 0.000 -27.719
6.811
PPS(0) PPS(0) 16 l 247 64 110 0.000 -20.462
0.086
+GPS_HP(1) .GPS1. 0 l 43 64 377 0.000 -29.444
7.138
oPPS(1) .PPS1. 0 l 17 64 377 0.000 -20.465
0.002
-time-C.timefreq .ACTS. 1 u 44 64 377 102.044 -20.903
0.134
xntp2.usno.navy. .USNO. 1 u 3 64 377 191.221 -13.602
4.940
xtick.usno.navy. .USNO. 1 u 13 64 377 198.978 -11.235
3.321
$ ntptime
ntp_gettime() returns code 0 (OK)
time c3b26efc.0597f628 Fri, Jan 16 2004 9:09:00.021, (.021850349),
maximum error 12931 us, estimated error 1 us, TAI offset 0
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset -20465.123 us, frequency 412.662 ppm, interval 64 s,
maximum error 12931 us, estimated error 1 us,
status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
time constant 6, precision 0.001 us, tolerance 496 ppm,
pps frequency 412.662 ppm, stability 31.779 ppm, jitter 3.815 us,
intervals 712, jitter exceeded 577, stability exceeded 3, errors 688.
So, do I gather that FreeBSD can't support multiple PPS sources? Or are
there configuration changes that will fix this?
John
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