[ntp:questions] Everything works! -- but am I doing more than I need to?
John Ackermann N8UR
jra at febo.com
Wed Nov 26 01:30:46 UTC 2003
Thanks for several helpful responses to my question yesterday re the Oncore
driver on a FreeBSD system. I'm now up and running, but am still somewhat
baffled by the various bits of documentation and the relationship between
the Oncore driver, the PPS driver, and the kernel PPS discipline. I'm
running ntpd version 4.1.1c-rc3 from the FreeBSD ports collection.
Here's the operative part of my /etc/ntp.conf file:
pps /dev/oncore.pps.0 assert hardpps
server 127.127.30.0 prefer
fudge 127.127.30.0 flag3 1
And here's what ntpq -p shows:
+GPS_ONCORE(0) .GPS. 0 l 5 16 377 0.000 0.000
oPPS(0) .PPS. 0 l 13 64 377 0.000 0.003 0.003
My question is how many of those lines in /etc/ntp.conf are needed.
I've seen references that seem to indicate that the server 127.127.30.0
prefer" line is all you need, but without setting flag3 it doesn't appear
that the kernel PPS discipline is started.
I've seen references that say that the Oncore driver "handles all the PPS
stuff" but without the "server 127.127.22.0" line, I never got the PPS
driver to appear in the ntpq -p output.
I've seen references that indicate (I think) that you don't want to use the
kernel PPS discipline because ntpd does a better job. So, I'm not sure if
I *want* the PPS driver to be there...
So, what to do? What setup will yield optimum timekeeping performance for
an Oncore hooked to a FreeBSD ntp box (I'm using FreeBSD on this dedicated
system because of the numerous comments on the list over time that Linux
PPS is a box of horrors; I can take a hint :-) ).
For what it's worth, I've also attached the results of ntptime at the end
of this message. While we're at it, do the number of "jitter exceeded" and
"errors" shown seem reasonable? The system has been running for about 8
ntp_gettime() returns code 0 (OK)
time c36e7ff3.fecd4a40 Tue, Nov 25 2003 20:27:15.995, (.995320576),
maximum error 33873 us, estimated error 2 us, TAI offset 0
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset -2.973 us, frequency 95.808 ppm, interval 256 s,
maximum error 33873 us, estimated error 2 us,
status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
time constant 6, precision 0.001 us, tolerance 496 ppm,
pps frequency 95.808 ppm, stability 0.015 ppm, jitter 1.072 us,
intervals 169, jitter exceeded 68, stability exceeded 0, errors 7.
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