[ntp:questions] Configuring dual refclock/PPS sources

John R. Ackermann N8UR jra at febo.com
Thu Jan 15 15:11:58 UTC 2004

Hi --

I have a pair of HP Z3801A GPS-disciplined oscillators that I've modified 
to act (for ntpd's purposes) more-or-less like an HP 53503A "smart clock." 
I have one of the units running pretty well using the following ntp.conf 

enable pps
pps /dev/pps0 assert hardpps

server prefer ttl 1
fudge time1 -0.966

fudge refid GPS

I'm running ntpd version 4.1.1rc3 (from the FreeBSD 4.9 ports kit) so I 
needed to use the "pps..." line to get the kernel discipline going.  Also, 
without the "ttl 1" option, the hpgps driver never kicked in; I have no 
idea why.

My question is how to configure for the second unit on the same machine, 
which I have no reason to believe is any better or worse in timekeeping 
performance than the first.  Do I just duplicate these lines, changing the 
address to unit 1?

In particular, the docs discourage having multiple servers tagged with the 
"prefer" keyword, but how do I ensure that if the "prefer" unit fails, the 
kernel discipline and PPS driver keep working from the remaining unit?



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