On 25/11/2012 21:37, Dave Hart wrote:
[]
Jitter is a measure of the variability of the phase offset across up
to eight entries in the clock filter register of the selected peer,
the "best" sample of which ends up as the third column of loopstats.
For a LAN peer best is lowest delay. For PPS, it's the most recent,
as the delays are all zero and older entries accumulate more error
budget. I expect the Windows PC to have a somewhat higher jitter than
similar hardware running FreeBSD or Linux, but the pattern of exactly
zero jitter recorded by your ARM-powered Pi doesn't look credible to
me. It's happening right off the bat for the LAN source at startup,
and then shortly after switching to PPS.
I bet you don't see any exactly zero jitter in loopstats on your
FreeBSD PPS server. I wonder if x86/x64 Linux ntp-dev users see
anything similar?
I'd appreciate others taking a look at their loopstats on Linux
systems and especially non-x86 Linux to see if 0.000000000 shows up in
the jitter (fifth column). I think we need more information to
understand the problem.
Cheers,
Dave Hart
Dave,
Many thanks for your reply. I have just enabled loopstats logging on
the FreeBSD server and, just as you expected, the values are not zero
(averaging at just over 2 microseconds).
I would expect the ~700 MHz ARM systems to be a little worse than the
FreeBSD box, which is an Intel single-core, hyperhtreaded 1.66 GHz Atom.
--
Cheers,
David
Web: http://www.satsignal.eu
_______________________________________________
questions mailing list
questions@lists.ntp.org
http://lists.ntp.org/listinfo/questions
