[time-nuts] Recommendations for NTP server
John Ackermann N8UR
jra at febo.com
Sun Apr 23 22:12:28 UTC 2006
Geoff Powell said the following on 04/23/2006 05:42 PM:
> Is PPS kernel discipline compiled into the default FreeBSD kernel?
No, but it's a pretty easy thing to turn on -- you add a line to the
config file and tell it to go. Pretty straightforward, *once* you find
the instructions.
>
>
>>I am not running 2.6.15 because it has some problems with the linux-gpib
>>drivers that I depend on for data logging, but instead using a shared
>>memory driver called "shm_linux_clock" that runs as a separate program
>>and monitors a serial port for PPS and passes that through to NTP. It
>>works very well and holds within 10s of microseconds, most of the time.
>
>
> Does this require a kernel recompile, is it a module, or does it run in
> userland?
It runs in userland. You need to make sure that your NTP has the shared
memory refclock compiled in.
> Yes, I noticed that all the machines vary more-or-less together, which
> suggests a common-mode effect - is databox playing up?
Yes, yesterday databox suffered an unplanned reboot, which exposed some
configuration problems. It took quite a while to get everything playing
properly, and then NTP takes a while to settle down.
I have a Soekris 4501 on order (do you detect a theme?) and plan to lock
its oscillator to the house timebase, and then switch the monitoring
task over to that machine and away from databox. For now, I get a sense
of how databox is performing by looking at the common mode effect on the
other servers.
>
> I know that radio clocks (I'd be using MSF Rugby, or DCF Mainflingen)
> are poor in comparison, and probably worse than your WWVB results,
> because the receivers I'd be using would have a lot less intelligence
> than yours.
>
I don't know -- the Spectracom receiver is pretty ancient technology,
and I suspect that Jonathan Buzzard's code running on a modern machine
might give it a good run for its money. The biggest problem with the
Spectracom is that when it loses lock once every 10 days or so, there is
a sudden multi-millisecond offset that takes a couple of days to fully
recover from.
John
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