[ntp:questions] Preffered OS for a GPS based stratum 1

Unruh unruh-spam at physics.ubc.ca
Fri Oct 31 22:42:59 UTC 2008

oberman at es.net (Kevin Oberman) writes:

>> From: Terje Mathisen <terje.mathisen at hda.hydro.com>
>> Date: Fri, 31 Oct 2008 08:59:06 +0100
>> Sender: questions-bounces+oberman=es.net at lists.ntp.org
>> Spiffed wrote:
>> > I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS 
>> > stretching converter box. WinOncore shows a 'Time Solution one sigma' of 
>> > 38ns, so it seems to be an acceptable ref clock for my purposes.
>> > 
>> > After surveying the computing hardware available, a Sun Ultra10 seems to 
>> > keep the best time and is otherwise unused.
>> > 
>> > What OS do you recomend for the Ultra? Off the top of my head, I'm 
>> > considering Solaris (is there PPS support in Solaris 10?), FreeBSD or 
>> > NetBSD. My understanding is Linux 2.6 PPS support is rough at best.
>> FreeBSD is the canonical OS for a PPS box, search for some of phk's 
>> articles on this subject!

>Seconded. FreeBSD has taken ntp and timing as a priority for a very long
>time. I know that back in the days when BSD was still being developed at
>Berkeley, they counted the instructions used by the PPS kernel code and
>then used the clock frequency to correct the time for that delay.

That is of course less of an issue with CPUs running at 2GHz than it was
for CPUs running at 40KHz.

>N.B., with any system, don't expect really good time if the CPU uses
>power management tools that change the frequency of the CPU while NTP is
>running. Your probably better off with a single CPU system.

Should be OK if the system uses something like HPET for the timing rather
than cpu instruction cycles. Mind you on linux, the whole timing routines
are in a bit of a mess right now it seems. But maybe that is also true of

>R. Kevin Oberman, Network Engineer
>Energy Sciences Network (ESnet)
>Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
>E-mail: oberman at es.net			Phone: +1 510 486-8634
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