[ntp:questions] Sure GPS - Very High Jitter and Offset
Miroslav Lichvar
mlichvar at redhat.com
Tue Aug 16 14:53:37 UTC 2011
On Tue, Aug 16, 2011 at 09:42:09AM -0500, Ken Link wrote:
> I wrote a script to compare the previous/current assert timestamp
> (ignoring the seconds), and this is what I get when NTP is *not*
> running:
>
> -.000004357
> -.000007328
> -.000008905
> -.000007969
> -.000007593
> -.000009174
> -.000006566
> -.000008152
> -.000007500
> -.000006854
That looks good.
> I tried setting flag3 to 0 but it didn't appear to make a difference.
> Also, I would have expected NTP to mark the clock as a PPS source with
> 'o', but when I let it sync it seems to stick with '*' instead:
>
> $ ntpq -p
> remote refid st t when poll reach delay offset jitter
> ==============================================================================
> LOCAL(0) .LOCL. 12 l 232 64 10 0.000 0.000 0.002
> *GPS_NMEA(0) .GPS. 0 l 7 16 377 0.000 20.012 26.423
It seems the GPS driver is not getting or is ignoring the PPS signal.
I think there were some issues fixed recently in it. I'd try the ATOM
driver (22) first to verify ntpd was compiled with PPS support and is
able to use it.
--
Miroslav Lichvar
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