[ntp:questions] Meinberg NTP monitor, silly question
Dave Hart
davehart at gmail.com
Sun Dec 20 06:52:58 UTC 2009
On Dec 20, 00:32 UTC, G8KBV wrote:
> But what does 'o' mean?
It means the PPS peer, and when present effective trumps any * seen.
> The "Application Log" shows:-
> Using user-mode PPS timestamp for GPS_NMEA(2) Not that I think it'll
> make any significant difference, but I thought I'd set all this up so
> that the PPS thing would run in Kernel mode, but obviously not.
So 127.127.20.2 (NMEA) is using the user-mode hack to get DCD
timestamps, which is only effective when you restrict the GPS to one
sentence per second. However, 127.127.22.2 (atom/PPS) is using real
kernel-mode PPSAPI timestamps. In this configuration, NMEA is
"numbering the seconds" with its sloppier timestamps, and once its
offset is under .4s, the PPS refclock takes over with its interrupt-
time timestamps.
> State Remote Refid Stratum Type When Poll
> Reach Delay Offset Jitter
> * 127.127.20.2 GPS 0 Local clock 9 16 377
> 0.000 0.089 0.006
> o PPS(2) PPS 0 Local clock 8 16 377
> 0.000 0.124 0.004
The jitter figures are nice and low for Windows. I would hope the
offset to PPS(2) would eventually be trimmed to 25us or less, and even
with temperature swings you might hope to keep within 150-200us at
worst.
Cheers,
Dave Hart
More information about the questions
mailing list