[time-nuts] NMEA Time
Hal Murray
hmurray at megapathdsl.net
Wed Nov 25 20:57:55 UTC 2009
SAIDJACK at aol.com said:
> thanks for the info. I am wondering how accurate their SNTP server
> with 1PPS RS-232 input is. Not sure how one would test that without
> specialized equipment..
What sort of accuracy do you want?
You aren't going to get nanosecond accuracy out of a ntp server running over
an ethernet[1]. On the other hand, sub-ms isn't hard with a good OS and/or
good software.
It's fairly easy to get a reasonable sanity check on a (s)ntp server. Just
setup a known good ntp system and have it monitor the DUT. The reference
implementation for ntp (http://www.ntp.org/) has lots of support for
collecting data.
The key step in making a PC keep good time is tweaking the clock frequency.
This is the software equivalent of the EFC on an oscillator. ntpd calls it
drift. You can use it as a thermometer.
----------
1) There is a group working on that level of accuracy. It takes special
hardware that can put a time-stamp on a packet as it leaves or arrives.
http://en.wikipedia.org/wiki/Precision_Time_Protocol
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