[ntp:questions] Slow convergence of NTP with GPS/PPS
Richard B. Gilbert
rgilbert88 at comcast.net
Tue Sep 30 19:03:39 UTC 2008
David McConnell wrote:
> We are using Linux ntpd with GPS/PPS reference clock to discipline the time
> on our systems.
> Our application requires good time accuracy (better than 5ms) but it also
> needs to get there quickly (as quickly as possible, but ideally taking no
> more than about 15 minutes).
> (The Linux/ntpd is running on a remote embedded device that is frequently
> restarted - possibly once a day or so - so we cant wait hours for
> Currently ntpd can take hours to achieve the desired acuracy.
> So, the question is simple - is there any way to significantly speedup the
> convergence of ntpd (using GPS/PPS reference clock)?
If you are using a recent version of ntpd, start it with the "-g"
switch. That will cause it to set the clock to the correct time once
only! If you have a good drift file, you should be synchronized in
thirty seconds or so and be within ten milliseconds, or less, of the
Try not to reboot unless absolutely necessary. I realize that some
versions of Windows need fairly frequent reboots but there are are
versions that should run for many days or weeks between reboots. My
desktop system is W/XP SP2 and has been up for at least a couple of
months and may stay up for another couple of months.
More information about the questions