I've found that setting Minpoll and Maxpoll to 5 gives me best results. Rob
-----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Anders Wallin Sent: 29 September 2013 13:11 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] refclock -> NTP server settings/tuning? Thanks for all replies, I can try changing maxpoll to a larger value and see if the trace is smoother. The refclock driver is a userspace C-program (daemon) that essentially does: while(1) { gettimeofday(&tv,NULL) // system time, for NTP receiveTimeStamp get_wr_time(&wr_tv); // WR time, for NTP clockTimeStamp // write tv and wr_tv to shared memory where NTP expects to see them sleep(8); } This may be the cause of a constant negative offset I see, since one time-stamp is always read before the other. Perhaps this could be improved by reading system time both before and after get_wr_time() and reporting the average of the two readings as receiveTimeStamp? Or measure the offset and put it as a "time1" offset-value in ntp.conf If the driver was written as a kernel module, would that run with higher priority and less variable delay? I use the same piece of code to log how well system time tracks WR-time. Here I sometimes see sudden spikes of 100s of microseconds. Could this be caused by the OS context switching in the middle of my program between the two timestamp-reading functions? Again, would this improve if the time-logger was written as a kernel module, or is there some other way of coding it that avoids context switches and keeps the two time-stamp reading functions "atomic"? Standard Ubuntu nowadays has a pre-packaged "lowlatency" kernel which I think is RT-Preempt with some modifications. But I assume both the refclock-driver and the logger would need a re-write to take advantage of the RT-kernel. Does anyone have experienced with that? thanks, Anders _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
