Those sub 1 u-second numbers are very good. They argue for using the BBB as an NTP server but I wonder if it really is the best. I think the numbers that matter are measures of the close on the computers who use your BBB as a server. In other words the goal is to synchronize a set of computers. Can The little BBB push accurate time out to a set of user computers and keep then in sync better then some other NTP server platform?
On Wed, Dec 10, 2014 at 5:58 PM, Dan Drown <[email protected]> wrote: > Quoting Paul <[email protected]>: > >> Using a PRU seems like overkill if all you want from the BBB is NTP. The >> standard pps-gpio should move the system clock precision below >> system/network jitter (.5 to 1 microsecond). The next step is using a >> timer (TIMER4) which should get you into .1 microsecond offsets. >> > > As a note to people wanting to use the timer hardware on the BBB - I have > a driver for it at https://github.com/ddrown/pps-gmtimer > > I wrote up the results in using it at http://blog.dan.drown.org/ > beaglebone-black-timer-capture-driver/ > > The summary of it is: > > pps-gpio - 50% of the time local clock offset within +/- 0.07us, 98% > within +/- 0.61us > > pps-gmtimer - 50% of the time local clock offset within +/- 0.04us, 98% > within +/- 0.43us > > Also, if you're using pps-gpio, you might want to disable cpufreq and > force your processor to 1GHz. It'll help with interrupt latency and jitter. > > cpufreq ondemand, 300MHz-1GHz - http://dan.drown.org/bbb/run9/ > interrupt-latency.png > 98% of interrupts handled 12.92us-23.21us after the event happened. > > cpufreq forced 1GHz - http://dan.drown.org/bbb/run8/interrupt-latency.png > 98% of interrupts handled 6.04us-8.58us after the event happened. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
