[time-nuts] Beaglebone NTP server
Graham / KE9H
ke9h.graham at gmail.com
Wed Dec 10 21:54:17 EST 2014
When you forced/locked the CPU frequency at 1 GHz, did you by any chance
measure what it did to the CPU case/package temperature? Or current drain?
I note that you used BBB pin P8.7 for PPS input. That allowed you to use
it for either
pps-gpio or TIMER4 pps-gmtimer, by just changing the pin-mux?
On Wed, Dec 10, 2014 at 7:58 PM, Dan Drown <dan-timenuts at drown.org> wrote:
> Quoting Paul <tic-toc at bodosom.net>:
>> 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/
> 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/
> 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.
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