[time-nuts] Beaglebone NTP server

Dan Drown dan-timenuts at drown.org
Thu Dec 11 09:45:46 EST 2014

The CPU temperature as measured by the on-CPU sensor went from about  
55C to about 60C.

300MHz to 1GHz, ondemand, CPU in red http://dan.drown.org/bbb/run9/temp.png

1GHz fixed, CPU in red http://dan.drown.org/bbb/run8/temp.png

For current drain, I only have numbers at the wall wart measured by a  
kill-a-watt.  The entire system goes from 0.02A/1W to 0.04A/2W.  Power  
Factor is in the 0.5~0.4 region.

For the pins, that is correct. I chose P8.7 because it was TIMER4's  
input, and I can switch between pps-gpio and pps-gmtimer by changing  
which dts overlay I'm using.

Quoting Graham / KE9H <ke9h.graham at gmail.com>:
> 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?
> --- Graham
> ==
> 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/
>> 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.
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