[time-nuts] beaglebone black, debian, NTP client

David J Taylor david-taylor at blueyonder.co.uk
Tue Jan 5 10:37:08 UTC 2016

On Sat, 2 Jan 2016 11:47:09 -0000
"David J Taylor" <david-taylor at blueyonder.co.uk> wrote:

> I'm also using PPS with the BBB - you even commented on my Web page!
>   http://www.satsignal.eu/ntp/BBB-vs-RPi.html

Yes, I know. But I didn't mention your webpage, because there is something
weird going on with your system. The jitter you are seeing is very high.
And it depends on the load of the OS that seems to have many unnecessary
processes running. Even if you don't use the timer unit, like Dan Drown
did, you shouldn't see a jitter higher than 2-4us on the PPS pin (that's
approximately half the interrupt latency of the BBB including 
induced latency). But yours goes up to +/-12us, ie is 6-12 times higher.

Attila Kinali

Thanks, Attila.  I'm unsure where you are getting the figures from, but the 
graph shows 2.5 µs averaged jitter:


with the reduced OS, and 2.5 to 4 µs with the fuller OS.  The peak-to-peak 
will higher than those figures, of course.

SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk
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