Hi James, We have done some measurements of the stability of the STC clocksource that the kernel relies on to build its system clock. I believe this link could be the answer to your question: http://www.synclab.org/?post=blog/2012/11/radclock-raspberry-stability-nic-noise.html
Please note that these measurements are made with our custom kernel patches and bypass any kernel system clock PLL driven by ntpd. So the results have to be interpreted in this context -- especially, they do not rely on the nominal frequency reported by the clocksource. Cheers, Julien On 25/07/2013, at 1:21 PM, James Peroulas <[email protected]> wrote: > I was hoping to measure the ppm error of a Raspberry Pi's crystal using an > NTP client running on the Pi itself. The NTP client reports a ppm > correction that I find to be consistently (measurements performed over > several days) off by about 10 ppm compared to what I measure using my GPS > calibrated frequency counter (HP5328). Specifically, the Pi reports a > required ppm correction of -33 ppm whereas I consistently measure a > required correction of -43 ppm on my frequency counter. > > Any ideas on where I can look to track down the discrepancy? Perhaps the > timers on the RPi are configured incorrectly in the kernel? Or is this the > best I can expect from NTP? I would understand the situation if the NTP > reported correction drifted above and below -43ppm, but it seldom departs > from -33ppm by more than 1 or 2 ppm... > > Thanks, > James > > P.S. I apologize if this isn't time-nutty enough :) I only need about 1ppm > accuracy in my corrections :) > > -- > *Integrity is a binary state - either you have it or you don’t.* - John > Doerr > _______________________________________________ > 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. _______________________________________________ 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.
