Tom, The RTC typically has a wristwatch type 32,768 kHz resonator. This is independent to the oscillator setting bus and processor speed. They have common factors in temperature and other environment, but nothing steering them together.
You can have more independent oscillators, so things can drift away in "interesting" ways. A fun exercise is to take timestamps of different timestampers and locking one oscillators in reference to another. Then one can follow the variations in frequency error in easy form. Otherwise just plot the phase-difference and toss into TimeLab. Cheers, Magnus On 2021-01-06 14:16, Tom Holmes wrote: > Am I missing something or maybe I don't understand > the situation , but I am under the impression that > the RTC has it's own battery and crystal unrelated > to the processor clock. Seems like in that case, > the 24 MHz won't have any effect on the > timekeeping drift. > > Tom Holmes, N8ZM > > -----Original Message----- > From: time-nuts <[email protected]> > On Behalf Of Trent Piepho > Sent: Wednesday, January 06, 2021 6:03 AM > To: Discussion of precise time and frequency > measurement <[email protected]> > Subject: Re: [time-nuts] x86 CPU Timekeeping and > clock generation > > On Tue, Jan 5, 2021 at 9:42 PM Luiz Paulo Damaceno > <[email protected]> wrote: >> The 24 MHz comes from an synthesizer that is > locked to an atomic clock, the >> clock of NTP server (also 24 MHz, but an > embedded board (Tinkerboard)) also >> comes from the same Atomic clock that is feeding > other synthesizer for >> generates 24 MHz to this board. > The RK3288 has some PWM generators. These are of > course also fed from > PLLs derived from the same 24 MHz input. > > So, why not produce a signal on the PWM that can > be compared to your > reference? This would tell you if the error is in > the clock > generation on the SoC or something in software > that happens afterward. > Or at least as far as the PWM clock tree overlaps > the kernel > timesource clock tree, which could be the CPU > clock but it can be > other things too. > >> The experiment is the following: 1- synchronize > the computer's clock to NTP >> server then leave it running free (no periodic > synchronization), 2 - > > NTP will set the frequency skew too, so even if it > is not doing > periodic synchronization, there may still be a > programmed frequency > skew. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_l > ists.febo.com > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
