Hello David, On Tuesday, July 22, 2008 at 7:45:06 +0100, David Woolley wrote:
> Serge Bets wrote: >> Hwclock 2.33 sets the RTC with typically a maximum error of >> 10 microseconds > That would only be possible if the RTC's counter was updated on both > phases of the 32kHz clock, which I rather doubt. Excellent example, Dave! The source 32K crystal period being 30 µs, you point the finger at a real issue. An issue that has been squashed some time ago by hwclock's feedback mechanism. Not a problem anymore. For simplification, I'll assume everything else is instant and perfect, and will neglect RTC restart delay. When we set the RTC, the last crystal pulse happened between 0 and 30 µs ago. Let's pick 18 µs for the example. This last pulse becomes the start of this RTC second, the next second will start 32768 pulses later, and so on. Result: the RTC is in advance by +18 microseconds. Problem. However the feedback mechanism measures this +18 µs offset, and corrects future readouts by -18. Final result: nothing less than perfection. :-) Serge. -- Serge point Bets arobase laposte point net _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions