Messages in this thread |  | | Date | Tue, 10 Sep 2002 08:48:53 +0200 | From | Vojtech Pavlik <> | Subject | Re: [PATCH] USER_HZ & NTP problems |
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On Tue, Sep 10, 2002 at 08:37:17AM +0200, Rolf Fokkens wrote: > On Tuesday 10 September 2002 08:09, Vojtech Pavlik wrote: > > Actually, the clock true frequency is 1193181.8 Hz, although most > > manuals say 1.19318 MHz, which, because truncating more digits, also > > correct. But 1193180 Hz isn't. If you're trying to count the time > > correctly, you should better use 1193182 Hz if staying in integers. > > I copied the clock frequency from the kernel source, timex.h defines: > > #define CLOCK_TICK_RATE 1193180 > > If what you're saying is correct, timex.h uses the wrong value as wel I guess.
Yes, it uses the wrong value.
It's not too big a difference to notice, the error in the frequency from the ideal value in most cheap mainboard crystals is greater than 2 Hz. So it's lost in the noise.
The clock is generated from a base crystal of 14.3181818 by division by 12. The base crystal is the frequency found on ISA for the MDA/CGA adapters, and is a NTSC dot-clock. All other frequencies on a motherboard (except the RTC, which has a separate 32.000 kHz clock) are derived from it.
It's just if you try to get the computations correct, you may also want to have this value correct. :)
-- Vojtech Pavlik SuSE Labs - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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