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Date: Thu, 12 Sep 2002 08:23:07 +0200
From: Vojtech Pavlik <vojtech@suse.cz>
To: Horst von Brand <vonbrand@inf.utfsm.cl>
Cc: Rolf Fokkens <fokkensr@fokkensr.vertis.nl>,
       Vojtech Pavlik <vojtech@suse.cz>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] USER_HZ & NTP problems
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References: <fokkensr@fokkensr.vertis.nl> <200209112236.g8BMaMMD016898@pincoya.inf.utfsm.cl>
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In-Reply-To: <200209112236.g8BMaMMD016898@pincoya.inf.utfsm.cl>; from vonbrand@inf.utfsm.cl on Wed, Sep 11, 2002 at 06:36:22PM -0400
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On Wed, Sep 11, 2002 at 06:36:22PM -0400, Horst von Brand wrote:

> Rolf Fokkens <fokkensr@fokkensr.vertis.nl> said:
> > 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.
> 
> I'd be _really_ surprised if that number is within 1% (+-11932 or so)
> correct, an error in the last digit (0.0001%) is surely lost. 

Well, the xtal is usually to be specified with a +-50ppm error, though
many have a larger error, but not too much larger - less than 200ppm, so
you can stay surprised, it's within +-0.02% worst case. 2 at the last
place is about 1.5ppm. This is about five seconds a month.

-- 
Vojtech Pavlik
SuSE Labs
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