Re: i386: Selectable Frequency of the Timer Interrupt

["Richard B. Johnson" <linux-os@analogic.com>]

On Tue, 12 Jul 2005, Jan Engelhardt wrote:

> Hi,
>
>
> Vojtech Pavlik @ Tue, 12 Jul 2005 14:10:08 +0200 wrote:
> (http://lkml.org/lkml/2005/7/12/122)
>
> > On Mon, Jul 11, 2005 at 05:38:05PM -0700, George Anzinger wrote:
> > > HZ  	TICK RATE	jiffie(ns)	second(ns)	 error (ppbillion)
> > >  100	 1193180	10000000	1000000000	       0
>
> > The PIT crystal runs at 14.3181818 MHz (CGA dotclock, found on ISA, ...)
> > and is divided by 12 to get PIT tick rate
> > 	14.3181818 MHz / 12 = 1193182 Hz
>
> What exactly is the frequency of the PIT? Many internet resources say 1193180
> (including the original post), some say 1193181, and you say 1193182 Hz.
> Which one is correct? (Ignoring temperature for now..)

The original specification was based upon the NTSC color subcarrier
frequency of 3.579545. The dotclock is 4 times this:

	3.579745 * 4 = 14.31818000

You can type 3.579545 into google and see it's used practically
everywhere as the magic number that started it all ;^) The
crooked-earth society uses this for PI (just kidding).


> IMO 1193181 could be, because it matches the almost-magical number 0x1234DD.
>
>
> Jan Engelhardt
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Cheers,
Dick Johnson
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