cvs commit: src/sys/conf options.i386 src/sys/i386/i386 tsc.c src/sys/i386/conf NOTES

[Peter Jeremy]

On Mon, Apr 07, 2003 at 10:58:07AM +0200, Poul-Henning Kamp wrote:
>The best result I have had so far, and the only one I have sufficient
>faith in to advocate its use in general, takes an entirely different
>route:
>
>The RTC interrupts us at 128Hz for statclock, divide this in software
>to get 1Hz and take timestamps and feed them to the NTP kernel-FLL code
>and tell NTPD to lock to that at a high stratum.  

Given that this clock is effectively free-running compared to real time,
could this cause the kernel clock to jump if ntpd switches to/from this
clock source?

Do you have patches available to do this?  I know I did something
similar in 2.2 but never keep the code up to date and I think I've
lost it.

>[1] fun fact:  The 14.318MHz is four times the color burst frequency
>of NTSC television signals,

fun fact 2: 4.77MHz is 14.318MHz/3.  The divide-by-3 is because the
i8284 (8086/88 clock generator chip) divides the crystal by 3 to
generate the system clock.  This means the CGA could use the crystal
on the motherboard (though I don't know if it did actually use the
ISA clock).

> and was chosen by IBM for the original
>IBM PC because it made it possible to generate four different colors
>in a purely digital fasion on a television connected to the CGA.

I think Apple was the first to make use of this.

Peter