Date: Mon, 7 Apr 2003 19:26:02 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 tsc.c src/sys/i386/conf NOTES Message-ID: <20030407092602.GA41279@cirb503493.alcatel.com.au> In-Reply-To: <4145.1049705887@critter.freebsd.dk> References: <20030407163148.L3478@gamplex.bde.org> <4145.1049705887@critter.freebsd.dk>
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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
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