Date: Wed, 1 Nov 1995 10:00:29 +0200 (SAT) From: John Hay <jhay@mikom.csir.co.za> To: wollman@lcs.mit.edu (Garrett A. Wollman) Cc: current@FreeBSD.org Subject: Re: Time problems Message-ID: <199511010800.KAA18894@zibbi.mikom.csir.co.za> In-Reply-To: <9510311747.AA29686@halloran-eldar.lcs.mit.edu> from "Garrett A. Wollman" at Oct 31, 95 12:47:55 pm
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OK, I changed the values in calibrate_cyclecounter() like suggested and now
my time stay much closer to reality.
My CPU even probe as a 90MHz processor!
> CPU: 90-MHz Pentium 735\\90 (Pentium-class CPU)
> Origin = "GenuineIntel" Id = 0x525 Stepping=5
> Features=0x3bf<FPU,VME,PSE,MCE,CX8,APIC>
Can we get some kernel config option to do this or will I have to change
clock.c after every ctm? Or will this get to be the default?
John
--
John Hay -- John.Hay@csir.co.za
> In talking to David Greenman about this problem, we found that one of
> his machines which exhibits this problem suffers from (1). Other
> people have suggested (2) for their motherboards. (David's
> motherboard took about 12 seconds to perform a ten-second delay.)
>
> Here's one thing which you might try:
>
> In this function (in i386/isa/clock.c):
>
> ------------------------------------
> calibrate_cyclecounter(void)
> {
> /*
> * Don't need volatile; should always use unsigned if 2's
> * complement arithmetic is desired.
> */
> unsigned long long count;
>
> __asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
> DELAY(1000000);
> __asm __volatile(".byte 0xf,0x31" : "=A" (count));
> /*
> * XX lose if the clock rate is not nearly a multiple of 1000000.
> */
> pentium_mhz = (count + 500000) / 1000000;
> }
> ------------------------------------
>
> Change the occurrences of `1000000' to `10000' and `500000' to
> `5000'. This will reduce the calibration time, which makes it more
> likely that the error in your clock will be small enough to get
> rounded off. If that doesn't work, then just #ifdef out the body of
> the function, which will cause the 8254-alike to act as the reference
> for timekeeping.
>
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