Date: Sat, 30 Nov 1996 01:42:00 +0800 From: Peter Wemm <peter@spinner.dialix.com> To: Erich Boleyn <erich@uruk.org> Cc: Nate Williams <nate@mt.sri.com>, Steve Passe <smp@csn.net>, freebsd-smp@freebsd.org Subject: Re: Pentium CPU steppings Message-ID: <199611291742.BAA19182@spinner.DIALix.COM> In-Reply-To: Your message of "Fri, 29 Nov 1996 08:46:59 PST." <E0vTW5b-000543-00@uruk.org>
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Erich Boleyn wrote:
> Uh... you can't just look at the "step" number. The "model" number is
> also quite relevant. The "family" is the chip design (386, 486, Pentium,
> etc.), the "model" is the major revision, and the "step" is the stepping.
> The 3 numbers are pretty much strictly ordered for severity of changes.
Ahh yes, sorry, I'd forgotten about this since it's been a while since
I've seen anything other 5/2/x.
> The fdiv bug occurs in model 1 chips with stepping less then 6 (I think,
> don't quote me). A higher stepping in the same model, or any higher model
> with any stepping is fixed.
Hmm, weren't both the P5-60/66 and the early P5-90's affected? I was
under the impression that model "1" of the "5" family was the 5V
non-clock-multiplied 60/66Mhz Pentiums? And model "2" was the improved
3.3V design with the clock multiplication and the on-chip local APIC?
Anyway, according to this C version of the Intel test assembler code,
0x521 (P5-90 in my case) has the bug:
/* be sure to disable optimisation when compiling, eg: gcc -O0 ... */
main()
{
double x = 4195835.0;
double y = 3145727.0;
double result = (x - (x / y) * y);
printf("x = %f, y = %f, result = %f, FDIV %s\n", x, y, result,
result < 1.0 ? "OK" : "BUG PRESENT");
}
peter@spinner[1:34am]~/fdiv-128> ./chk
x = 4195835.000000, y = 3145727.000000, result = 256.000000, FDIV BUG
PRESENT
peter@spinner[1:34am]~/fdiv-130> dmesg | grep Step
Origin = "GenuineIntel" Id = 0x521 Stepping=1
And on a newer P5-100 cpu:
peter@curie[4:35am]~-108> cc -O0 -o chk chk.c
peter@curie[4:35am]~-109> ./chk
x = 4195835.000000, y = 3145727.000000, result = 0.000000, FDIV OK
peter@curie[4:35am]~-110> dmesg | grep Step
Origin = "GenuineIntel" Id = 0x525 Stepping=5
Grumble.. It looks like the low steppings of "model 2" have it as well.
Damn..
Hmm, I wonder if it's safe to test for this at the end of npx.c in the
kernel?
Cheers,
-Peter
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