Messages in this thread | | | Date | Thu, 17 Oct 1996 09:58:17 +0100 (GMT/BST) | From | Mike Jagdis <> | Subject | Re: Cyrix cpuid'n stuff... |
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On Wed, 16 Oct 1996, Johnny Stenback wrote:
> Yeah, but there's a way around that, there is (as posted in some > patches here a couple of times already) a way to determine if the cpu > is intel or cyrix before touching those ports are touched, it's done > by setting eflags to 0, then doing div xxx,xxx and then checking if > other than the 2:nd bit in eflags is 1, if it is then it's a some kind > of non-intel cpu (this isn't necessarily the exact way to do it but at > least it's in that direction). After this check those ports can be > safely (?) touched, I don't say that the cyrix way of configures these > registers isn't dumb but it should be doable without the possibility > to break other cpu:s...
Yeah, the Cyrix changes flags in ways that other chips don't which makes a rough and ready test. It isn't that easy to add features, especially when you are the smaller player, casting in silicon, entering a volume market where you need compatibility with all kinds of existing crap code and can't a mistake. "Should" is not a good basis for fundamental design decisions :-).
> > P.S. Someone was having problem with the magic number weren't they? > > You set the MAPEN to 1. You don't set each bit in MAPEN to 1... > > Yeah, it was me, I found out, guess if I feel STUPID. Hopefylly I will > learn (to read) from my mistakes...
Don't worry. I did exactly the same thing. It seemed _obvious_ that since MAPEN was a set of bits in a byte that they were talking about setting bits... Nope... :-(
Mike
P.S. I have the patches for Cyrix recognition and use of the variable size paging mechanism (VSPM) working happily. When I roll them into a reasonably recent kernel I'll let Linus have them. (Oh, I didn't bother differentiating between IBM and Cyrix badged parts. It doesn't seem worth the trouble to me?)
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