Re: Cyrix 6x86MX and Centaur C6 CPUs in 2.1.102

C. Scott Ananian (
Fri, 22 May 1998 06:04:33 -0400 (EDT)

On Fri, 22 May 1998 (Rogier Wolff) wrote:

> James Mastros wrote:
> > Then again,
> > if it deviates from the Intel chips on an undefined matter, or goes above
> > and beyond the call of duty, then the chip is better then the Intel
> > "equivlent" in that respect, and we should take advantage of those features
> > as best as we can.
> In this case, I think Cyrix did the right thing. They added a feature,
> (powerdown the CPU as much as possible when not doing anything else).
> Now they found out that the Intel specs (indirectly) say the TSC needs
> to keep running. So... they made their feature an option. If your OS
> isn't prepared to take the consequenses of the added feature, don't
> turn it on. Simple.

I hate to have to keep bringing this up: the Cyrix problem is not an
'added feature.' They destroy the top 32-bits of the TSC on HLT. We're
not talking about "the TSC stops when the processor clock stops" which is
entirely valid (although also problematic for the kernel---this is another
issue entirely). To their credit, it appears that you can disable this
behaviour. But there's no good reason for destroying register contents; I
find it very hard to call this a 'feature'.
@ @
C. Scott Ananian: / Declare the Truth boldly and
Laboratory for Computer Science/Crypto / without hindrance.
Massachusetts Institute of Technology /META-PARRESIAS AKOLUTOS:Acts 28:31
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