Re: Cyrix 6x86MX and Centaur C6 CPUs in 2.1.102

Vojtech Pavlik (
Thu, 21 May 1998 18:20:01 +0200

On Thu, May 21, 1998 at 05:33:10PM -0100, André Derrick Balsa wrote:

> > Yes, but for all the chips produced up to now it is equal, and for later
> > chips we may decide based on the chip revision / manufacturer and if needed
> > apply a TSC per sec / CPU clocks per sec ratio for the respective chip to
> > get the correct CPU frequency.
> Well, in fact the TSC *is* supposed to *exactly* count CPU clock cycles,
> so I don't see what Martin means by "CPU clock speed need not be equal
> to TSC frequency".
> Please enlighten me :)

AFAIK the fact that TSC is the count of CPU cycles is not guaranteed
anywhere - there is no specifocation or databook or anything saying it. It
is guaranteed to advance forward at some constant speed, and not to give the
same the same value in 2^x years. That's all. No mention of CPU speed.

However, all current processors do maintain the 1:1 tsc speed versus CPU
clock speed ratio.


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