Re: i387/FPU init issues...

[H. Peter Anvin]

Arjan van de Ven wrote:
> > It has retroactively been added to the documented list for all P6 core 
> > chips - that should mean it works on all of them.  The most common 
> > reason for not documenting something (other than various Pure Evil NDA 
> > schemes) is that it hasn't been properly verified.  However, 
> > verification can be done a posteori.
>
> the other reason is that certain groups of "unknown" opcodes will act as 
> NOP.
> Which for this purpose is .. exactly the right thing retroactive

Specifically, I believe the P6 added a whole class of instructions which 
would act as NOP's if used on older chips.  It has been used for 
prefetch instructions, etc.  At some point, the 0F 1F /0 group was 
declared to be NOP, and nothing else, for all future.

	-hpa

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