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SubjectRe: That horrible hack from hell called A20
Linus Torvalds wrote:
> So the "orb $2,%al ; andb $0xfe,%al" will potentially change both of
> these. And I'd feel a hell of a lot more safe, if we avoided using 0x92
> except when we find that we absolutely _have_ to.
> How about making the keyboard controller timeouts shorter, and moving all
> the 0x92 games to after the keyboard controller games. That, I feel, would
> be the safest approach: try the really old approach first (that people are
> the least likely to use as GPIO - it's just too damn painful to go through
> the keyboard controller, and the keyboard controller A20 logic is just too
> well documented, so nobody would use it for anything else).
> If the keyboard controller times out, or if A20 still doesn't seem to be
> enabled, only _then_ would we do the 0x92 testing.
> Btw, do we actually know of any machine that really needs the "and $0xfe"?
> That register really makes me nervous.

Good question. The whole thing makes me nervous... in fact, perhaps we
should really consider using the BIOS INT 15h interrupt to enter
protected mode?


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