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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?

    -hpa

    --
    <hpa@transmeta.com> at work, <hpa@zytor.com> in private!
    "Unix gives you enough rope to shoot yourself in the foot."
    http://www.zytor.com/~hpa/puzzle.txt
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