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    SubjectRe: Booting big kernels on IBM ThinkPad 770X
    Date
    > According to the Technical Reference Manual there is a special
    > control port that, among other things, controls the ability of setting
    > the A20-gate in real mode, which is initially disabled. It is bit 1 of
    > the System Control Port A (0x92).
    >
    > I inserted a call to the following routine in setup.S just before setting A20
    > and now my bzImage boots!
    >
    > !
    > ! enables a20-handling on ThinkPads while in real mode
    > !
    > ThinkPad_SCP_A:
    > in al,#0x92 ! read "System Control Port A"
    > or al,#0x02 ! Set "Alternate Gate A20" - Bit
    > out #0x92,al ! write "System Control Port A"
    > ret
    >
    > Now, I'm not an assembler programmer at all. Maybe someone could take a closer
    > look into that.


    That would make some sense. Thats the A20 active bit on the IBM PS/2 as well. (Hey
    MCA hacking finally produces something useful 8)) . It might also be generally ok
    since the great Ralf Brown interrupt list documents no other users

    Alan



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