Messages in this thread | | | From | (Alan Cox) | Subject | Re: Booting big kernels on IBM ThinkPad 770X | Date | Wed, 2 Dec 1998 22:32:09 +0000 (GMT) |
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> 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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