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;; boot.stage2.a20.asm
_enable_a20:
cli
;; Disable keyboard
call .wait_io1
mov al, 0xad
out 0x64, al
;; Read from keyboard controller
call .wait_io1
mov al, 0xd0
out 0x64, al
call .wait_io2
in al, 0x60
push eax ; Save current value
;; Write back with the A20 bit set
call .wait_io1
mov al, 0xd1
out 0x64, al
call .wait_io1
pop eax
or al, 2 ; Set A20 bit
;; Enable keyboard
call .wait_io1
mov al, 0xae
out 0x64, al
call .wait_io1
.wait_io1:
in al, 0x64
test al, 2
jnz .wait_io1
ret
.wait_io2:
in al, 0x64
test al, 1
jz .wait_io2
ret
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