キーボードコントローラーによりA20以上のアドレスバスを有効にする

code:enable_a20_by_kbd.asm

kbd_io_data equ 60h

kbd_io_cmd equ 64h

kbd_io_status equ 64h

kbd_cmd_disable_kbd equ 0adh

kbd_cmd_enable_kbd equ 0aeh

kbd_cmd_read_port2 equ 0d0h

kbd_cmd_write_port2 equ 0d1h

kbd_status_in_ready_mask equ 01h

kbd_status_out_not_ready_mask equ 02h

kbd_port2_gatea20_mask equ 02h

enable_a20_by_kbd:

cli

call wait_kbd_for_out

mov al, kbd_cmd_disable_kbd

out kbd_io_cmd, al

call wait_kbd_for_out

mov al, kbd_cmd_read_port2

out kbd_io_cmd, al

call wait_kbd_for_in

in al, kbd_io_data

push ax

call wait_kbd_for_out

mov al, kbd_cmd_write_port2

out kbd_io_cmd, al

call wait_kbd_for_out

pop ax

or al, kbd_port2_gatea20_mask

out kbd_io_data, al

call wait_kbd_for_out

mov al, kbd_cmd_enable_kbd

out kbd_io_cmd, al

call wait_kbd_for_out

sti

ret

wait_kbd_for_out:

in al, kbd_io_status

test al, kbd_status_out_not_ready_mask

jnz wait_kbd_for_out

ret

wait_kbd_for_in:

in al, kbd_io_status

test al, kbd_status_in_ready_mask

jz wait_kbd_for_in

ret

参考