171 lines
3.5 KiB
PHP
171 lines
3.5 KiB
PHP
; copy/pasted from https://wiki.osdev.org/A20_Line
|
|
; .... sorry I was lazy :x
|
|
|
|
a20_get_state:
|
|
pushf
|
|
push si
|
|
push di
|
|
push ds
|
|
push es
|
|
|
|
cli
|
|
|
|
xor ax, ax
|
|
mov ds, ax
|
|
mov si, 0x500
|
|
|
|
not ax
|
|
mov es, ax
|
|
mov di, 0x0510
|
|
|
|
mov al, [ds:si] ; save old values
|
|
mov byte [.BufferBelowMB], al
|
|
mov al, [es:di]
|
|
mov byte [.BufferOverMB], al
|
|
|
|
mov ah, 1 ; check byte [0x00100500] == byte [0x0500]
|
|
mov byte [ds:si], 0
|
|
mov byte [es:di], 1
|
|
mov al, [ds:si]
|
|
cmp al, [es:di]
|
|
jne .exit
|
|
dec ah
|
|
.exit:
|
|
mov al, [.BufferBelowMB]
|
|
mov [ds:si], al
|
|
mov al, [.BufferOverMB]
|
|
mov [es:di], al
|
|
shr ax, 8
|
|
sti
|
|
pop es
|
|
pop ds
|
|
pop di
|
|
pop si
|
|
popf
|
|
ret
|
|
|
|
.BufferBelowMB: db 0
|
|
.BufferOverMB db 0
|
|
|
|
|
|
a20_query_support:
|
|
push bx
|
|
clc
|
|
|
|
mov ax, 0x2403
|
|
int 0x15
|
|
jc .error
|
|
|
|
test ah, ah
|
|
jnz .error
|
|
|
|
mov ax, bx
|
|
pop bx
|
|
ret
|
|
.error:
|
|
stc
|
|
pop bx
|
|
ret
|
|
|
|
a20_enable_keyboard_controller:
|
|
cli
|
|
|
|
call .wait_io1
|
|
mov al, 0xad
|
|
out 0x64, al
|
|
|
|
call .wait_io1
|
|
mov al, 0xd0
|
|
out 0x64, al
|
|
|
|
call .wait_io2
|
|
in al, 0x60
|
|
push eax
|
|
|
|
call .wait_io1
|
|
mov al, 0xd1
|
|
out 0x64, al
|
|
|
|
call .wait_io1
|
|
pop eax
|
|
or al, 2
|
|
out 0x60, al
|
|
|
|
call .wait_io1
|
|
mov al, 0xae
|
|
out 0x64, al
|
|
|
|
call .wait_io1
|
|
sti
|
|
ret
|
|
.wait_io1:
|
|
in al, 0x64
|
|
test al, 2
|
|
jnz .wait_io1
|
|
ret
|
|
.wait_io2:
|
|
in al, 0x64
|
|
test al, 1
|
|
jz .wait_io2
|
|
ret
|
|
|
|
; out:
|
|
; cf - set on error
|
|
a20_enable:
|
|
clc ; clear cf
|
|
pusha
|
|
mov bh, 0 ; clear bh
|
|
|
|
call a20_get_state
|
|
jc .fast_gate
|
|
|
|
test ax, ax
|
|
jnz .done
|
|
|
|
call a20_query_support
|
|
mov bl, al
|
|
test bl, 1 ; enable A20 using keyboard controller
|
|
jnz .keybord_controller
|
|
|
|
test bl, 2 ; enable A20 using fast A20 gate
|
|
jnz .fast_gate
|
|
.bios_int:
|
|
mov ax, 0x2401
|
|
int 0x15
|
|
jc .fast_gate
|
|
test ah, ah
|
|
jnz .failed
|
|
call a20_get_state
|
|
test ax, ax
|
|
jnz .done
|
|
.fast_gate:
|
|
in al, 0x92
|
|
test al, 2
|
|
jnz .done
|
|
|
|
or al, 2
|
|
and al, 0xfe
|
|
out 0x92, al
|
|
|
|
call a20_get_state
|
|
test ax, ax
|
|
jnz .done
|
|
|
|
test bh, bh ; test if there was an attempt using the keyboard controller
|
|
jnz .failed
|
|
.keybord_controller:
|
|
call a20_enable_keyboard_controller
|
|
call a20_get_state
|
|
test ax, ax
|
|
jnz .done
|
|
|
|
mov bh, 1 ; flag enable attempt with keyboard controller
|
|
|
|
test bl, 2
|
|
jnz .fast_gate
|
|
jmp .failed
|
|
.failed:
|
|
stc
|
|
.done:
|
|
popa
|
|
ret |