StupidOS/boot/loader/a20.inc

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; 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
2024-02-06 14:20:27 +00:00
ret