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Better A20 setup

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This commit is contained in:
Robbe Van Herck 2020-01-02 12:00:50 +01:00
parent 69a76bb94d
commit afe2829849
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GPG key ID: A66F76F7B81BD784
1 changed files with 17 additions and 9 deletions
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26
bootloader/main.asm
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@ -54,9 +54,6 @@ check_a20:
;;; Print string at bx ;;; Print string at bx
puts: puts:
mov al, '!'
mov ah, 0x0e
int 0x10
.puts_loop: .puts_loop:
mov al, [bx] ; load the character mov al, [bx] ; load the character
@ -125,6 +122,14 @@ ret
.start: .start:
; set up stack
mov ax, 0
mov ss, ax
mov sp, 0x7C00
mov ds, ax
mov es, ax
; disable vga cursor ; disable vga cursor
mov ah, 0x01 mov ah, 0x01
mov ch, 0b00100000 mov ch, 0b00100000
@ -177,8 +182,15 @@ call puthex
call check_a20 call check_a20
cmp ax, 1 cmp ax, 1
je .a20_enabled je .a20_enabled
mov bx, .str_no_A20
call puts mov ah, 0x24 ; set a20 gate
mov al, 0x01 ; turn it on
int 0x15
jnc .a20_enabled
mov bl, ah
call puthex
jmp .end jmp .end
.a20_enabled: .a20_enabled:
@ -287,10 +299,6 @@ mov byte [ds:0x0B8005], 0x40
jmp .end jmp .end
.data: .data:
.str_no_A20:
db "A20 fault"
db 0
.gdt: .gdt:
dd 0 dd 0