Commit a6750cb2 authored by Mathieu Maret's avatar Mathieu Maret

Go into 32bits protected mode

parent 868278ff
......@@ -70,5 +70,75 @@ boot:
call println
add sp, 2
; Switch in 32bits Protected mode
; Activate A20 http://wiki.osdev.org/A20_Line to be able to access more than 1Mb memory
mov ah, 0h
mov ax, 0x2401
int 0x15
; Change video mode to display VGA
mov ax, 0x3
int 0x10
cli ; clear interruption flag
; switch in 32 bits
lgdt [gdt_pointer] ; switch in 32bits here
mov eax, cr0
or eax,0x1; set the protected mode bit on special CPU reg cr0
mov cr0, eax
jmp CODE_SEG:boot2
; GDT table desciption could be found http://wiki.osdev.org/Global_Descriptor_Table
; here we define the 3 64bits segment needed: null segment, code segment and data segment
gdt_start: ;null segment
dq 0x0
gdt_code: ;code segment
dw 0xFFFF
dw 0x0
db 0x0
db 10011010b
db 11001111b
db 0x0
gdt_data:
dw 0xFFFF
dw 0x0
db 0x0
db 10010010b
db 11001111b
db 0x0
gdt_end:
gdt_pointer:
dw gdt_end - gdt_start
dd gdt_start
CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start
bits 32
boot2:
mov ax, DATA_SEG
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esi,hello32
mov ebx,0xb8000 ; Cannot use BIOS anymore, use VGA Text buffer instead
.loop32:
lodsb
or al,al
jz halt
or eax,0x0100 ; blue bg
mov word [ebx], ax
add ebx,2
jmp .loop32
halt:
cli
hlt
hello32: db "Hello world!",0
times 510 - ($ - $$) db 0 ; fill up to 510 with 0
dw 0xAA55 ; MBR magic number
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