use16

org 0x7c00

boot:
        jmp 0x0000:start
start:
        mov ax,0x4F02
        mov bx,0x4118
        int 0x10

        cli
        xor ax,ax
        mov ds,ax
        lgdt fword [GDTRI]
        in al, 0x92
        or al, 2
        out 0x92, al
        mov al,0x8F
        out 0x70,al
        in al,0x71
        mov eax, cr0
        or al, 1
        mov cr0, eax
        jmp 0x8: protected_mode

use32

protected_mode:
        mov ax,16
        mov ds,ax
        mov es,ax
        mov ax,24
        mov ss,ax
        mov esp,0xB7FFF
        mov  edi,0xA0000
        mov cx,65535
loop1:
        mov byte [es:edi],255
        inc edi
        loop loop1
        mov cx,65535
loop2:
        mov byte [es:edi],255
        inc edi
        loop loop2
exit:
        hlt
        jmp exit

;-------------------------------------------------

align 8

GDT:
GDT0:
    dq 0

GDT1:
    dw 0xFFFF    ;15...0    predel 15...0
    dw 0         ;31...16   adress 15...0
    db 0         ;39...32   adress 23...16
    db 10011000b ;47...40   P DPL S tip A
    db 11001111b ;55...48   G D X Y predel 19...16
    db 0         ;63...56   adress 31...24

GDT2:
    dw 0xFFFF
    dw 0
    db 0
    db 10010100b
    db 11001111b
    db 0

GDT3:
    dw 0x7FFF
    dw 0x77FF    ; 0xB8000-2048-1
    db 0xB       ;/
    db 10010110b
    db 11001010b
    db 0

GDTRI:
    dw GDTRI-GDT0-1
    dd GDT

;-------------------------------------------------

finish:
times 0x1FE-finish+boot db 0
db   0x55, 0xAA

;------------------------------------------------------------------------------
;++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
;------------------------------------------------------------------------------

org 0x7E00