[bits 16]
[org 0x7c00]

bootld_start:
    KERNEL_OFFSET equ 0x2000

    xor ax, ax      ; Explicitly set ES = DS = 0
    mov ds, ax
    mov es, ax
    mov bx, 0x8C00  ; Set SS:SP to 0x8C00:0x0000 . The stack will exist
                    ;     between 0x8C00:0x0000 and 0x8C00:0xFFFF
    mov ss, bx
    mov sp, ax

    mov [BOOT_DRIVE], dl

    mov bx, boot_msg
    call print_string

    mov dl, [BOOT_DRIVE]
    call disk_load

    jmp pm_setup

    jmp $

BOOT_DRIVE:
    db 0

disk_load:
    mov si, dap
    mov ah, 0x42

    int 0x13

    ;cmp al, 4
    ;jne disk_error_132

    ret

dap:
    db 0x10             ; Size of DAP
    db 0
    ; You can only read 46 sectors into memory between 0x2000 and
    ; 0x7C00. Don't read anymore or we overwrite the bootloader we are
    ; executing from. (0x7c00-0x2000)/512 = 46
    dw 46               ; Number of sectors to read
    dw KERNEL_OFFSET    ; Offset
    dw 0                ; Segment
    dd 1
    dd 0

disk_error_132:
    mov bx, disk_error_132_msg
    call print_string

    jmp $

disk_error_132_msg:
    db 'Error! Error! Something is VERY wrong! (0x132)', 0

gdt_start:

gdt_null:
    dd 0x0
    dd 0x0

gdt_code:
    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_descriptor:
    dw gdt_end - gdt_start
    dd gdt_start

CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start

boot_msg:
    db 'OS is booting files... ', 0

done_msg:
    db 'Done! ', 0

%include "boot/print_string.asm"

pm_setup:
    mov bx, done_msg
    call print_string

    mov ax, 0
    mov ss, ax
    mov sp, 0xFFFC

    mov ax, 0
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax

    cli
    lgdt[gdt_descriptor]
    mov eax, cr0
    or eax, 0x1
    mov cr0, eax
    jmp CODE_SEG:b32

    [bits 32]

    VIDEO_MEMORY equ 0xb8000
    WHITE_ON_BLACK equ 0x0f

    print32:
        pusha
        mov edx, VIDEO_MEMORY
    .loop:
        mov al, [ebx]
        mov ah, WHITE_ON_BLACK
        cmp al, 0
        je .done
        mov [edx], ax
        add ebx, 1
        add edx, 2
        jmp .loop
    .done:
        popa
        ret

    b32:
        mov ax, DATA_SEG
        mov ds, ax
        mov es, ax
        mov fs, ax
        mov gs, ax
        mov ss, ax

        ; Place stack below EBDA in lower memory
        mov ebp, 0x9c000
        mov esp, ebp

        mov ebx, pmode_msg
        call print32

        call KERNEL_OFFSET

        jmp $

    pmode_msg:
        db 'Protected mode enabled!', 0

kernel:
    mov ebx, pmode_msg
    call print32
    jmp $

pmode_tst:
    db 'Testing...'

times 510-($-$$) db 0
db 0x55
db 0xAA