bits 32

global start

; multiboot header
MODULEALIGN equ  1<<0  
MEMINFO     equ  1<<1
VIDEOINFO   equ  1<<2
FLAGS       equ  MODULEALIGN | MEMINFO | VIDEOINFO
MAGIC       equ  0x1BADB002
CHECKSUM    equ  -(MAGIC + FLAGS)
 
align 4
section .__mbHeader
MultiBootHeader:
	dd MAGIC
	dd FLAGS
	dd CHECKSUM

section .text

STACKSIZE equ 0x4000                  ; that's 16k.

start:
	XCHG BX, BX ; magic breakpoint

	mov ecx, eax

;    lgdt [trickgdt]
;    mov ax, 0x10;
;    mov ds, ax
;    mov es, ax
;    mov fs, ax
;    mov gs, ax
;    mov ss, ax

;    jmp 0x08:HigherHalf                                          ; NOTE: Must be absolute jump!

HigherHalf:

	; Verify booted with multiboot compliant bootloader
	mov esp, stack+STACKSIZE

	cmp ecx, 0x2BADB002
	jne .bad

	push ebx

	extern k_main
	call k_main

; Show error message, and halt system
.bad:

	extern ConsoleClear
	extern ConsoleWrite
	extern CommandOsver

	call ConsoleClear
	call CommandOsver

	mov eax, [ErrorColor]
	push eax
	push ErrorString
	call ConsoleWrite

	cli
	hlt


; some variables
ErrorString			db 0xA, "%#! Fatal error: Not booted with multiboot compliant bootloader (e.g. GRUB).", 0x0
ErrorColor			db 0x0C



; tells the assembler to include this data in the '.setup' section
section .setup

trickgdt:
	dw gdt_end - gdt - 1 ; size of the GDT
	dd gdt ; linear address of GDT

gdt:
	dd 0, 0							; null gate
	db 0xFF, 0xFF, 0, 0, 0, 10011010b, 11001111b, 0x40	; code selector 0x08: base 0x40000000, limit 0xFFFFFFFF, type 0x9A, granularity 0xCF
	db 0xFF, 0xFF, 0, 0, 0, 10010010b, 11001111b, 0x40	; data selector 0x10: base 0x40000000, limit 0xFFFFFFFF, type 0x92, granularity 0xCF

gdt_end:




; stack
section .bss
align 32
stack:
    resb STACKSIZE           ; This reserves 64KBytes of memory here