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;*******************************************************
;
;	Stage3.asm
;		THEMOS Kernel Entry
;       Stage3 is linked against the kernel.
;*******************************************************

;org 	0x100000 

bits	32				; 32 bit code

extern kernel_entry

jmp	Stage3				

%include "paging.inc" 

Stage3:

    call kernel_entry
	;---------------------------------------;
	;   Stop execution			;
	;---------------------------------------;
      
	cli
	hlt

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main:
        ;This is stage 2. The kernel is loaded into memory, we gather memory info and pass it to the kernel.
	;-------------------------------;
	;   Setup segments and stack	;
	;-------------------------------;

	cli				; Clear interrupts
	xor	ax, ax			; Null segments
	mov	ds, ax
	mov	es, ax
	mov	ax, 0x0			; Stack begins at 0x9000-0xffff
	mov	ss, ax
	mov	sp, 0xFFFF
	sti				; Enable interrupts

	mov     	[boot_info+multiboot_info.bootDevice], dl

	;-------------------------------;
	;   Install GDT		;
	;-------------------------------;

	call	InstallGDT		; Install GDT

	;-------------------------------;
	;   Enable A20			;
	;-------------------------------;

	call	EnableA20_KKbrd_Out

	;-------------------------------;
	;   Setup memory info	;
	;-------------------------------;

	xor		eax, eax
	xor		ebx, ebx
	call		BiosGetMemorySize64MB_32bit

	push		eax
	mov		eax, 64
	mul		ebx
	mov		ecx, eax
	pop		eax
	add		eax, ecx
	add		eax, 1024		; the routine doesnt add the KB between 0-1MB; add it

	mov		dword [boot_info+multiboot_info.memoryHi], 0
	mov		dword [boot_info+multiboot_info.memoryLo], eax

	mov		eax, 0x0
	mov		ds, ax
	mov		di, 0x1000
	call		BiosGetMemoryMap

	;-------------------------------;
	;   Print loading message	;
	;-------------------------------;

	mov	si, LoadingMsg
	call	Puts16

        ;-------------------------------;
        ; Initialize filesystem		;
        ;-------------------------------;

	call	LoadRoot		; Load root directory table

        ;-------------------------------;
        ; Load Kernel			;
        ;-------------------------------;

	mov	ebx, 0			; BX:BP points to buffer to load to
    mov	bp, IMAGE_RMODE_BASE
	mov	si, ImageName		; File to load
	call	LoadFile		; Load file
	mov	dword [ImageSize], ecx	; Save size of kernel
	cmp	ax, 0			; Test for success
	je	EnterStage3		; Yep--onto Stage 3!
	mov	si, msgFailure		; Nope--print error
	call	Puts16
	mov	ah, 0
	int     0x16                    ; Await keypress
	int     0x19                    ; Warm boot computer
   	cli				             ; Overkill...
	hlt

	;-------------------------------;
	;   Go into pmode		;
	;-------------------------------;

EnterStage3:

	cli				; Clear interrupts
	mov	eax, cr0		; Set bit 0 in cr0--enter pmode
	or	eax, 1
	mov	cr0, eax
	
	jmp	CODE_DESC:Stage3	; Far jump to fix CS. Code selector is 0x8!

;******************************************************
;	ENTRY POINT FOR STAGE 3
;******************************************************

bits 32

Stage3:

	;-------------------------------;
	;   Set registers		;
	;-------------------------------;

	mov	ax, DATA_DESC	; Set data segments to data selector (0x10)
	mov	ds, ax
	mov	ss, ax
	mov	es, ax
	mov	esp, 90000h		; Stack begins from 90000h

	;-------------------------------;
	; Copy kernel to 1MB		;
	;-------------------------------;

CopyImage:
  	 mov	eax, dword [ImageSize]
  	 movzx	ebx, word [bpbBytesPerSector]
  	 mul	ebx
  	 mov	ebx, 4
  	 div	ebx
   	 cld
   	 mov    esi, IMAGE_RMODE_BASE
   	 mov	edi, IMAGE_PMODE_BASE
   	 mov	ecx, eax
   	 rep	movsd                   ; Copy image to its protected mode address

	;-------------------------------;
	; Push boot info	;
	;-------------------------------;

	push dword boot_info

	;---------------------------------------;
	;   Execute Kernel			;
	;---------------------------------------;

	jmp	CODE_DESC:IMAGE_PMODE_BASE; Jump to kernel! Note: This assumes Kernel's entry point is at 1 MB

	;---------------------------------------;
	;   Stop execution			;
	;---------------------------------------;

	cli
	hlt

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void kernel_entry(multiboot_info* bootinfo)
{
}

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;*******************************************************
;
;	paging.inc
;		Common Paging Methods
;*******************************************************

%ifndef __PAGING_INC_INCLUDED__
%define __PAGING_INC_INCLUDED__

bits 32

; Read the CR0 register.
global read_cr0
read_cr0:
    mov eax, cr0
    retn

; Write the CR0 register.
global write_cr0
write_cr0:
    push ebp
    mov ebp, esp
    mov eax, [ebp+8]
    mov cr0, eax
    pop ebp
    retn

; Read the CR3 register.
global read_cr3
read_cr3:
    mov eax, cr3
    retn

; Write the CR3 register.
global write_cr3
write_cr3:
    push ebp
    mov ebp, esp
    mov eax, [ebp+8]
    mov cr3, eax
    pop ebp
    retn


%endif

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mov eax, cr0
or eax, 1
mov cr0, eax

mov eax, cr0
or eax, 0x80000000
mov cr0, eax

mov eax, page_directory
mov cr3, eax