;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
;    FoolOS Boot Loader
;    
;    Copyright 2014 M.Idziorek  <m.i@gmx.at>
;    
;    we have just been loaded by the BIOS and are in 16-bits real mode!
;
;   THIS IS THE CENTRAL FILE OF THE BOOTLOADER, after we finished we
;   are inside the C kernel!
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;we want 16-bit instructions, before we switch to 32-bit protected mode.

;define origin of boot record in memory: 0x7c00
;this is where the BIOS per definition will put the first 
;512 bytes of data from the boot device
;The Boot record is identified by the last 2 magic bytes: 0xaa55 (?)
[org 0x7c00]

;define where we will load our kernel into memory
KERNEL_OFFSET equ 0x1000

[bits 16]
jmp boot_16 ;start boot process

;SOME Global Data, mainly strings
STR_VERSION:
;    db "v0.2~",0
STR_PROT:
;    db "32-bit PM",0
STR_LOADED:
;    db "loaded",0

BOOT_DRIVE:
    db 0

;lets put our temporary GDT (Global Descriptor Table) here
%include "boot/GDT.asm"

;include 16-bit real mode routines (print_string, print_hex, disk_load)
%include "boot/common.asm"

;include 32-bit Protected Mode routines (print_string_pm,print_hex_pm)
;%include "boot/common_pm.asm"

;include our routines for switching to 32-bit protected mode
%include "boot/pm.asm"

;pic mapping
%include "boot/pic.asm"

;memory map
%include "boot/memmap.asm"

;;;;;;;; BOOT 16-bit real ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;lets start
[bits 16]
boot_16:

    ;setup the stack
    mov bp,0x8000
    mov sp,bp

    ;remember BOOT_DRIVE (as was set by BIOS)
    mov [BOOT_DRIVE],dl	

    ;print FoolOS version info
;    mov bx, STR_VERSION
;    call print_string

    ;Load the KERNEL
    mov bx,KERNEL_OFFSET
    mov dh, 15
    mov dl, [BOOT_DRIVE]
    call disk_load

    ;print info message that kernel was loaded
;    mov bx, STR_LOADED
;    call print_string

    ;finally lets enter Protected mode!!!
    call switch_to_pm

;;;;;;;; BOOT 32-bit protected mode;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
[bits 32]
boot_32_pm:

    ;print info message that we are in protected mode!
;    mov ecx,160
;    mov ebx,STR_PROT
;    call print_string_pm

    ;enable A20
    ;http://www.brokenthorn.com/Resources/OSDev9.html
    ;Method 3.1: Enables A20 through keyboard controller
    mov al, 0xdd	; command 0xdd: enable a20
    out 0x64, al	; send command to controller

    ;pic setup
    call pic_setup


    call KERNEL_OFFSET			        ;jump into our Kernel it


;idt_descriptor:
;    dw idt_end-idt_start-1
;    dd KERNEL_OFFSET
;;;; DEBUGGING STUFF
;times 8 db '@'
;dw interrupt
;times 8 db '@'
;dw interrupt2
;times 8 db '@'

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;so we get identified as MBR
times 510-($-$$) db 0
dw 0xaa55

;interrupt descriptor table (hardcoded address of interrupts:)
;idt_start:
;times 33 db 0x50,0x7c,0x08,0x00,0x00,10001110b,0x0,0x0
;db 0x59,0x7c,0x08,0x00,0x00,10001110b,0x0,0x0
;times 253 db 0x50,0x7c,0x08,0x00,0x00,10001110b,0x0,0x0
;idt_end: