;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
;   THE FOOL-BOOT-LOADER
;    
;   So we have just been loaded by the BIOS and are in 16-bits real mode!
;   Now the following work will bee accomplished (chronologically):
;
;	* BOOT_DRIVE set 
;
;	* 50 sectors of our kernel loaded at KERNEL_OFFSET from floppy
;
;	* memory map made available at MEMMAP_OFFSET 
;	    (check at MEMMEP_SIZE_OFFSET for number of entries)
;
;	* the VESA mode specified by VESA_MODE_SELECT will be set up 
;	    (check at VESA_MODES, and VESA_MODE_INFO 
;	    for additional information)
;
;	* interrupts disabled
;
;	* 32-bit protected mode set up.
;
;	* esp set to 0x90000 (Todo: take care of it!?)
;
;	* A20 gate opened (Todo: really necessary?)
;
;	* PICs configured
;
;	* and finally we will jump into the C world to kernel_main() !
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

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

;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 some constants
;where we will load our kernel into memory and some 
;other memory locations

KERNEL_OFFSET equ 0x1000
MEMMAP_SIZE_OFFSET equ 0x7c00+0x600
MEMMAP_OFFSET equ 0x7c00+0x400
VESA_MODES equ 0x8300
VESA_MODE_INFO equ 0x8400
VESA_MODE_SELECT equ 0x4114

jmp boot_16 ;start boot process

;SOME Global Data, mainly info/error strings
BOOT_DRIVE:
    db 0xff
STR_VERSION:
    db "v0.3.1~",0
VESA_CHECK1:
    db " V1.",0
VESA_CHECK2:
    db " V2",0
VESA_CHECK3:
    db " V2",0
CHECK_A20:
    db " A20",0

;lets put our temporary GDT (Global Descriptor Table) here
;kernel should move this away
%include "boot/GDT.asm"

;include 16-bit real mode routines (print_string, disk_load, vesa_setup,check_a20)
%include "boot/disk_load_16.asm"
%include "boot/check_a20_16.asm"
%include "boot/print_string_16.asm"
%include "boot/vesa_setup_16.asm"

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

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

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

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

;lets start
[bits 16]

boot_16:

    mov bx, STR_VERSION
    call print_string

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

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

    ;Load the KERNEL (52 sectors starting at sector 2)
    mov bx,KERNEL_OFFSET
    mov dh, 52
    mov dl, [BOOT_DRIVE]
    call disk_load

    ;get memory map from bios before we enter 32 bit protected mode
    mov ax,0	; set target address in es:di (0:offset)
    mov es,ax
    mov di,MEMMAP_OFFSET
    call BiosGetMemoryMap    ; this will also put the number of entries 
			    ; of the memory map at MEMMAP_SIZE_OFFSET
    
a20check:

    mov bx, STR_VERSION
    call print_string

    call check_a20
    cmp ax,0
    je a20check ;hang if a20 is disabled!

    ;VESA:  also setup vesa stuff before entering 32 bit protected mode
    call VesaSetup

    ;finally lets enter Protected mode!!!
    call switch_to_pm

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

;  we could do ALL This inside the kernel!!!!!! TODO

    ;enable A20
    ;http://www.brokenthorn.com/Resources/OSDev9.html
    ;Method 3.1: Enables A20 through keyboard controller
    ;Not all keyboard controllers support this
    ;todo: check if this has any effect at all !?!?
   ;mov al, 0xdd	; command 0xdd: enable a20
   ;mov al, 0xdf	; command 0xdf: disable a20
   ;out 0x64, al	; send command to controller

    ;pic setup
    call pic_setup

    call KERNEL_OFFSET			        ;jump into our Kernel!

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