;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
;   THE FOOL-BOOT-LOADER
;    
;	* X 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 under MBR
;
;	* A20 gate opened 
;
;	* 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 was bootloader0
;this is where the BIOS per definition will put the first 
;512 bytes of data from the boot device
;wer are one sector after that.
[org 0x7e00]

;;define some constants
;;where we will load our kernel into memory and some 
;;other memory locations
;
MEMMAP_SIZE_OFFSET equ 0x7c00
MEMMAP_OFFSET equ 0x7c01
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
KERNEL_CHUNK:
    dw 0x1
STR_VERSION:
    db "Fool Loader Stage 2 v0.5",0

STR_LOAD:
    db "Loading Kernel...",0
STR_BOOT:
    db "Boot Drive: ",0
MEMMAP_INFO:
    db "Getting Memory Map from BIOS.",0
STR_PM:
    db "PROTECTED MODE",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"

;include some pm mode helpers
%include "boot/common_pm.asm"

;
;
;
;;get memory map routine
%include "boot/memmap.asm"
;
;;;;;;;;; BOOT 16-bit real ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
;;lets start
[bits 16]

idt_real:
    dw 0x3ff	    ; 256 entries, 4b each = 1K
	dd 0		; Real Mode IVT @ 0x0000

boot_16:

    mov [BOOT_DRIVE],dl

    ;pr info 
    mov bx, STR_VERSION
    call print_string
    call print_nextline

    ;show bootdrive
    mov bx, STR_BOOT
    call print_string
    mov al,dl
    call print_hex_byte
    call print_nextline


    ; memmap message
    mov bx,MEMMAP_INFO
    call print_string
    call print_nextline

    ;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

kernel_load:
    ;   Load the KERNEL Image
    mov bx, STR_LOAD
    call print_string
    call print_nextline
    call disk_load_16

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

    ;Fast A20 Gate:
    ;http://wiki.osdev.org/A20_Line
    
    in al, 0x92
    or al, 2
    out 0x92, al


    ; tell the world we are protected
    mov ebx,STR_PM
    mov ecx,2*23*80
    call print_string_pm

    push edx ; persist edx for some reason!?

    mov edx,0
    mov dx,[KERNEL_CHUNK]
    mov ecx,2*24*80
    call print_hex_pm



    ; here we should move the chunk away or stop the loop if everything loaded.
    mov ax,[KERNEL_CHUNK]
    add ax,1
    mov [KERNEL_CHUNK],ax

	; here we should copy the chunk into ext mem!




    ; and now go back to real! (first 16bit protected!)
    cmp edx,0x20
    je finish_load
    pop edx



    jmp CODE16_SEG:reinit_16
    finish_load:
    ;

    call VesaSetup

    ; call kernel!
    mov eax,0		;tell the kernel 
			; we are the booting processor
    call 0x18000        ;jump into our Kernel!


[bits 16]
reinit_16: ;16 bit protected mode

    mov eax,DATA16_SEG
    mov ds,eax
    mov es,eax
    mov fs,eax
    mov gs,eax
    mov ss,eax


    mov eax,cr0
    and eax,!0x1    ; Disable protected mode
    mov cr0, eax

    jmp 0:realmode


realmode:

    mov sp,0x07bff
    mov bp,sp

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

    lidt [idt_real]

    sti
    jmp kernel_load