; 
; Copyright 2010 Stefan Lankes, Chair for Operating Systems,
;                               RWTH Aachen University
;
; Licensed under the Apache License, Version 2.0 (the "License");
; you may not use this file except in compliance with the License.
; You may obtain a copy of the License at
;
;     http://www.apache.org/licenses/LICENSE-2.0
;
; Unless required by applicable law or agreed to in writing, software
; distributed under the License is distributed on an "AS IS" BASIS,
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
; See the License for the specific language governing permissions and
; limitations under the License.
;
; This file is part of MetalSVM.

; This is the kernel's entry point for the application processors. We switch to the 
; protected mode and jump to our MetalSVM kernel.

[BITS 16]
SECTION .text
GLOBAL _start
ORG 0x7000
_start:
	cli
	lgdt [gdtr]

	; switch to protected mode by setting PE bit
	mov eax, cr0
	or al, 0x1
	mov cr0, eax

	; far jump to the 32bit code
	jmp dword codesel : _pmstart

[BITS 32]
_pmstart:
	xor eax, eax
	mov ax, datasel
	mov ds, ax
	mov es, ax
	mov fs, ax
	mov gs, ax
	mov ss, ax
	mov esp, 0xDEADBEEF
	push DWORD 0xDEADDEAD
	push DWORD 0x00 ; dummy value
	jmp codesel : 0xDEADC0DE
	jmp $

gdtr:                           ; descritor table
        dw gdt_end-gdt-1        ; limit
        dd gdt                  ; base adresse
gdt:
        dd 0,0                  ; null descriptor
codesel equ $-gdt
        dw 0xFFFF               ; segment size 0..15
        dw 0x0000               ; segment address 0..15
        db 0x00                 ; segment address 16..23
        db 0x9A                 ; access permissions und type
        db 0xCF                 ; additional information and segment size 16...19
        db 0x00                 ; segment address 24..31
datasel equ $-gdt
        dw 0xFFFF               ; segment size 0..15
        dw 0x0000               ; segment address 0..15
        db 0x00                 ; segment address 16..23
        db 0x92                 ; access permissions and type
        db 0xCF                 ; additional informationen and degment size 16...19
        db 0x00                 ; segment address 24..31
gdt_end: