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;;;
;; <header id="source/system/start.asm">
;;   <description>Enters 32-bit protected mode, then the C
;;                kernel.</description>
;;   <copyright>Copyright (C) 2007, Griffinsoft Corporation</copyright>
;;   <website>http://www.griffinsoft.net/</website>
;;   <notes>
;;     <!--None-->
;;   </notes>
;; </header>
;;;

[BITS 16]
[GLOBAL start]

;; Jump directly to Start
jmp Start

;;;
;; <function id="Start">
;;   <description>Enters protected mode and sets up the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
Start:
    xor ebx, ebx
    mov bx, cs
    shl ebx, 4
    mov eax, ebx
    lea eax, [ebx]
    mov [GDT2 + 2], ax
    mov [GDT3 + 2], ax
    shr eax, 16
    mov [GDT2 + 4], al
    mov [GDT3 + 4], al
    mov [GDT2 + 7], ah
    mov [GDT3 + 7], ah
    lea eax, [ebx + GDT]
    mov [GDTPointer + 2], eax
    push dword 0
    popfd
    o32 lgdt [GDTPointer]
    mov eax, cr0
    or al, 1
    mov cr0, eax
    jmp codeSelector:ProtectedMode

[BITS 32]

;;;
;; <function id="ProtectedMode">
;;   <description>Goes to the C kernel.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
ProtectedMode:
    mov ax, dataSelector
    mov ds, eax
    mov ss, eax
    nop
    mov es, eax
    mov fs, eax
    mov gs, eax
    xor eax, eax
    mov ax, sp
    mov esp, eax
[EXTERN _Kernel]
    call _Kernel
    jmp $

;;;
;; <function id="GDT">
;;   <description>Part of the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
GDT:
    dw 0
    dw 0
    db 0
    db 0
    db 0
    db 0

;;;
;; <function id="linearSelector">
;;   <description>Linear segment selector.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
linearSelector equ $-GDT
    dw 0xFFFF
    dw 0
    db 0
    db 0x92
    db 0xCF
    db 0

;;;
;; <function id="codeSelector">
;;   <description>Code segment selector.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
codeSelector equ $-GDT

;;;
;; <function id="GDT2">
;;   <description>Part of the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
GDT2:
    dw 0xFFFF
    dw 0
    db 0
    db 0x9A
    db 0xCF
    db 0

;;;
;; <function id="dataSelector">
;;   <description>Data segment selector.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
dataSelector equ $-GDT

;;;
;; <function id="GDT3">
;;   <description>Part of the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
GDT3:
    dw 0xFFFF
    dw 0
    db 0
    db 0x92
    db 0xCF
    db 0

;;;
;; <function id="GDTEnd">
;;   <description>Part of the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
GDTEnd:

;;;
;; <function id="GDTPointer">
;;   <description>Part of the GDT.</description>
;;   <parameters>
;;     <!--None-->
;;   </parameters>
;; </function>
;;;
GDTPointer:
    dw GDTEnd - GDT - 1
    dd GDT