OSDev.org

Code: Select all

%define BODY_SEC_LENGTH ((BodyEnd - Body) / 512) + 1
%include "kernelSize.inc"

BITS 16
ORG 0x7C00

Boot:
	XOR	AX, AX           ;Loads the segment registers
	MOV	DS, AX
	MOV	ES, AX
	MOV	SS, AX
	MOV	SP, 7C00h
	
	MOV	AX, 200h + BODY_SEC_LENGTH
	MOV	CX, 2
	XOR	DX, DX
	MOV BX, 7E00h
	INT	13h              ;Read the bootloader from sector 2
	
	JMP	0000h:7E00h ;Jump to the bootloader code
	
	times (510 - ($ - Boot)) DB 0  ;filler
	DW	0AA55h                     ;bootloader magic number

Body:
	PUSH	WORD MsgWelcome
	CALL	Print
	
	CLI                    ;disable interrupts
	IN	AL, 70h
	OR	AL, 80h
	OUT	70h, AL   ;disable NMI

	CALL	A20Enable  ;enable A20 line

	PUSH	WORD MsgGDT
	CALL	Print
	LGDT	[GDTInfo]  ;loads GDT

	PUSH	WORD MsgPE
	CALL	Print

	MOV EAX, CR0
	OR	AL, 1
	MOV	CR0, EAX          ;switch to PM

	JMP DWORD 8:Main32    ;Jump to PM code

A20Enable:
	PUSH	AX
	
	PUSH	WORD MsgA20
	CALL	Print

	CALL	KbdWaitOutput

	MOV	AL, 0D0h
	OUT	64h, AL
	CALL	KbdWaitInput

	XOR	AX, AX
	IN	AL, 60h
	OR	AL, 2

        PUSH	AX
	CALL	KbdWaitOutput
	MOV	AL, 0D1h
	OUT	64h, AL
	
	CALL	KbdWaitOutput
	
	POP	AX
	OUT	60h, AL
	
	POP	AX
	RET

KbdWaitOutput:
	IN	AL, 64h
	TEST	AL, 2
	JNZ SHORT KbdWaitOutput
	RET

KbdWaitInput:
	IN	AL, 64h
	TEST	AL, 1
	JZ SHORT KbdWaitInput
	RET

Print:
%define	Message BP + 4
	PUSH	BP
	MOV	BP, SP
	
	PUSH	AX
	PUSH	BX
	PUSH	SI
	
	MOV	SI, WORD [Message]
	MOV	AH, 0Eh
	XOR	BX, BX
NextChar:
	LODSB
	TEST	AL, AL
	JZ	SHORT Done
	INT	10h
	JMP	SHORT NextChar

Done:
	POP	SI
	POP	BX
	POP	AX
	
	MOV	SP, BP
	POP	BP
	
	RET	2

%undef	Message

BITS 32
Main32:
        MOV	AX, 10h      ;Loads segment registers
	MOV	DS, AX
        MOV	ES, AX
	MOV	SS, AX

ReadFloppy:
	MOV	SI, KRNL_SIZE
	XOR	BX, BX
        MOV	AX, 1000h              :HERE IS THE PROBLEM
        MOV	ES, AX                   ;WHILE MOVING AX TO ES
	MOV	CX, 3
	XOR	DX, DX

Again:
	PUSH	AX
	PUSH	BX
	MOV	AX, 0E00h + '.'  
	MOV	BX, 7
	INT	10h
	POP	BX
	POP	AX
	
	MOV	AX, 0201h
	INT	13h                    ;Read the kernel from the floppy
	JC	SHORT Error

	MOV	AX, ES
	ADD	AX, 32
	MOV	ES, AX

	DEC	SI
	JZ	SHORT ReadOK

	INC	CX
	CMP	CL, 18
	JBE	SHORT Again
	MOV	CL, 1
	INC	DH
	CMP	DH, 2
	JNE	SHORT Again
	MOV	DH, 0
	INC	CH
	JMP	SHORT Again

Error:
	MOV	AX, 0E00h + 'e'
	MOV	BX, 7
	INT 10h
	XOR	AX, AX
	INT	16h
	INT	19h

ReadOK:
	MOV	EDX, 3F2h
	MOV	AL, 0Ch
	OUT	DX, AL          ;Shut down the floppy motor

        MOV     AX, 1000h    ;Start the kernel
        JMP       AX

        JMP	$
	
	CLI
	HLT

GDT:
	DD	0, 0

	DW  0FFFFh
	DW  0
	DB  0
	DB  9Ah
	DB  0CFh
	DB  0

	DW	0FFFFh
	DW  0
	DB  0
	DB  92h
	DB  0CFh
	DB  0
GDTEnd:

GDTInfo:
	DW	GDTEnd - GDT - 1
	DD	GDT

FloppyOff:
	MOV	DX, 3F2h
	MOV	AL, 0Ch
	OUT	DX, AL
	RET

MsgWelcome:
	times 80 DB '-'
	DB "Boot process", 13, 10
	times 80 DB '-'
	
	DB 0

MsgA20		DB "A20...", 10, 13, 0
MsgGDT		DB "GDT...", 10, 13, 0
MsgPE		DB "PM...", 13, 10, 0
	
BodyEnd:
length EQU ((((BodyEnd-Boot) / 512) + 1) * 512)
length2 EQU (BodyEnd-Boot)
times (length - length2) DB 0

Code: Select all

JMP    DWORD 8h:Main32

Code: Select all

objdump -d my_kernel.bin

Code: Select all

00028963558i[CPU0 ] CS.d_b = 32 bit
00028963558i[CPU0 ] SS.d_b = 16 bit

Code: Select all

00028963558i[CPU0 ] | SEG sltr(index|ti|rpl) base limit G D 
00028963558i[CPU0 ] | CS:0008( 0001| 0| 0) 00000000 000fffff 1 1
00028963558i[CPU0 ] | DS:0010( 0002| 0| 0) 00000000 000fffff 1 1
00028963558i[CPU0 ] | SS:0000( 0005| 0| 0) 00000000 0000ffff 0 0
00028963558i[CPU0 ] | ES:0000( 0005| 0| 0) 00000000 0000ffff 0 0
00028963558i[CPU0 ] | FS:0000( 0005| 0| 0) 00000000 0000ffff 0 0
00028963558i[CPU0 ] | GS:0000( 0005| 0| 0) 00000000 0000ffff 0 0 

Code: Select all

CLI                    ;disable interrupts 
IN   AL, 70h 
OR   AL, 80h 
OUT   70h, AL   ;disable NMI