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;===============================================================
;
;	            ISOSYS v1.0 in isosys.asm
;
; Program for booting OS32 and OS32-based systems from CD/DVDs
; using the ElTorito boot standard.
;
; By Omar, 2014
;
; ===============================================================

; set up bios...
bits 16
org 0x7c00

; beginning of sector 1, byte 0:

; jump over functions block
jmp Start

;
; Print()
;		prints a string to standard output
; AL = 0 : terminate
;

Print:
	lodsb				; grab a byte from SI and place it in AL
	cmp al, 0			; is AL = 0?
	jc PrintDone			; yep, we're done so return
	mov ah, 0eh
	int 0x10			; nope, print the character
	jmp Print			; loop until no more characters to be printed
PrintDone:
	ret				; return to wherever we were!

;
; Start()
;		bootloader entry point
;

Start:
	mov si, creditmsg
	call Print			; print the first message
	mov dh, 1			; read 1 sector

.ReadSector:
	cli				; disable interrupts
	push dx				; push this stack value
	sti				; re-enable interrupts

	mov ax, 0x1000			; read sector into address 0x1000
	xor bx, bx			; read sector into offset 0x0
	mov ah, 0x02			; read sector function
	mov al, dh			; read 1 sector
	mov ch, 0x0			; must be 0x0 to read sector
	mov dh, 0			; reading head 0
	mov cl, 0x02			; start reading from sector 2 to load the second stage

	mov [CDDriveNumber], dl		; store our drive number is variable CDDriveNumber
	cli				; disable interrupts
	pusha				; save the stack
	sti				; enable interrupts

	int 0x13			; INT 13h
	jc Error			; handle error because Carry Flag is set

	pop dx				; Restore DX

.ExecuteSector:
	; now that our sector was loaded into address 0x1000:0x0, let's execute it!
	jmp 0x1000:0x0			; jump to execute the sector
;
; Error()
;		handles errors when carry is set
;

Error:
	mov si, errmsg
	call Print			; print an error message

	cli				; disable interrupts to prevent problems
	hlt				; halt the system... :(

; data section

creditmsg db "ISOSYS v1.0 by Omar Mohammad, Init...", 0
errmsg db "Cannot load the second stage. (File not found maybe?)", 0
CDDriveNumber db 0

times 2048 - ($-$$) db 0		; fill in 2048 bytes with zeroes

; end of sector 1! :D Any more code here would take bytes 2048 and 2049 but we don't need that...

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bits 16
org 0x1000

Main:
	xor bx, bx
	mov ah, 0eh
	mov al, 'A'
	int 0x10

	cli
	hlt

times 2048 - ($-$$) db 0

Code: Select all

cmp al, 0
jc PrintDone