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;; print a message to the screen
;; in SI = string to print (NUL-terminated)
;; in DL = color attribute to be used
;; DI, ES = destroyed
putmsg:
	mov	ax,	0xb800
	mov	es,	ax
	xor	di,	di
	mov	cx,	80*25*2
	mov	al,	0
	rep	stosb			; clear the screen
	xor	di,	di

	.loop:
	lodsb
	test	al,	al
	jz	.ret
	mov	ah,	dl
	stosw
	jmp	.loop

	.ret:
	ret

;; STRINGS
str_loading db 'Loading stage2.bin', 0
str_config_fail db 'Nextep loader stage1.bin configuration invalid', 0
str_passing db 'Passing control to stage2.bin', 0

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mov si, str_passing
mov dl, 0x02
call putmsg

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;; print a message to the screen
;; in SI = string to print (NUL-terminated)
;; in DL = color attribute to be used
;; DI, ES = destroyed
putmsg:
	mov	ax,	0xb800
	mov	es,	ax
	xor	di,	di
	mov	cx,	80*25
	;mov	ax,	0720h		;would be better
	xor	ax,	ax
	rep	stosw			; clear the screen
	xor	di,	di
	mov	ah,	dl

;;assuming you don't want to print empty string
	.loop:
	lodsb
	stosw
	or	al,	al
	jnz	.loop
	ret

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;; Nextep loader stage 1
;; This file must be put in the boot sector of your boot disk
;; it will load the stage2.bin file, located at the first few
;; sectors of the boot disk.

org 0x7C00
bits 16

ATTR_GREEN	equ 0x02
ATTR_RED	equ 0x04
ATTR_WHITE	equ 0x07

;; make sure the header is not executed
;; (jump over it)
db 0xEB
db ConfigHeader.end-ConfigHeader

ConfigHeader:
	.bootdisk	db 0x00			;; 00h=fd0, 01h=fd1, 80h=hd0, 81h=hd1		[offset 2]
	.stage2size	dw 3			;; size of the stage2.bin file (in sectors)	[offset 3]
	.width		dw 720			;; preferred screen width			[offset 5]
	.height		dw 480			;; preferred screen height			[offset 7]
	.end:

;; set up the registers correctly
mov	ax,	0
mov	ds,	ax
mov	ss,	ax
jmp	0:_start
_start:

;; reset the correct video mode (some BIOSes set up a graphics mode to start with)
mov	ax,	2
int	10h

;; set up a stack
mov	sp,	0x7CFF

;; Make sure everything is OK
mov	ax,	[ConfigHeader.stage2size]
test	ax,	ax
jnz	ok0

;; if not OK, print an error message
mov	si,	str_config_fail
mov	dl,	ATTR_RED
call	putmsg
cli
hlt

;; Main loading routine
ok0:
mov	si,	str_loading
mov	dl,	ATTR_WHITE
call	putmsg

loadloop:
mov	ax,	0x7E0
mov	es,	ax
mov	ah,	0x02
mov	al,	[ConfigHeader.stage2size]
mov	cx,	2
mov	dh,	0
mov	dl,	[ConfigHeader.bootdisk]
mov	bx,	0
int	13h
jc	loadloop				; if failed, retry

;; tell the user we are about to pass control to stage2.bin
mov	si,	str_passing
mov	dl,	ATTR_GREEN
call	putmsg

;; finally, run stage2.bin!
jmp	0x7E0:0

;; print a message to the screen
;; in SI = string to print (NUL-terminated)
;; in DL = color attribute to be used
;; DI, ES = destroyed
putmsg:
	mov	ax,	0xb800
	mov	es,	ax
	xor	di,	di
	mov	cx,	80*25*2
	mov	al,	0
	rep	stosb			; clear the screen
	xor	di,	di

	.loop:
	lodsb
	test	al,	al
	jz	.ret
	mov	ah,	dl
	stosw
	jmp	.loop

	.ret:
	ret

;; STRINGS
str_loading db 'Loading stage2.bin', 0
str_config_fail db 'Nextep loader stage1.bin configuration invalid', 0
str_passing db 'Passing control to stage2.bin', 0

times 510 - ($ - $$) db 0
db 0x55, 0xAA

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mov   ax,   2
int   10h