borbular/bootloader.asm at main · okforth/borbular · GitHub

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BITS 16
org 0x7c00

	jmp	start

	; FAT headers stops at 3e
	times 0x3e - ( $ - $$ ) db 0

bootdrive: db 0

start:
	; store bootdrive for later
	mov	[bootdrive], dl

	; clear direction flag
	cld

	; set up hardware stack
	xor	ax, ax
	mov	es, ax
	mov	ss, ax
	mov	ds, ax
	mov	sp, ax

	; load kernel
	mov	ah, 0x02
	mov	al, 59		; sector count
	mov	ch, 0		; cylinder
	mov	cl, 2		; sector
	mov	dh, 0		; head
				; dl = boot drive
	mov	bx, 0x0500	; destination address
	int	0x13

	; load source
	mov	ah, 0x02
	mov	al, 3		; sector count
	mov	ch, 0		; cylinder
	mov	cl, 61		; sector
	mov	dh, 0		; head
				; dl = boot drive
	mov	bx, 0x7e00	; destination address
	int	0x13

	mov	ah, 0x02
	mov	al, 60		; sector count
	mov	ch, 0		; cylinder
	mov	cl, 1		; sector
	mov	dh, 1		; head
				; dl = boot drive
	add	bx, 512*3	; destination address
	int	0x13

	; clear screen
	mov	ax, 0x0003	; 80x25 16 color text
	int	0x10

	jmp	0:0x0500	; goto: kernel

	; magic numbers
	times 510 - ( $ - $$ ) db 0
	db	0x55, 0xaa