Subversion Repositories Kolibri OS

; KolibriOS bootloader

; bootsector for loading from FAT32 flash (or hard) drive

; intended for use with mtldr_f file in root folder

; this code has been written by diamond in 2005,2006,2007 specially for KolibriOS

; this code is loaded by BIOS to 0000:7C00

	org	0x7C00

	jmp	@f

	nop

	times 57h db 0

;	file 'bt2.dat':3,57h

@@:

	cmp	byte [si], 80h

	jnz	@f

	mov	eax, [si+8]

	mov	[cs:7C1Ch], eax

@@:

	xor	eax, eax

	mov	ds, ax

	mov	ss, ax

	mov	sp, 7C00h

	mov	bp, sp

	mov	[boot_drive], dl

	cld

	sti

	push	800h

	pop	es

	movzx	ebx, word [bp+0Eh]	; reserved_sect

	mov	[fat_start], ebx

	mov	al, byte [bp+10h]	; num_fats

	mul	dword [bp+24h]		; sect_fat

	add	eax, ebx

; cluster 2 begins from sector eax

	movzx	ebx, byte [bp+0Dh]	; sects_per_clust

	add	bx, bx

	sub	eax, ebx

	mov	[data_start], eax

	mov	eax, [bp+2Ch]		; root_cluster

	and	eax, 0FFFFFFFh

fat32_parse_dir:

	xor	bx, bx

	mov	di, bx

	push	eax

	call	read_cluster

	movzx	cx, byte [bp+0Dh]	; sects_per_clust

	shl	cx, 4			; *0x200/0x20

scan_cluster:

	cmp	byte [es:di], 0

	jz	file_not_found

	push	cx di

	mov	cx, 11

	mov	si, mtldr_f

	repz	cmpsb

	pop	di cx

	jz	file_found

	add	di, 20h

	loop	scan_cluster

	pop	eax

	call	next_cluster

	jnc	file_not_found

	jc	fat32_parse_dir

file_found:

	pop	eax

	mov	ax, [es:di+14h]

	and	ax, 0FFFh

	shl	eax, 10h

	mov	ax, [es:di+1Ah]

; eax contains first cluster

@@:

	xor	bx, bx

	push	eax

	call	read_cluster

	mov	ax, es

	movzx	cx, byte [bp+0Dh]

	shl	cx, 5

	add	ax, cx

	mov	es, ax

	pop	eax

	call	next_cluster

	jc	@b

	jmp	0:8000h

file_not_found:

	mov	si, file_not_found_msg

sayerr:

	call	out_string

	jmp	$

read_cluster:

; in: eax = cluster, bx->buffer

	movzx	ecx, byte [bp+0Dh]

	mul	ecx

	add	eax, [data_start]

; read procedure

; in: eax = absolute sector

;     cx = number of sectors

;     es:bx -> buffer

read:

	add	eax, [bp+1Ch]	; hidden sectors

	push	es

read_loop:

	pushad

; allocate disk address packet on the stack

; qword +8: absolute block number

	push	0

	push	0 		; dword +C is high dword

	push	eax		; dword +8 is low dword

; dword +4: buffer address

	push	es		; word +6 is segment

	push	bx		; word +4 is offset

; word +2: number of blocks, limited to 7Fh

	sub	cx, 7Fh

	sbb	ax, ax

	and	ax, cx

	add	ax, 7Fh

	push	ax

	shl	ax, 5

	mov	cx, es

	add	cx, ax

	mov	es, cx

; word +0: size of packet = 10h

	push	10h

; now pair ss:sp contain address of disk address packet

	mov	ax, 4200h

	mov	dl, [boot_drive]

	mov	si, sp

	int	13h

	mov	si, disk_read_err

	jc	sayerr

	popaw

	popad

	add	eax, 7Fh

	sub	cx, 7Fh

	ja	read_loop

	pop	es

	ret

next_cluster:

	push	es

	push	ds

	pop	es

	mov	bx, 7E00h

; sector is 200h bytes long, one entry in FAT occupies 4 bytes

; => 80h entries in sector

	push	eax

	shr	eax, 7		; div 80h

	cmp	eax, [fat_cur_sector]

	jz	@f

	mov	[fat_cur_sector], eax

	add	eax, [fat_start]

	mov	cx, 1

	call	read

@@:

	pop	eax

	and	eax, 7Fh

	mov	eax, [7E00h+eax*4]

	and	eax, 0FFFFFFFh

	cmp	eax, 0FFFFFF7h

	mov	si, bad_cluster

	jz	sayerr

	pop	es

	ret

out_string:

	lodsb

	test	al, al

	jz	.xxx

	mov	ah, 0Eh

	mov	bx, 7

	int	10h

	jmp	out_string

.xxx:	ret

file_not_found_msg	db	'Cannot find file '

mtldr_f			db	'MTLD_F32   '

			db	13,10,0

disk_read_err		db	'Disk read error',13,10,0

bad_cluster		db	'Bad cluster',13,10,0

fat_cur_sector	dd	-1

	times (7DFEh - $) db 0

	db	55h, 0AAh

virtual at 7A00h

fat_start	dd	?

data_start	dd	?

boot_drive	db	?

end virtual