Subversion Repositories Kolibri OS

Rev

Rev 2785 | Go to most recent revision | Details | Last modification | View Log | RSS feed

Rev Author Line No. Line
2783 clevermous 1 
; KolibriOS bootloader
2 
; bootsector for loading from FAT32 flash (or hard) drive
3 
; intended for use with mtldr_f file in root folder
4 
; this code has been written by diamond in 2005,2006,2007 specially for KolibriOS
5 
 
6 
; this code is loaded by BIOS to 0000:7C00
7 
	org	0x7C00
8 
	jmp	@f
9 
	nop
10 
;	times 57h db 0
11 
	file 'bt2.dat':3,57h
12 
@@:
13 
	xor	eax, eax
14 
	mov	ds, ax
15 
	mov	ss, ax
16 
	mov	sp, 7C00h
17 
	mov	[boot_drive], dl
18 
	cld
19 
	sti
20 
	push	800h
21 
	pop	es
22 
	movzx	ebx, word [7C0Eh]	; reserved_sect
23 
	mov	[fat_start], ebx
24 
	mov	al, byte [7C10h]	; num_fats
25 
	mul	dword [7C24h]		; sect_fat
26 
	add	eax, ebx
27 
; cluster 2 begins from sector eax
28 
	movzx	ebx, byte [7C0Dh]	; sects_per_clust
29 
	add	bx, bx
30 
	sub	eax, ebx
31 
	mov	[data_start], eax
32 
	mov	eax, [7C2Ch]		; root_cluster
33 
	and	eax, 0FFFFFFFh
34 
fat32_parse_dir:
35 
	xor	bx, bx
36 
	mov	di, bx
37 
	push	eax
38 
	call	read_cluster
39 
	movzx	cx, byte [7C0Dh]	; sects_per_clust
40 
	shl	cx, 4			; *0x200/0x20
41 
scan_cluster:
42 
	cmp	byte [es:di], 0
43 
	jz	file_not_found
44 
	push	cx di
45 
	mov	cx, 11
46 
	mov	si, mtldr_f
47 
	repz	cmpsb
48 
	pop	di cx
49 
	jz	file_found
50 
	add	di, 20h
51 
	loop	scan_cluster
52 
	pop	eax
53 
	call	next_cluster
54 
	jnc	file_not_found
55 
	jc	fat32_parse_dir
56 
file_found:
57 
	pop	eax
58 
	mov	ax, [es:di+14h]
59 
	and	ax, 0FFFh
60 
	shl	eax, 10h
61 
	mov	ax, [es:di+1Ah]
62 
; eax contains first cluster
63 
@@:
64 
	xor	bx, bx
65 
	push	eax
66 
	call	read_cluster
67 
	mov	ax, es
68 
	movzx	cx, byte [7C0Dh]
69 
	shl	cx, 5
70 
	add	ax, cx
71 
	mov	es, ax
72 
	pop	eax
73 
	call	next_cluster
74 
	jc	@b
75 
	jmp	0:8000h
76 
 
77 
file_not_found:
78 
	mov	si, file_not_found_msg
79 
sayerr:
80 
	call	out_string
81 
	jmp	$
82 
 
83 
read_cluster:
84 
; in: eax = cluster, bx->buffer
85 
	movzx	ecx, byte [7C0Dh]
86 
	mul	ecx
87 
	add	eax, [data_start]
88 
 
89 
; read procedure
90 
; in: eax = absolute sector
91 
;     cx = number of sectors
92 
;     es:bx -> buffer
93 
read:
94 
	add	eax, [7C1Ch]	; hidden sectors
95 
	push	es
96 
read_loop:
97 
	pushad
98 
; allocate disk address packet on the stack
99 
; qword +8: absolute block number
100 
	push	0
101 
	push	0 		; dword +C is high dword
102 
	push	eax		; dword +8 is low dword
103 
; dword +4: buffer address
104 
	push	es		; word +6 is segment
105 
	push	bx		; word +4 is offset
106 
; word +2: number of blocks, limited to 7Fh
107 
	sub	cx, 7Fh
108 
	sbb	ax, ax
109 
	and	ax, cx
110 
	add	ax, 7Fh
111 
	push	ax
112 
	shl	ax, 5
113 
	mov	cx, es
114 
	add	cx, ax
115 
	mov	es, cx
116 
; word +0: size of packet = 10h
117 
	push	10h
118 
; now pair ss:sp contain address of disk address packet
119 
	mov	ax, 4200h
120 
	mov	dl, [boot_drive]
121 
	mov	si, sp
122 
	int	13h
123 
	mov	si, disk_read_err
124 
	jc	sayerr
125 
	popaw
126 
	popad
127 
	add	eax, 7Fh
128 
	sub	cx, 7Fh
129 
	ja	read_loop
130 
	pop	es
131 
	ret
132 
 
133 
next_cluster:
134 
	push	es
135 
	push	ds
136 
	pop	es
137 
	mov	bx, 7E00h
138 
; sector is 200h bytes long, one entry in FAT occupies 4 bytes
139 
; => 80h entries in sector
140 
	push	eax
141 
	shr	eax, 7		; div 80h
142 
	cmp	eax, [fat_cur_sector]
143 
	jz	@f
144 
	mov	[fat_cur_sector], eax
145 
	add	eax, [fat_start]
146 
	mov	cx, 1
147 
	call	read
148 
@@:
149 
	pop	eax
150 
	and	eax, 7Fh
151 
	mov	eax, [7E00h+eax*4]
152 
	and	eax, 0FFFFFFFh
153 
	cmp	eax, 0FFFFFF7h
154 
	mov	si, bad_cluster
155 
	jz	sayerr
156 
	pop	es
157 
	ret
158 
 
159 
out_string:
160 
	lodsb
161 
	test	al, al
162 
	jz	.xxx
163 
	mov	ah, 0Eh
164 
	mov	bx, 7
165 
	int	10h
166 
	jmp	out_string
167 
.xxx:	ret
168 
 
169 
file_not_found_msg	db	'Cannot find file '
170 
mtldr_f			db	'MTLD_F32   '
171 
			db	13,10,0
172 
disk_read_err		db	'Disk read error',13,10,0
173 
bad_cluster		db	'Bad cluster',13,10,0
174 
fat_cur_sector	dd	-1
175 
 
176 
	times (7DFEh - $) db 0
177 
	db	55h, 0AAh
178 
 
179 
virtual at 7A00h
180 
fat_start	dd	?
181 
data_start	dd	?
182 
boot_drive	db	?
183 
end virtual