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1 | #------------------------------------------------------------------------------ | |
2 | #* | |
3 | #* Copyright 2006 - 2007, Intel Corporation | |
4 | #* All rights reserved. This program and the accompanying materials | |
5 | #* are licensed and made available under the terms and conditions of the BSD License | |
6 | #* which accompanies this distribution. The full text of the license may be found at | |
7 | #* http://opensource.org/licenses/bsd-license.php | |
8 | #* | |
9 | #* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, | |
10 | #* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. | |
11 | #* | |
12 | #* Mbr.asm | |
13 | #* | |
14 | #* Abstract: | |
15 | #* | |
16 | #------------------------------------------------------------------------------ | |
17 | ||
18 | .equ BLOCK_SIZE, 0x0200 | |
19 | .equ BLOCK_MASK, 0x01ff | |
20 | .equ BLOCK_SHIFT, 9 | |
21 | ||
22 | # **************************************************************************** | |
23 | # Code loaded by BIOS at 0x0000:0x7C00 | |
24 | # **************************************************************************** | |
25 | ||
26 | .org 0x0 | |
27 | ||
28 | .global _start\r | |
29 | _start: | |
30 | ||
31 | # **************************************************************************** | |
32 | # Start Print | |
33 | # **************************************************************************** | |
34 | ||
35 | movw $0xb800, %ax | |
36 | movw %ax, %es | |
37 | movw $0x7c0, %ax | |
38 | movw %ax, %ds | |
39 | leaw %cs:StartString, %si | |
40 | movw $10, %cx | |
41 | movw $160, %di | |
42 | rep | |
43 | movsw | |
44 | ||
45 | # **************************************************************************** | |
46 | # Print over | |
47 | # **************************************************************************** | |
48 | ||
49 | # **************************************************************************** | |
50 | # Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600 | |
51 | # **************************************************************************** | |
52 | xorw %ax, %ax # AX = 0x0000 | |
53 | movw $0x7c00, %bx # BX = 0x7C00 | |
54 | movw $0x600, %bp # BP = 0x0600 | |
55 | movw RelocatedStart, %si # SI = Offset(RelocatedStart) | |
56 | movw $0x200, %cx # CX = 0x0200 | |
57 | subw %si, %cx # CS = 0x0200 - Offset(RelocatedStart) | |
58 | leaw (%bp,%si,), %di # DI = 0x0600 + Offset(RelocatedStart) | |
59 | leaw (%bx,%si,), %si # BX = 0x7C00 + Offset(RelocatedStart) | |
60 | movw %ax, %ss # SS = 0x0000 | |
61 | movw %bx, %sp # SP = 0x7C00 | |
62 | movw %ax, %es # ES = 0x0000 | |
63 | movw %ax, %ds # DS = 0x0000 | |
64 | pushw %ax # PUSH 0x0000 | |
65 | pushw %di # PUSH 0x0600 + Offset(RelocatedStart) | |
66 | cld # Clear the direction flag | |
67 | rep | |
68 | movsb # Copy 0x0200 bytes from 0x7C00 to 0x0600 | |
69 | retl # JMP 0x0000:0x0600 + Offset(RelocatedStart) | |
70 | ||
71 | # **************************************************************************** | |
72 | # Code relocated to 0x0000:0x0600 | |
73 | # **************************************************************************** | |
74 | ||
75 | RelocatedStart: | |
76 | # **************************************************************************** | |
77 | # Get Driver Parameters to 0x0000:0x7BFC | |
78 | # **************************************************************************** | |
79 | ||
80 | xorw %ax, %ax # AX = 0 | |
81 | movw %ax, %ss # SS = 0 | |
82 | addw $0x1000, %ax | |
83 | movw %ax, %ds | |
84 | ||
85 | movw $0x7c00, %sp # SP = 0x7c00 | |
86 | movw %sp, %bp # BP = 0x7c00 | |
87 | ||
88 | movb $8, %ah # AH = 8 - Get Drive Parameters Function | |
89 | movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL | |
90 | int $0x13 # Get Drive Parameters | |
91 | xorw %ax, %ax # AX = 0 | |
92 | movb %dh, %al # AL = DH | |
93 | incb %al # MaxHead = AL + 1 | |
94 | pushw %ax # 0000:7bfe = MaxHead | |
95 | movb %cl, %al # AL = CL | |
96 | andb $0x3f, %al # MaxSector = AL & 0x3f | |
97 | pushw %ax # 0000:7bfc = MaxSector | |
98 | ||
99 | # **************************************************************************** | |
100 | # Read Target DBR from hard disk to 0x0000:0x7C00 | |
101 | # **************************************************************************** | |
102 | ||
103 | xorw %ax, %ax | |
104 | movb MbrPartitionIndicator(%bp), %al # AX = MbrPartitionIndex | |
105 | cmpb $0xff, %al # 0xFF means do legacy MBR boot | |
106 | jnz EfiDbr | |
107 | LegacyMbr: | |
108 | movl $0x0000600, %eax # Assume LegacyMBR is backuped in Sector 6 | |
109 | jmp StartReadTo7C00 # EAX = Header/Sector/Tracker/Zero | |
110 | ||
111 | EfiDbr: | |
112 | cmpb $4, %al # MbrPartitionIndex should < 4 | |
113 | jae BadDbr | |
114 | shlw $4, %ax # AX = MBREntrySize * Index | |
115 | addw $0x1be, %ax # AX = MBREntryOffset | |
116 | movw %ax, %di # DI = MBREntryOffset | |
117 | ||
118 | # Here we don't use the C/H/S information provided by Partition table | |
119 | # but calculate C/H/S from LBA ourselves | |
120 | # Ci: Cylinder number | |
121 | # Hi: Header number | |
122 | # Si: Sector number | |
123 | movl %es:8(%bp,%di,), %eax # Start LBA | |
124 | movl %eax, %edx | |
125 | shrl $16, %edx # DX:AX = Start LBA | |
126 | # = Ci * (H * S) + Hi * S + (Si - 1) | |
127 | ||
128 | # Calculate C/H/S according to LBA | |
129 | movw $0x7bfa, %bp | |
130 | divw 2(%bp) # AX = Hi + H*Ci | |
131 | # DX = Si - 1 | |
132 | incw %dx # DX = Si | |
133 | pushw %dx # 0000:7bfa = Si <---- | |
134 | xorw %dx, %dx # DX:AX = Hi + H*Ci | |
135 | divw 4(%bp) # AX = Ci <---- | |
136 | # DX = Hi <---- | |
137 | ||
138 | StartReadTo7C00: | |
139 | ||
140 | movb (%bp), %cl # Si | |
141 | movb %al, %ch # Ci[0-7] | |
142 | orb %ah, %cl # Ci[8,9] | |
143 | movw $0x7c00, %bx # ES:BX = 0000:7C00h | |
144 | movb $0x2, %ah # Function 02h | |
145 | movb $1, %al # 1 Sector | |
146 | movb %dl, %dh # Hi | |
147 | movw $0x600, %bp | |
148 | movb PhysicalDrive(%bp), %dl # Drive number | |
149 | int $0x13 | |
150 | jc BadDbr | |
151 | ||
152 | ||
153 | ||
154 | # **************************************************************************** | |
155 | # Transfer control to BootSector - Jump to 0x0000:0x7C00 | |
156 | # **************************************************************************** | |
157 | xorw %ax, %ax | |
158 | pushw %ax # PUSH 0x0000 - Segment | |
159 | movw $0x7c00, %di | |
160 | pushw %di # PUSH 0x7C00 - Offset | |
161 | retl # JMP 0x0000:0x7C00 | |
162 | ||
163 | # **************************************************************************** | |
164 | # ERROR Condition: | |
165 | # **************************************************************************** | |
166 | ||
167 | BadDbr: | |
168 | pushw %ax | |
169 | movw $0xb800, %ax | |
170 | movw %ax, %es | |
171 | movw $0x60, %ax | |
172 | movw %ax, %ds | |
173 | leaw %cs:ErrorString, %si | |
174 | movw $320, %di | |
175 | popw %ax | |
176 | call A2C | |
177 | movb %ah, 16(%si) | |
178 | movb %al, 18(%si) | |
179 | movw $10, %cx | |
180 | rep | |
181 | movsw | |
182 | Halt: | |
183 | jmp Halt | |
184 | ||
185 | StartString: | |
186 | .byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c | |
187 | ErrorString: | |
188 | .byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, ':', 0x0c, '?', 0x0c, '?', 0x0c | |
189 | ||
190 | # **************************************************************************** | |
191 | # A2C - convert Ascii code stored in AH to character stored in AX | |
192 | # **************************************************************************** | |
193 | A2C: | |
194 | movb %ah, %al | |
195 | shrb $4, %ah | |
196 | andb $0xF, %al | |
197 | addb '0', %ah | |
198 | addb '0', %al | |
199 | ||
200 | cmpb '9', %ah | |
201 | jle A2C_L1 | |
202 | addb $7, %ah | |
203 | A2C_L1: | |
204 | ||
205 | cmpb '9', %al | |
206 | jle A2C_L2 | |
207 | addb $7, %al | |
208 | A2C_L2: | |
209 | ret | |
210 | ||
211 | ||
212 | # **************************************************************************** | |
213 | # PhysicalDrive - Used to indicate which disk to be boot | |
214 | # Can be patched by tool | |
215 | # **************************************************************************** | |
216 | .org 0x01B6 | |
217 | PhysicalDrive: .byte 0x80 | |
218 | ||
219 | # **************************************************************************** | |
220 | # MbrPartitionIndicator - Used to indicate which MBR partition to be boot | |
221 | # Can be patched by tool | |
222 | # OxFF means boot to legacy MBR. (LBA OFFSET 6) | |
223 | # **************************************************************************** | |
224 | .org 0x01B7 | |
225 | MbrPartitionIndicator: .byte 0 | |
226 | ||
227 | # **************************************************************************** | |
228 | # Unique MBR signature | |
229 | # **************************************************************************** | |
230 | .org 0x01B8 | |
231 | .ascii "DUET" | |
232 | ||
233 | # **************************************************************************** | |
234 | # Unknown | |
235 | # **************************************************************************** | |
236 | .org 0x01BC | |
237 | .word 0 | |
238 | ||
239 | # **************************************************************************** | |
240 | # MBR Entry - To be patched | |
241 | # **************************************************************************** | |
242 | .org 0x01BE | |
243 | .long 0,0,0,0 | |
244 | .org 0x01CE | |
245 | .long 0,0,0,0 | |
246 | .org 0x01DE | |
247 | .long 0,0,0,0 | |
248 | .org 0x01EE | |
249 | .long 0,0,0,0 | |
250 | ||
251 | # **************************************************************************** | |
252 | # Sector Signature | |
253 | # **************************************************************************** | |
254 | ||
255 | .org 0x01FE | |
256 | SectorSignature: | |
257 | .word 0xaa55 # Boot Sector Signature | |
258 | ||
259 | ||
260 |