1#------------------------------------------------------------------------------ 2#* 3#* Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR> 4#* 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 .code16 19 20.equ BLOCK_SIZE, 0x0200 21.equ BLOCK_MASK, 0x01ff 22.equ BLOCK_SHIFT, 9 23 24# **************************************************************************** 25# Code loaded by BIOS at 0x0000:0x7C00 26# **************************************************************************** 27 28.org 0x0 29 30.global _start 31_start: 32 33# **************************************************************************** 34# Start Print 35# **************************************************************************** 36 37 movw $0xb800, %ax 38 movw %ax, %es 39 movw $0x7c0, %ax 40 movw %ax, %ds 41 leaw %cs:StartString, %si 42 movw $10, %cx 43 movw $160, %di 44 rep 45 movsw 46 47# **************************************************************************** 48# Print over 49# **************************************************************************** 50 51# **************************************************************************** 52# Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600 53# **************************************************************************** 54 xorw %ax, %ax # AX = 0x0000 55 movw $0x7c00, %bx # BX = 0x7C00 56 movw $0x600, %bp # BP = 0x0600 57 movw $RelocatedStart, %si # SI = Offset(RelocatedStart) 58 movw $0x200, %cx # CX = 0x0200 59 subw %si, %cx # CS = 0x0200 - Offset(RelocatedStart) 60 leaw (%bp,%si,), %di # DI = 0x0600 + Offset(RelocatedStart) 61 leaw (%bx,%si,), %si # BX = 0x7C00 + Offset(RelocatedStart) 62 movw %ax, %ss # SS = 0x0000 63 movw %bx, %sp # SP = 0x7C00 64 movw %ax, %es # ES = 0x0000 65 movw %ax, %ds # DS = 0x0000 66 pushw %ax # PUSH 0x0000 67 pushw %di # PUSH 0x0600 + Offset(RelocatedStart) 68 cld # Clear the direction flag 69 rep 70 movsb # Copy 0x0200 bytes from 0x7C00 to 0x0600 71 retl # JMP 0x0000:0x0600 + Offset(RelocatedStart) 72 73# **************************************************************************** 74# Code relocated to 0x0000:0x0600 75# **************************************************************************** 76 77RelocatedStart: 78# **************************************************************************** 79# Get Driver Parameters to 0x0000:0x7BFC 80# **************************************************************************** 81 82 xorw %ax, %ax # AX = 0 83 movw %ax, %ss # SS = 0 84 addw $0x1000, %ax 85 movw %ax, %ds 86 87 movw $0x7c00, %sp # SP = 0x7c00 88 movw %sp, %bp # BP = 0x7c00 89 90 movb $8, %ah # AH = 8 - Get Drive Parameters Function 91 movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL 92 int $0x13 # Get Drive Parameters 93 xorw %ax, %ax # AX = 0 94 movb %dh, %al # AL = DH 95 incb %al # MaxHead = AL + 1 96 pushw %ax # 0000:7bfe = MaxHead 97 movb %cl, %al # AL = CL 98 andb $0x3f, %al # MaxSector = AL & 0x3f 99 pushw %ax # 0000:7bfc = MaxSector 100 101# **************************************************************************** 102# Read Target DBR from hard disk to 0x0000:0x7C00 103# **************************************************************************** 104 105 xorw %ax, %ax 106 movb MbrPartitionIndicator(%bp), %al # AX = MbrPartitionIndex 107 cmpb $0xff, %al # 0xFF means do legacy MBR boot 108 jnz EfiDbr 109LegacyMbr: 110 movl $0x0000600, %eax # Assume LegacyMBR is backuped in Sector 6 111 jmp StartReadTo7C00 # EAX = Header/Sector/Tracker/Zero 112 113EfiDbr: 114 cmpb $4, %al # MbrPartitionIndex should < 4 115 jae BadDbr 116 shlw $4, %ax # AX = MBREntrySize * Index 117 addw $0x1be, %ax # AX = MBREntryOffset 118 movw %ax, %di # DI = MBREntryOffset 119 120 # Here we don't use the C/H/S information provided by Partition table 121 # but calculate C/H/S from LBA ourselves 122 # Ci: Cylinder number 123 # Hi: Header number 124 # Si: Sector number 125 movl %es:8(%bp,%di,), %eax # Start LBA 126 movl %eax, %edx 127 shrl $16, %edx # DX:AX = Start LBA 128 # = Ci * (H * S) + Hi * S + (Si - 1) 129 130 # Calculate C/H/S according to LBA 131 movw $0x7bfa, %bp 132 divw 2(%bp) # AX = Hi + H*Ci 133 # DX = Si - 1 134 incw %dx # DX = Si 135 pushw %dx # 0000:7bfa = Si <---- 136 xorw %dx, %dx # DX:AX = Hi + H*Ci 137 divw 4(%bp) # AX = Ci <---- 138 # DX = Hi <---- 139 140StartReadTo7C00: 141 142 movb (%bp), %cl # Si 143 movb %al, %ch # Ci[0-7] 144 orb %ah, %cl # Ci[8,9] 145 movw $0x7c00, %bx # ES:BX = 0000:7C00h 146 movb $0x2, %ah # Function 02h 147 movb $1, %al # 1 Sector 148 movb %dl, %dh # Hi 149 movw $0x600, %bp 150 movb PhysicalDrive(%bp), %dl # Drive number 151 int $0x13 152 jc BadDbr 153 154 155 156# **************************************************************************** 157# Transfer control to BootSector - Jump to 0x0000:0x7C00 158# **************************************************************************** 159 xorw %ax, %ax 160 pushw %ax # PUSH 0x0000 - Segment 161 movw $0x7c00, %di 162 pushw %di # PUSH 0x7C00 - Offset 163 retl # JMP 0x0000:0x7C00 164 165# **************************************************************************** 166# ERROR Condition: 167# **************************************************************************** 168 169BadDbr: 170 pushw %ax 171 movw $0xb800, %ax 172 movw %ax, %es 173 movw $0x60, %ax 174 movw %ax, %ds 175 leaw %cs:ErrorString, %si 176 movw $320, %di 177 popw %ax 178 call A2C 179 movb %ah, 16(%si) 180 movb %al, 18(%si) 181 movw $10, %cx 182 rep 183 movsw 184Halt: 185 jmp Halt 186 187StartString: 188.byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c 189ErrorString: 190.byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, ':', 0x0c, '?', 0x0c, '?', 0x0c 191 192# **************************************************************************** 193# A2C - convert Ascii code stored in AH to character stored in AX 194# **************************************************************************** 195A2C: 196 movb %ah, %al 197 shrb $4, %ah 198 andb $0xF, %al 199 addb '0', %ah 200 addb '0', %al 201 202 cmpb '9', %ah 203 jle A2C_L1 204 addb $7, %ah 205A2C_L1: 206 207 cmpb '9', %al 208 jle A2C_L2 209 addb $7, %al 210A2C_L2: 211 ret 212 213 214# **************************************************************************** 215# PhysicalDrive - Used to indicate which disk to be boot 216# Can be patched by tool 217# **************************************************************************** 218.org 0x01B6 219PhysicalDrive: .byte 0x80 220 221# **************************************************************************** 222# MbrPartitionIndicator - Used to indicate which MBR partition to be boot 223# Can be patched by tool 224# OxFF means boot to legacy MBR. (LBA OFFSET 6) 225# **************************************************************************** 226.org 0x01B7 227MbrPartitionIndicator: .byte 0 228 229# **************************************************************************** 230# Unique MBR signature 231# **************************************************************************** 232.org 0x01B8 233 .ascii "DUET" 234 235# **************************************************************************** 236# Unknown 237# **************************************************************************** 238.org 0x01BC 239 .word 0 240 241# **************************************************************************** 242# MBR Entry - To be patched 243# **************************************************************************** 244.org 0x01BE 245 .long 0,0,0,0 246.org 0x01CE 247 .long 0,0,0,0 248.org 0x01DE 249 .long 0,0,0,0 250.org 0x01EE 251 .long 0,0,0,0 252 253# **************************************************************************** 254# Sector Signature 255# **************************************************************************** 256 257.org 0x01FE 258SectorSignature: 259 .word 0xaa55 # Boot Sector Signature 260 261 262 263