DuetPkg/BootSector/Mbr.S

   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
  77 RelocatedStart:
  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
 109 LegacyMbr:
 110         movl  $0x0000600, %eax                    # Assume LegacyMBR is backuped in Sector 6
 111         jmp   StartReadTo7C00                     # EAX = Header/Sector/Tracker/Zero
 112
 113 EfiDbr:
 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
 140 StartReadTo7C00:
 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
 169 BadDbr:
 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
 184 Halt:
 185     jmp   Halt
 186
 187 StartString:
 188 .byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c
 189 ErrorString:
 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 # ****************************************************************************
 195 A2C:
 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
 205 A2C_L1:
 206
 207     cmpb '9', %al
 208     jle A2C_L2
 209     addb $7, %al
 210 A2C_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
 219 PhysicalDrive:        .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
 227 MbrPartitionIndicator: .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
 258 SectorSignature:
 259   .word     0xaa55      # Boot Sector Signature
 260
 261
 262