DuetPkg/BootSector/bs16.S

   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 #*    bs16.asm
  13 #*
  14 #*   Abstract:
  15 #*
  16 #------------------------------------------------------------------------------
  17
  18         #.MODEL small
  19         .stack:
  20         .486p:
  21         .code16
  22
  23 .equ                      FAT_DIRECTORY_ENTRY_SIZE, 0x020
  24 .equ                      FAT_DIRECTORY_ENTRY_SHIFT, 5
  25 .equ                      BLOCK_SIZE, 0x0200
  26 .equ                      BLOCK_MASK, 0x01ff
  27 .equ                      BLOCK_SHIFT, 9
  28                                                # "EFILDR_____"
  29 .equ                      LOADER_FILENAME_PART1, 0x04c494645    # "EFIL"
  30 .equ                      LOADER_FILENAME_PART2, 0x036315244    # "DR16"
  31 .equ                      LOADER_FILENAME_PART3, 0x020202036    # "6___"
  32
  33         .org 0x0
  34 ASM_GLOBAL _start
  35 _start:
  36 Ia32Jump:
  37   jmp   BootSectorEntryPoint  # JMP inst                  - 3 bytes
  38   nop
  39
  40 OemId:              .ascii   "INTEL   "       # OemId               - 8 bytes
  41 # BPB data below will be fixed by tool
  42 SectorSize:         .word  0                  # Sector Size         - 16 bits
  43 SectorsPerCluster:  .byte  0                  # Sector Per Cluster  - 8 bits
  44 ReservedSectors:    .word  0                  # Reserved Sectors    - 16 bits
  45 NoFats:             .byte  0                  # Number of FATs      - 8 bits
  46 RootEntries:        .word  0                  # Root Entries        - 16 bits
  47 Sectors:            .word  0                  # Number of Sectors   - 16 bits
  48 Media:              .byte  0                  # Media               - 8 bits  - ignored
  49 SectorsPerFat:      .word  0                  # Sectors Per FAT     - 16 bits
  50 SectorsPerTrack:    .word  0                  # Sectors Per Track   - 16 bits - ignored
  51 Heads:              .word  0                  # Heads               - 16 bits - ignored
  52 HiddenSectors:      .long  0                  # Hidden Sectors      - 32 bits - ignored
  53 LargeSectors:       .long  0                  # Large Sectors       - 32 bits
  54 PhysicalDrive:      .byte  0                  # PhysicalDriveNumber - 8 bits  - ignored
  55 CurrentHead:        .byte  0                  # Current Head        - 8 bits
  56 Signature:          .byte  0                  # Signature           - 8 bits  - ignored
  57 VolId:              .ascii "    "             # Volume Serial Number- 4 bytes
  58 FatLabel:           .ascii "           "      # Label               - 11 bytes
  59 SystemId:           .ascii "FAT12   "         # SystemId            - 8 bytes
  60
  61 BootSectorEntryPoint:
  62         #ASSUME ds:@code
  63         #ASSUME ss:@code
  64
  65 # ****************************************************************************
  66 # Start Print
  67 # ****************************************************************************
  68   movw $StartString, %si
  69   call PrintString
  70
  71 # ****************************************************************************
  72 # Print over
  73 # ****************************************************************************
  74
  75   movw  %cs, %ax      # ax = 0
  76   movw  %ax, %ss      # ss = 0
  77   addw  $0x1000, %ax
  78   movw  %ax, %ds
  79
  80   movw  $0x7c00, %sp  # sp = 0x7c00
  81   movw  %sp, %bp      # bp = 0x7c00
  82
  83   movb  $8, %ah                             # ah = 8 - Get Drive Parameters Function
  84   movb  %dl, PhysicalDrive(%bp)             # BBS defines that BIOS would pass the booting driver number to the loader through DL
  85   int   $0x13                               # Get Drive Parameters
  86   xorw  %ax, %ax                # ax = 0
  87   movb  %dh, %al                # al = dh
  88   incb  %al                     # MaxHead = al + 1
  89   pushw %ax                     # 0000:7bfe = MaxHead
  90   movb  %cl, %al                # al = cl
  91   andb  $0x3f, %al              # MaxSector = al & 0x3f
  92   pushw %ax                     # 0000:7bfc = MaxSector
  93
  94   cmpw  $0xaa55, SectorSignature(%bp)         # Verify Boot Sector Signature
  95   jne   BadBootSector
  96   movw  RootEntries(%bp), %cx             # cx = RootEntries
  97   shlw  $FAT_DIRECTORY_ENTRY_SHIFT, %cx   # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes
  98   movw  %cx, %bx                          # bx = size of the Root Directory in bytes
  99   andw  $BLOCK_MASK, %bx                  # See if it is an even number of sectors long
 100   jne   BadBootSector                     # If is isn't, then the boot sector is bad.
 101   movw  %cx, %bx                          # bx = size of the Root Directory in bytes
 102   shrw  $BLOCK_SHIFT, %bx                 # bx = size of Root Directory in sectors
 103   movb  NoFats(%bp), %al                  # al = NoFats
 104   xorb  %ah, %ah                          # ah = 0  ==> ax = NoFats
 105   mulw  SectorsPerFat(%bp)                # ax = NoFats * SectorsPerFat
 106   addw  ReservedSectors(%bp), %ax         # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA
 107   pushw %ds
 108   popw  %es
 109   xorw  %di, %di                          # Store directory in es:di = 1000:0000
 110   call  ReadBlocks                        # Read entire Root Directory
 111   addw  %bx, %ax                          # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)
 112   movw  %ax, (%bp)                        # Save FirstClusterLBA (FirstDataSector) for later use
 113
 114   # dx - variable storage (initial value is 0)
 115   # bx - loader (initial value is 0)
 116   xorw  %dx, %dx
 117   xorw  %bx, %bx
 118
 119 FindEFILDR:
 120   cmpl   $LOADER_FILENAME_PART1, (%di)        # Compare to "EFIL"
 121   jne   FindVARSTORE
 122         cmpl   $LOADER_FILENAME_PART2, 4(%di)
 123   jne   FindVARSTORE
 124   cmpl   $LOADER_FILENAME_PART3, 7(%di)
 125   jne   FindVARSTORE
 126   movw  26(%di), %bx                      # bx = Start Cluster for EFILDR  <----------------------------------
 127   testw %dx, %dx
 128   je    FindNext                          # Efivar.bin is not loaded
 129   jmp   FoundAll
 130
 131 FindVARSTORE:
 132   ##if the file is not loader file, see if it's "EFIVAR  BIN"
 133   cmpl  $0x56494645, (%di)                # Compare to "EFIV"
 134   jne   FindNext
 135   cmpl  $0x20205241, 4(%di)               # Compare to "AR  "
 136   jne   FindNext
 137   cmpl  $0x4e494220, 7(%di)               # Compare to " BIN"
 138   jne   FindNext
 139   movw  %di, %dx                          # dx = Offset of Start Cluster for Efivar.bin <---------------------
 140   addw  $26, %dx
 141   testw %bx, %bx
 142   je    FindNext                          # Efildr is not loaded
 143   jmp   FoundAll
 144
 145 FindNext:
 146   # go to next find
 147   addw  $FAT_DIRECTORY_ENTRY_SIZE, %di    # Increment di
 148   subw  $FAT_DIRECTORY_ENTRY_SIZE, %cx    # Decrement cx
 149   # TODO: jump to FindVarStore if ...
 150   jne   FindEFILDR
 151   jmp   NotFoundAll
 152
 153 FoundAll:
 154 FoundEFILDR:
 155   movw    %bx, %cx                            # cx = Start Cluster for EFILDR  <----------------------------------
 156   movw    %cs, %ax                            # Destination = 2000:0000
 157   addw    $0x2000, %ax
 158   movw    %ax, %es
 159   xorw    %di, %di
 160 ReadFirstClusterOfEFILDR:
 161   movw    %cx, %ax                            # ax = StartCluster
 162   subw    $2, %ax                             # ax = StartCluster - 2
 163   xorb    %bh, %bh
 164   movb    SectorsPerCluster(%bp), %bl         # bx = SectorsPerCluster
 165   pushw   %dx
 166   mulw    %bx
 167   popw    %dx                                 # ax = (StartCluster - 2) * SectorsPerCluster
 168   addw    (%bp), %ax                          # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
 169   xorb    %bh, %bh
 170   movb    SectorsPerCluster(%bp), %bl         # bx = Number of Sectors in a cluster
 171   pushw   %es
 172   call    ReadBlocks
 173   popw    %ax
 174 JumpIntoFirstSectorOfEFILDR:
 175   movw    %ax, JumpSegment(%bp)
 176 JumpFarInstruction:
 177   .byte   0xea
 178 JumpOffset:
 179   .word   0x000
 180 JumpSegment:
 181   .word   0x2000
 182
 183
 184 PrintString:
 185   movw $0xb800, %ax
 186   movw %ax, %es
 187   movw $0x7c0, %ax
 188   movw %ax, %ds
 189   movw $7, %cx
 190   movw $160, %di
 191   rep
 192   movsw
 193   ret
 194 # ****************************************************************************
 195 # ReadBlocks - Reads a set of blocks from a block device
 196 #
 197 # AX    = Start LBA
 198 # BX    = Number of Blocks to Read
 199 # ES:DI = Buffer to store sectors read from disk
 200 # ****************************************************************************
 201
 202 # cx = Blocks
 203 # bx = NumberOfBlocks
 204 # si = StartLBA
 205
 206 ReadBlocks:
 207   pusha
 208   addl    LBAOffsetForBootSector(%bp), %eax            # Add LBAOffsetForBootSector to Start LBA
 209   addl    HiddenSectors(%bp), %eax            # Add HiddenSectors to Start LBA
 210   movl    %eax, %esi                          # esi = Start LBA
 211   movw    %bx, %cx                            # cx = Number of blocks to read
 212 ReadCylinderLoop:
 213   movw    $0x7bfc, %bp                        # bp = 0x7bfc
 214   movl    %esi, %eax                          # eax = Start LBA
 215   xorl    %edx, %edx                          # edx = 0
 216   movzwl  (%bp), %ebx                         # bx = MaxSector
 217   divl    %ebx                                # ax = StartLBA / MaxSector
 218   incw    %dx                                 # dx = (StartLBA % MaxSector) + 1
 219   subw    %dx, %bx                            # bx = MaxSector - Sector
 220   incw    %bx                                 # bx = MaxSector - Sector + 1
 221   cmpw    %bx, %cx                            # Compare (Blocks) to (MaxSector - Sector + 1)
 222   jg      LimitTransfer
 223   movw    %cx, %bx                            # bx = Blocks
 224 LimitTransfer:
 225   pushw   %cx
 226   movb    %dl, %cl                            # cl = (StartLBA % MaxSector) + 1 = Sector
 227   xorw    %dx, %dx                            # dx = 0
 228   divw    2(%bp)                              # ax = ax / (MaxHead + 1) = Cylinder
 229                                               # dx = ax % (MaxHead + 1) = Head
 230
 231   pushw   %bx                                 # Save number of blocks to transfer
 232   movb    %dl, %dh                            # dh = Head
 233   movw    $0x7c00, %bp                        # bp = 0x7c00
 234   movb    PhysicalDrive(%bp), %dl             # dl = Drive Number
 235   movb    %al, %ch                            # ch = Cylinder
 236   movb    %bl, %al                            # al = Blocks
 237   movb    $2, %ah                             # ah = Function 2
 238   movw    %di, %bx                            # es:bx = Buffer address
 239   int     $0x13
 240   jc      DiskError
 241   popw    %bx
 242   popw    %cx
 243   movzwl  %bx, %ebx
 244   addl    %ebx, %esi                          # StartLBA = StartLBA + NumberOfBlocks
 245   subw    %bx, %cx                            # Blocks = Blocks - NumberOfBlocks
 246   movw    %es, %ax
 247   shlw    $(BLOCK_SHIFT-4),%bx
 248   addw    %bx, %ax
 249   movw    %ax, %es                            # es:di = es:di + NumberOfBlocks*BLOCK_SIZE
 250   cmpw    $0, %cx
 251   jne     ReadCylinderLoop
 252   popa
 253   ret
 254
 255 # ****************************************************************************
 256 # ERROR Condition:
 257 # ****************************************************************************
 258 NotFoundAll:
 259   ## if we found EFILDR, continue
 260   testw %bx, %bx
 261   jne  FoundEFILDR
 262 BadBootSector:
 263 DiskError:
 264   movw $ErrorString, %si
 265   call PrintString
 266 Halt:
 267   jmp   Halt
 268
 269 StartString:
 270   .byte  'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c
 271 ErrorString:
 272   .byte  'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c
 273
 274 # ****************************************************************************
 275 # LBA Offset for BootSector, need patched by tool for HD boot.
 276 # ****************************************************************************
 277
 278   .org 0x01fa
 279 LBAOffsetForBootSector:
 280   .long     0x0
 281
 282 # ****************************************************************************
 283 # Sector Signature
 284 # ****************************************************************************
 285
 286   .org 0x01fe
 287 SectorSignature:
 288   .word     0xaa55      # Boot Sector Signature
 289
 290
 291