DuetPkg/BootSector/Mbr.asm

   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     .model  small
  19 ;   .dosseg
  20     .stack
  21     .486p
  22     .code
  23
  24 BLOCK_SIZE                EQU     0200h
  25 BLOCK_MASK                EQU     01ffh
  26 BLOCK_SHIFT               EQU     9
  27
  28 ; ****************************************************************************
  29 ; Code loaded by BIOS at 0x0000:0x7C00
  30 ; ****************************************************************************
  31
  32         org 0h
  33 Start:
  34
  35 ; ****************************************************************************
  36 ; Start Print
  37 ; ****************************************************************************
  38
  39         mov  ax,0b800h
  40         mov  es,ax
  41         mov  ax, 07c0h
  42         mov  ds, ax
  43         lea  si, cs:[StartString]
  44         mov  cx, 10
  45         mov  di, 160
  46         rep  movsw
  47
  48 ; ****************************************************************************
  49 ; Print over
  50 ; ****************************************************************************
  51
  52 ; ****************************************************************************
  53 ; Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600
  54 ; ****************************************************************************
  55         xor   ax, ax                              ; AX = 0x0000
  56         mov   bx, 07c00h                          ; BX = 0x7C00
  57         mov   bp, 0600h                           ; BP = 0x0600
  58         mov   si, OFFSET RelocatedStart           ; SI = Offset(RelocatedStart)
  59         mov   cx, 0200h                           ; CX = 0x0200
  60         sub   cx, si                              ; CS = 0x0200 - Offset(RelocatedStart)
  61         lea   di, [bp+si]                         ; DI = 0x0600 + Offset(RelocatedStart)
  62         lea   si, [bx+si]                         ; BX = 0x7C00 + Offset(RelocatedStart)
  63         mov   ss, ax                              ; SS = 0x0000
  64         mov   sp, bx                              ; SP = 0x7C00
  65         mov   es,ax                               ; ES = 0x0000
  66         mov   ds,ax                               ; DS = 0x0000
  67         push  ax                                  ; PUSH 0x0000
  68         push  di                                  ; PUSH 0x0600 + Offset(RelocatedStart)
  69         cld                                       ; Clear the direction flag
  70         rep   movsb                               ; Copy 0x0200 bytes from 0x7C00 to 0x0600
  71         retf                                      ; 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         xor   ax,ax                               ; AX = 0
  83         mov   ss,ax                               ; SS = 0
  84         add   ax,1000h
  85         mov   ds,ax
  86
  87         mov   sp,07c00h                           ; SP = 0x7c00
  88         mov   bp,sp                               ; BP = 0x7c00
  89
  90         mov   ah,8                                ; AH = 8 - Get Drive Parameters Function
  91         mov   byte ptr [bp+PhysicalDrive],dl      ; BBS defines that BIOS would pass the booting driver number to the loader through DL
  92         int   13h                                 ; Get Drive Parameters
  93         xor   ax,ax                               ; AX = 0
  94         mov   al,dh                               ; AL = DH
  95         inc   al                                  ; MaxHead = AL + 1
  96         push  ax                                  ; 0000:7bfe = MaxHead
  97         mov   al,cl                               ; AL = CL
  98         and   al,03fh                             ; MaxSector = AL & 0x3f
  99         push  ax                                  ; 0000:7bfc = MaxSector
 100
 101 ; ****************************************************************************
 102 ; Read Target DBR from hard disk to 0x0000:0x7C00
 103 ; ****************************************************************************
 104
 105         xor   ax, ax
 106         mov   al, byte ptr [bp+MbrPartitionIndicator]  ; AX = MbrPartitionIndex
 107         cmp   al, 0ffh                                 ; 0xFF means do legacy MBR boot
 108         jnz   EfiDbr
 109 LegacyMbr:
 110         mov   eax, 00000600h                      ; Assume LegacyMBR is backuped in Sector 6
 111         jmp   StartReadTo7C00                     ; EAX = Header/Sector/Tracker/Zero
 112
 113 EfiDbr:
 114         cmp   al, 4                               ; MbrPartitionIndex should < 4
 115         jae   BadDbr
 116         shl   ax, 4                               ; AX  = MBREntrySize * Index
 117         add   ax, 1beh                            ; AX  = MBREntryOffset
 118         mov   di, ax                              ; 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         mov   eax, dword ptr es:[bp + di + 8]     ; Start LBA
 126         mov   edx, eax
 127         shr   edx, 16                             ; DX:AX = Start LBA
 128                                                   ;       = Ci * (H * S) + Hi * S + (Si - 1)
 129
 130         ; Calculate C/H/S according to LBA
 131         mov   bp, 7bfah
 132         div   word ptr [bp+2]                     ; AX = Hi + H*Ci
 133                                                   ; DX = Si - 1
 134         inc   dx                                  ; DX = Si
 135         push  dx                                  ; 0000:7bfa = Si  <----
 136         xor   dx, dx                              ; DX:AX = Hi + H*Ci
 137         div   word ptr [bp+4]                     ; AX = Ci         <----
 138                                                   ; DX = Hi         <----
 139
 140 StartReadTo7C00:
 141
 142         mov   cl, byte ptr [bp]                   ; Si
 143         mov   ch, al                              ; Ci[0-7]
 144         or    cl, ah                              ; Ci[8,9]
 145         mov   bx, 7c00h                           ; ES:BX = 0000:7C00h
 146         mov   ah, 2h                              ; Function 02h
 147         mov   al, 1                               ; 1 Sector
 148         mov   dh, dl                              ; Hi
 149         mov   bp, 0600h
 150         mov   dl, byte ptr [bp + PhysicalDrive]   ; Drive number
 151         int   13h
 152         jc    BadDbr
 153
 154
 155
 156 ; ****************************************************************************
 157 ; Transfer control to BootSector - Jump to 0x0000:0x7C00
 158 ; ****************************************************************************
 159         xor   ax, ax
 160         push  ax                                  ; PUSH 0x0000 - Segment
 161         mov   di, 07c00h
 162         push  di                                  ; PUSH 0x7C00 - Offset
 163         retf                                      ; JMP 0x0000:0x7C00
 164
 165 ; ****************************************************************************
 166 ; ERROR Condition:
 167 ; ****************************************************************************
 168
 169 BadDbr:
 170     push ax
 171     mov  ax, 0b800h
 172     mov  es, ax
 173     mov  ax, 060h
 174     mov  ds, ax
 175     lea  si, cs:[ErrorString]
 176     mov  di, 320
 177     pop  ax
 178     call A2C
 179     mov  [si+16], ah
 180     mov  [si+18], al
 181     mov  cx, 10
 182     rep  movsw
 183 Halt:
 184     jmp   Halt
 185
 186 StartString:
 187     db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch
 188 ErrorString:
 189     db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, ':', 0ch, '?', 0ch, '?', 0ch
 190
 191 ; ****************************************************************************
 192 ; A2C - convert Ascii code stored in AH to character stored in AX
 193 ; ****************************************************************************
 194 A2C:
 195     mov  al, ah
 196     shr  ah, 4
 197     and  al, 0Fh
 198     add  ah, '0'
 199     add  al, '0'
 200
 201     cmp  ah, '9'
 202     jle  @f
 203     add  ah, 7
 204 @@:
 205
 206     cmp al, '9'
 207     jle @f
 208     add al, 7
 209 @@:
 210     ret
 211
 212
 213 ; ****************************************************************************
 214 ; PhysicalDrive - Used to indicate which disk to be boot
 215 ;                 Can be patched by tool
 216 ; ****************************************************************************
 217     org   01B6h
 218 PhysicalDrive         db  80h
 219
 220 ; ****************************************************************************
 221 ; MbrPartitionIndicator - Used to indicate which MBR partition to be boot
 222 ;                         Can be patched by tool
 223 ;                         OxFF means boot to legacy MBR. (LBA OFFSET 6)
 224 ; ****************************************************************************
 225     org   01B7h
 226 MbrPartitionIndicator db 0
 227
 228 ; ****************************************************************************
 229 ; Unique MBR signature
 230 ; ****************************************************************************
 231     org   01B8h
 232     db 'DUET'
 233
 234 ; ****************************************************************************
 235 ; Unknown
 236 ; ****************************************************************************
 237     org   01BCh
 238     dw 0
 239
 240 ; ****************************************************************************
 241 ; MBR Entry - To be patched
 242 ; ****************************************************************************
 243     org   01BEh
 244     dd 0, 0, 0, 0
 245     org   01CEh
 246     dd 0, 0, 0, 0
 247     org   01DEh
 248     dd 0, 0, 0, 0
 249     org   01EEh
 250     dd 0, 0, 0, 0
 251
 252 ; ****************************************************************************
 253 ; Sector Signature
 254 ; ****************************************************************************
 255
 256   org 01FEh
 257 SectorSignature:
 258   dw        0aa55h      ; Boot Sector Signature
 259
 260   end
 261