mirror of https://github.com/acidanthera/audk.git
262 lines
10 KiB
NASM
262 lines
10 KiB
NASM
;------------------------------------------------------------------------------
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;*
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;* Copyright (c) 2006 - 2007, Intel Corporation. All rights reserved.<BR>
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;* This program and the accompanying materials
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;* are licensed and made available under the terms and conditions of the BSD License
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;* which accompanies this distribution. The full text of the license may be found at
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;* http://opensource.org/licenses/bsd-license.php
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;*
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;* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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;* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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;*
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;* Mbr.asm
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;*
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;* Abstract:
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;*
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;------------------------------------------------------------------------------
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.model small
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; .dosseg
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.stack
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.486p
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.code
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BLOCK_SIZE EQU 0200h
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BLOCK_MASK EQU 01ffh
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BLOCK_SHIFT EQU 9
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; ****************************************************************************
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; Code loaded by BIOS at 0x0000:0x7C00
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; ****************************************************************************
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org 0h
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Start:
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; ****************************************************************************
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; Start Print
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; ****************************************************************************
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mov ax,0b800h
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mov es,ax
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mov ax, 07c0h
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mov ds, ax
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lea si, cs:[StartString]
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mov cx, 10
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mov di, 160
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rep movsw
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; ****************************************************************************
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; Print over
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; ****************************************************************************
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; ****************************************************************************
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; Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600
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; ****************************************************************************
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xor ax, ax ; AX = 0x0000
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mov bx, 07c00h ; BX = 0x7C00
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mov bp, 0600h ; BP = 0x0600
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mov si, OFFSET RelocatedStart ; SI = Offset(RelocatedStart)
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mov cx, 0200h ; CX = 0x0200
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sub cx, si ; CS = 0x0200 - Offset(RelocatedStart)
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lea di, [bp+si] ; DI = 0x0600 + Offset(RelocatedStart)
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lea si, [bx+si] ; BX = 0x7C00 + Offset(RelocatedStart)
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mov ss, ax ; SS = 0x0000
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mov sp, bx ; SP = 0x7C00
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mov es,ax ; ES = 0x0000
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mov ds,ax ; DS = 0x0000
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push ax ; PUSH 0x0000
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push di ; PUSH 0x0600 + Offset(RelocatedStart)
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cld ; Clear the direction flag
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rep movsb ; Copy 0x0200 bytes from 0x7C00 to 0x0600
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retf ; JMP 0x0000:0x0600 + Offset(RelocatedStart)
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; ****************************************************************************
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; Code relocated to 0x0000:0x0600
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; ****************************************************************************
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RelocatedStart:
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; ****************************************************************************
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; Get Driver Parameters to 0x0000:0x7BFC
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; ****************************************************************************
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xor ax,ax ; AX = 0
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mov ss,ax ; SS = 0
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add ax,1000h
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mov ds,ax
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mov sp,07c00h ; SP = 0x7c00
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mov bp,sp ; BP = 0x7c00
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mov ah,8 ; AH = 8 - Get Drive Parameters Function
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mov byte ptr [bp+PhysicalDrive],dl ; BBS defines that BIOS would pass the booting driver number to the loader through DL
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int 13h ; Get Drive Parameters
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xor ax,ax ; AX = 0
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mov al,dh ; AL = DH
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inc al ; MaxHead = AL + 1
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push ax ; 0000:7bfe = MaxHead
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mov al,cl ; AL = CL
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and al,03fh ; MaxSector = AL & 0x3f
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push ax ; 0000:7bfc = MaxSector
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; ****************************************************************************
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; Read Target DBR from hard disk to 0x0000:0x7C00
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; ****************************************************************************
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xor ax, ax
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mov al, byte ptr [bp+MbrPartitionIndicator] ; AX = MbrPartitionIndex
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cmp al, 0ffh ; 0xFF means do legacy MBR boot
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jnz EfiDbr
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LegacyMbr:
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mov eax, 00000600h ; Assume LegacyMBR is backuped in Sector 6
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jmp StartReadTo7C00 ; EAX = Header/Sector/Tracker/Zero
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EfiDbr:
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cmp al, 4 ; MbrPartitionIndex should < 4
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jae BadDbr
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shl ax, 4 ; AX = MBREntrySize * Index
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add ax, 1beh ; AX = MBREntryOffset
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mov di, ax ; DI = MBREntryOffset
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; Here we don't use the C/H/S information provided by Partition table
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; but calculate C/H/S from LBA ourselves
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; Ci: Cylinder number
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; Hi: Header number
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; Si: Sector number
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mov eax, dword ptr es:[bp + di + 8] ; Start LBA
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mov edx, eax
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shr edx, 16 ; DX:AX = Start LBA
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; = Ci * (H * S) + Hi * S + (Si - 1)
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; Calculate C/H/S according to LBA
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mov bp, 7bfah
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div word ptr [bp+2] ; AX = Hi + H*Ci
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; DX = Si - 1
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inc dx ; DX = Si
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push dx ; 0000:7bfa = Si <----
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xor dx, dx ; DX:AX = Hi + H*Ci
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div word ptr [bp+4] ; AX = Ci <----
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; DX = Hi <----
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StartReadTo7C00:
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mov cl, byte ptr [bp] ; Si
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mov ch, al ; Ci[0-7]
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or cl, ah ; Ci[8,9]
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mov bx, 7c00h ; ES:BX = 0000:7C00h
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mov ah, 2h ; Function 02h
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mov al, 1 ; 1 Sector
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mov dh, dl ; Hi
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mov bp, 0600h
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mov dl, byte ptr [bp + PhysicalDrive] ; Drive number
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int 13h
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jc BadDbr
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; ****************************************************************************
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; Transfer control to BootSector - Jump to 0x0000:0x7C00
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; ****************************************************************************
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xor ax, ax
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push ax ; PUSH 0x0000 - Segment
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mov di, 07c00h
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push di ; PUSH 0x7C00 - Offset
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retf ; JMP 0x0000:0x7C00
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; ****************************************************************************
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; ERROR Condition:
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; ****************************************************************************
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BadDbr:
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push ax
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mov ax, 0b800h
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mov es, ax
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mov ax, 060h
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mov ds, ax
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lea si, cs:[ErrorString]
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mov di, 320
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pop ax
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call A2C
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mov [si+16], ah
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mov [si+18], al
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mov cx, 10
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rep movsw
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Halt:
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jmp Halt
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StartString:
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db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch
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ErrorString:
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db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, ':', 0ch, '?', 0ch, '?', 0ch
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; ****************************************************************************
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; A2C - convert Ascii code stored in AH to character stored in AX
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; ****************************************************************************
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A2C:
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mov al, ah
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shr ah, 4
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and al, 0Fh
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add ah, '0'
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add al, '0'
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cmp ah, '9'
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jle @f
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add ah, 7
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@@:
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cmp al, '9'
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jle @f
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add al, 7
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@@:
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ret
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; ****************************************************************************
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; PhysicalDrive - Used to indicate which disk to be boot
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; Can be patched by tool
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; ****************************************************************************
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org 01B6h
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PhysicalDrive db 80h
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; ****************************************************************************
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; MbrPartitionIndicator - Used to indicate which MBR partition to be boot
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; Can be patched by tool
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; OxFF means boot to legacy MBR. (LBA OFFSET 6)
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; ****************************************************************************
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org 01B7h
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MbrPartitionIndicator db 0
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; ****************************************************************************
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; Unique MBR signature
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; ****************************************************************************
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org 01B8h
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db 'DUET'
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; ****************************************************************************
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; Unknown
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; ****************************************************************************
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org 01BCh
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dw 0
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; ****************************************************************************
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; MBR Entry - To be patched
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; ****************************************************************************
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org 01BEh
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dd 0, 0, 0, 0
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org 01CEh
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dd 0, 0, 0, 0
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org 01DEh
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dd 0, 0, 0, 0
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org 01EEh
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dd 0, 0, 0, 0
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; ****************************************************************************
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; Sector Signature
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; ****************************************************************************
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org 01FEh
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SectorSignature:
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dw 0aa55h ; Boot Sector Signature
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end
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