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