;------------------------------------------------------------------------------ ;* ;* 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