| ;------------------------------------------------------------------------------ | |
| ;* | |
| ;* 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 | |