#------------------------------------------------------------------------------ | |
#* | |
#* Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR> | |
#* 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: | |
#* | |
#------------------------------------------------------------------------------ | |
.code16 | |
.equ BLOCK_SIZE, 0x0200 | |
.equ BLOCK_MASK, 0x01ff | |
.equ BLOCK_SHIFT, 9 | |
# **************************************************************************** | |
# Code loaded by BIOS at 0x0000:0x7C00 | |
# **************************************************************************** | |
.org 0x0 | |
.global _start | |
_start: | |
# **************************************************************************** | |
# Start Print | |
# **************************************************************************** | |
movw $0xb800, %ax | |
movw %ax, %es | |
movw $0x7c0, %ax | |
movw %ax, %ds | |
leaw %cs:StartString, %si | |
movw $10, %cx | |
movw $160, %di | |
rep | |
movsw | |
# **************************************************************************** | |
# Print over | |
# **************************************************************************** | |
# **************************************************************************** | |
# Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600 | |
# **************************************************************************** | |
xorw %ax, %ax # AX = 0x0000 | |
movw $0x7c00, %bx # BX = 0x7C00 | |
movw $0x600, %bp # BP = 0x0600 | |
movw $RelocatedStart, %si # SI = Offset(RelocatedStart) | |
movw $0x200, %cx # CX = 0x0200 | |
subw %si, %cx # CS = 0x0200 - Offset(RelocatedStart) | |
leaw (%bp,%si,), %di # DI = 0x0600 + Offset(RelocatedStart) | |
leaw (%bx,%si,), %si # BX = 0x7C00 + Offset(RelocatedStart) | |
movw %ax, %ss # SS = 0x0000 | |
movw %bx, %sp # SP = 0x7C00 | |
movw %ax, %es # ES = 0x0000 | |
movw %ax, %ds # DS = 0x0000 | |
pushw %ax # PUSH 0x0000 | |
pushw %di # PUSH 0x0600 + Offset(RelocatedStart) | |
cld # Clear the direction flag | |
rep | |
movsb # Copy 0x0200 bytes from 0x7C00 to 0x0600 | |
retl # JMP 0x0000:0x0600 + Offset(RelocatedStart) | |
# **************************************************************************** | |
# Code relocated to 0x0000:0x0600 | |
# **************************************************************************** | |
RelocatedStart: | |
# **************************************************************************** | |
# Get Driver Parameters to 0x0000:0x7BFC | |
# **************************************************************************** | |
xorw %ax, %ax # AX = 0 | |
movw %ax, %ss # SS = 0 | |
addw $0x1000, %ax | |
movw %ax, %ds | |
movw $0x7c00, %sp # SP = 0x7c00 | |
movw %sp, %bp # BP = 0x7c00 | |
movb $8, %ah # AH = 8 - Get Drive Parameters Function | |
movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL | |
int $0x13 # Get Drive Parameters | |
xorw %ax, %ax # AX = 0 | |
movb %dh, %al # AL = DH | |
incb %al # MaxHead = AL + 1 | |
pushw %ax # 0000:7bfe = MaxHead | |
movb %cl, %al # AL = CL | |
andb $0x3f, %al # MaxSector = AL & 0x3f | |
pushw %ax # 0000:7bfc = MaxSector | |
# **************************************************************************** | |
# Read Target DBR from hard disk to 0x0000:0x7C00 | |
# **************************************************************************** | |
xorw %ax, %ax | |
movb MbrPartitionIndicator(%bp), %al # AX = MbrPartitionIndex | |
cmpb $0xff, %al # 0xFF means do legacy MBR boot | |
jnz EfiDbr | |
LegacyMbr: | |
movl $0x0000600, %eax # Assume LegacyMBR is backuped in Sector 6 | |
jmp StartReadTo7C00 # EAX = Header/Sector/Tracker/Zero | |
EfiDbr: | |
cmpb $4, %al # MbrPartitionIndex should < 4 | |
jae BadDbr | |
shlw $4, %ax # AX = MBREntrySize * Index | |
addw $0x1be, %ax # AX = MBREntryOffset | |
movw %ax, %di # 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 | |
movl %es:8(%bp,%di,), %eax # Start LBA | |
movl %eax, %edx | |
shrl $16, %edx # DX:AX = Start LBA | |
# = Ci * (H * S) + Hi * S + (Si - 1) | |
# Calculate C/H/S according to LBA | |
movw $0x7bfa, %bp | |
divw 2(%bp) # AX = Hi + H*Ci | |
# DX = Si - 1 | |
incw %dx # DX = Si | |
pushw %dx # 0000:7bfa = Si <---- | |
xorw %dx, %dx # DX:AX = Hi + H*Ci | |
divw 4(%bp) # AX = Ci <---- | |
# DX = Hi <---- | |
StartReadTo7C00: | |
movb (%bp), %cl # Si | |
movb %al, %ch # Ci[0-7] | |
orb %ah, %cl # Ci[8,9] | |
movw $0x7c00, %bx # ES:BX = 0000:7C00h | |
movb $0x2, %ah # Function 02h | |
movb $1, %al # 1 Sector | |
movb %dl, %dh # Hi | |
movw $0x600, %bp | |
movb PhysicalDrive(%bp), %dl # Drive number | |
int $0x13 | |
jc BadDbr | |
# **************************************************************************** | |
# Transfer control to BootSector - Jump to 0x0000:0x7C00 | |
# **************************************************************************** | |
xorw %ax, %ax | |
pushw %ax # PUSH 0x0000 - Segment | |
movw $0x7c00, %di | |
pushw %di # PUSH 0x7C00 - Offset | |
retl # JMP 0x0000:0x7C00 | |
# **************************************************************************** | |
# ERROR Condition: | |
# **************************************************************************** | |
BadDbr: | |
pushw %ax | |
movw $0xb800, %ax | |
movw %ax, %es | |
movw $0x60, %ax | |
movw %ax, %ds | |
leaw %cs:ErrorString, %si | |
movw $320, %di | |
popw %ax | |
call A2C | |
movb %ah, 16(%si) | |
movb %al, 18(%si) | |
movw $10, %cx | |
rep | |
movsw | |
Halt: | |
jmp Halt | |
StartString: | |
.byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c | |
ErrorString: | |
.byte 'M', 0x0c, 'B', 0x0c, 'R', 0x0c, ' ', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, ':', 0x0c, '?', 0x0c, '?', 0x0c | |
# **************************************************************************** | |
# A2C - convert Ascii code stored in AH to character stored in AX | |
# **************************************************************************** | |
A2C: | |
movb %ah, %al | |
shrb $4, %ah | |
andb $0xF, %al | |
addb '0', %ah | |
addb '0', %al | |
cmpb '9', %ah | |
jle A2C_L1 | |
addb $7, %ah | |
A2C_L1: | |
cmpb '9', %al | |
jle A2C_L2 | |
addb $7, %al | |
A2C_L2: | |
ret | |
# **************************************************************************** | |
# PhysicalDrive - Used to indicate which disk to be boot | |
# Can be patched by tool | |
# **************************************************************************** | |
.org 0x01B6 | |
PhysicalDrive: .byte 0x80 | |
# **************************************************************************** | |
# 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 0x01B7 | |
MbrPartitionIndicator: .byte 0 | |
# **************************************************************************** | |
# Unique MBR signature | |
# **************************************************************************** | |
.org 0x01B8 | |
.ascii "DUET" | |
# **************************************************************************** | |
# Unknown | |
# **************************************************************************** | |
.org 0x01BC | |
.word 0 | |
# **************************************************************************** | |
# MBR Entry - To be patched | |
# **************************************************************************** | |
.org 0x01BE | |
.long 0,0,0,0 | |
.org 0x01CE | |
.long 0,0,0,0 | |
.org 0x01DE | |
.long 0,0,0,0 | |
.org 0x01EE | |
.long 0,0,0,0 | |
# **************************************************************************** | |
# Sector Signature | |
# **************************************************************************** | |
.org 0x01FE | |
SectorSignature: | |
.word 0xaa55 # Boot Sector Signature | |