| #------------------------------------------------------------------------------ |
| #* |
| #* 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: |
| #* |
| #------------------------------------------------------------------------------ |
| |
| .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 |
| |
| |
| |
