#------------------------------------------------------------------------------ #* #* 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