#------------------------------------------------------------------------------ #* #* 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. #* #* bootsect.asm #* #* Abstract: #* #------------------------------------------------------------------------------ #.MODEL small .stack: .486p: .code16 .equ FAT_DIRECTORY_ENTRY_SIZE, 0x020 .equ FAT_DIRECTORY_ENTRY_SHIFT, 5 .equ BLOCK_SIZE, 0x0200 .equ BLOCK_MASK, 0x01ff .equ BLOCK_SHIFT, 9 # "EFILDR_____" .equ LOADER_FILENAME_PART1, 0x04c494645 # "EFIL" .equ LOADER_FILENAME_PART2, 0x020205244 # "DR__" .equ LOADER_FILENAME_PART3, 0x020202020 # "____" .org 0x0 .global _start _start: Ia32Jump: jmp BootSectorEntryPoint # JMP inst - 3 bytes nop OemId: .ascii "INTEL " # OemId - 8 bytes # BPB data below will be fixed by tool SectorSize: .word 0 # Sector Size - 16 bits SectorsPerCluster: .byte 0 # Sector Per Cluster - 8 bits ReservedSectors: .word 0 # Reserved Sectors - 16 bits NoFats: .byte 0 # Number of FATs - 8 bits RootEntries: .word 0 # Root Entries - 16 bits Sectors: .word 0 # Number of Sectors - 16 bits Media: .byte 0 # Media - 8 bits - ignored SectorsPerFat: .word 0 # Sectors Per FAT - 16 bits SectorsPerTrack: .word 0 # Sectors Per Track - 16 bits - ignored Heads: .word 0 # Heads - 16 bits - ignored HiddenSectors: .long 0 # Hidden Sectors - 32 bits - ignored LargeSectors: .long 0 # Large Sectors - 32 bits PhysicalDrive: .byte 0 # PhysicalDriveNumber - 8 bits - ignored CurrentHead: .byte 0 # Current Head - 8 bits Signature: .byte 0 # Signature - 8 bits - ignored VolId: .ascii " " # Volume Serial Number- 4 bytes FatLabel: .ascii " " # Label - 11 bytes SystemId: .ascii "FAT12 " # SystemId - 8 bytes BootSectorEntryPoint: #ASSUME ds:@code #ASSUME ss:@code # **************************************************************************** # Start Print # **************************************************************************** movw $StartString, %si call PrintString # **************************************************************************** # Print over # **************************************************************************** movw %cs, %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 cmpw $0xaa55, SectorSignature(%bp) # Verify Boot Sector Signature jne BadBootSector movw RootEntries(%bp), %cx # cx = RootEntries shlw $FAT_DIRECTORY_ENTRY_SHIFT, %cx # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes movw %cx, %bx # bx = size of the Root Directory in bytes andw $BLOCK_MASK, %bx # See if it is an even number of sectors long jne BadBootSector # If is isn't, then the boot sector is bad. movw %cx, %bx # bx = size of the Root Directory in bytes shrw $BLOCK_SHIFT, %bx # bx = size of Root Directory in sectors movb NoFats(%bp), %al # al = NoFats xorb %ah, %ah # ah = 0 ==> ax = NoFats mulw SectorsPerFat(%bp) # ax = NoFats * SectorsPerFat addw ReservedSectors(%bp), %ax # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA pushw %ds popw %es xorw %di, %di # Store directory in es:di = 1000:0000 call ReadBlocks # Read entire Root Directory addw %bx, %ax # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector) movw %ax, (%bp) # Save FirstClusterLBA (FirstDataSector) for later use # dx - variable storage (initial value is 0) # bx - loader (initial value is 0) xorw %dx, %dx xorw %bx, %bx FindEFILDR: cmpl $LOADER_FILENAME_PART1, (%di) # Compare to "EFIL" jne FindVARSTORE cmpl $LOADER_FILENAME_PART2, 4(%di) jne FindVARSTORE cmpl $LOADER_FILENAME_PART3, 7(%di) jne FindVARSTORE movw 26(%di), %bx # bx = Start Cluster for EFILDR <---------------------------------- testw %dx, %dx je FindNext # Efivar.bin is not loaded jmp FoundAll FindVARSTORE: ## if the file is not loader file, see if it's "EFIVAR BIN" cmpl $0x56494645, (%di) # Compare to "EFIV" jne FindNext cmpl $0x20205241, 4(%di) # Compare to "AR " jne FindNext cmpl $0x4e494220, 7(%di) # Compare to " BIN" jne FindNext movw %di, %dx # dx = Offset of Start Cluster for Efivar.bin <--------------------- addw $26, %dx testw %bx, %bx je FindNext # Efildr is not loaded jmp FoundAll FindNext: # go to next find addw $FAT_DIRECTORY_ENTRY_SIZE, %di # Increment di subw $FAT_DIRECTORY_ENTRY_SIZE, %cx # Decrement cx # TODO: jump to FindVarStore if ... jne FindEFILDR jmp NotFoundAll FoundAll: FoundEFILDR: movw %bx, %cx # cx = Start Cluster for EFILDR <---------------------------------- movw %cs, %ax # Destination = 2000:0000 addw $0x2000, %ax movw %ax, %es xorw %di, %di ReadFirstClusterOfEFILDR: movw %cx, %ax # ax = StartCluster subw $2, %ax # ax = StartCluster - 2 xorb %bh, %bh movb SectorsPerCluster(%bp), %bl # bx = SectorsPerCluster pushw %dx mulw %bx popw %dx # ax = (StartCluster - 2) * SectorsPerCluster addw (%bp), %ax # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster xorb %bh, %bh movb SectorsPerCluster(%bp), %bl # bx = Number of Sectors in a cluster pushw %es call ReadBlocks popw %ax JumpIntoFirstSectorOfEFILDR: movw %ax, JumpSegment(%bp) JumpFarInstruction: .byte 0xea JumpOffset: .word 0x000 JumpSegment: .word 0x2000 PrintString: movw $0xb800, %ax movw %ax, %es movw $0x7c0, %ax movw %ax, %ds movw $7, %cx movw $160, %di rep movsw ret # **************************************************************************** # ReadBlocks - Reads a set of blocks from a block device # # AX = Start LBA # BX = Number of Blocks to Read # ES:DI = Buffer to store sectors read from disk # **************************************************************************** # cx = Blocks # bx = NumberOfBlocks # si = StartLBA ReadBlocks: pusha addl LBAOffsetForBootSector(%bp), %eax # Add LBAOffsetForBootSector to Start LBA addl HiddenSectors(%bp), %eax # Add HiddenSectors to Start LBA movl %eax, %esi # esi = Start LBA movw %bx, %cx # cx = Number of blocks to read ReadCylinderLoop: movw $0x7bfc, %bp # bp = 0x7bfc movl %esi, %eax # eax = Start LBA xorl %edx, %edx # edx = 0 movzwl (%bp), %ebx # bx = MaxSector divl %ebx # ax = StartLBA / MaxSector incw %dx # dx = (StartLBA % MaxSector) + 1 subw %dx, %bx # bx = MaxSector - Sector incw %bx # bx = MaxSector - Sector + 1 cmpw %bx, %cx # Compare (Blocks) to (MaxSector - Sector + 1) jg LimitTransfer movw %cx, %bx # bx = Blocks LimitTransfer: pushw %cx movb %dl, %cl # cl = (StartLBA % MaxSector) + 1 = Sector xorw %dx, %dx # dx = 0 divw 2(%bp) # ax = ax / (MaxHead + 1) = Cylinder # dx = ax % (MaxHead + 1) = Head pushw %bx # Save number of blocks to transfer movb %dl, %dh # dh = Head movw $0x7c00, %bp # bp = 0x7c00 movb PhysicalDrive(%bp), %dl # dl = Drive Number movb %al, %ch # ch = Cylinder movb %bl, %al # al = Blocks movb $2, %ah # ah = Function 2 movw %di, %bx # es:bx = Buffer address int $0x13 jc DiskError popw %bx popw %cx movzwl %bx, %ebx addl %ebx, %esi # StartLBA = StartLBA + NumberOfBlocks subw %bx, %cx # Blocks = Blocks - NumberOfBlocks movw %es, %ax shlw $(BLOCK_SHIFT-4), %bx addw %bx, %ax movw %ax, %es # es:di = es:di + NumberOfBlocks*BLOCK_SIZE cmpw $0, %cx jne ReadCylinderLoop popa ret # **************************************************************************** # ERROR Condition: # **************************************************************************** NotFoundAll: ## if we found EFILDR, continue testw %bx, %bx jne FoundEFILDR BadBootSector: DiskError: movw $ErrorString, %si call PrintString Halt: jmp Halt StartString: .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c ErrorString: .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c # **************************************************************************** # LBA Offset for BootSector, need patched by tool for HD boot. # **************************************************************************** .org 0x01fa # Comment it for pass build. Should optimise code size. LBAOffsetForBootSector: .long 0x0 # **************************************************************************** # Sector Signature # **************************************************************************** .org 0x01fe # Comment it for pass build. SectorSignature: .word 0xaa55 # Boot Sector Signature