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bootsect.S
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#------------------------------------------------------------------------------
#*
#* Copyright (c) 2006 - 2007, 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.
#*
#* bootsect.S
#*
#* bootsect.S is built as 16-bit binary file in 512 bytes and patched to disk/partition's
#* first section - boot sector.
#*
#* The startup sequence for DUET disk boot sector is:
#*
#* 1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget
#* whether disk/partition is bootable.
#* 2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and
#* hand off control to 0x7c00 code.
#* 3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file
#* and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist.
#* 4, boot sector load the first sector of EfiLdr binary which is start.com to
#* 0x2000:0x0000 address.
#* 5, boot sector handoff control to 0x2000:0x0000 for start.com binary.
#*
#------------------------------------------------------------------------------
.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