1 #------------------------------------------------------------------------------ 2 #* 3 #* Copyright (c) 2006 - 2007, Intel Corporation. All rights reserved.<BR> 4 #* This program and the accompanying materials 5 #* are licensed and made available under the terms and conditions of the BSD License 6 #* which accompanies this distribution. The full text of the license may be found at 7 #* http://opensource.org/licenses/bsd-license.php 8 #* 9 #* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, 10 #* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. 11 #* 12 #* bootsect.S 13 #* 14 #* bootsect.S is built as 16-bit binary file in 512 bytes and patched to disk/partition's 15 #* first section - boot sector. 16 #* 17 #* The startup sequence for DUET disk boot sector is: 18 #* 19 #* 1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget 20 #* whether disk/partition is bootable. 21 #* 2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and 22 #* hand off control to 0x7c00 code. 23 #* 3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file 24 #* and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist. 25 #* 4, boot sector load the first sector of EfiLdr binary which is start.com to 26 #* 0x2000:0x0000 address. 27 #* 5, boot sector handoff control to 0x2000:0x0000 for start.com binary. 28 #* 29 #------------------------------------------------------------------------------ 30 31 .stack: 32 .486p: 33 .code16 34 35 .equ FAT_DIRECTORY_ENTRY_SIZE, 0x020 36 .equ FAT_DIRECTORY_ENTRY_SHIFT, 5 37 .equ BLOCK_SIZE, 0x0200 38 .equ BLOCK_MASK, 0x01ff 39 .equ BLOCK_SHIFT, 9 40 # "EFILDR_____" 41 .equ LOADER_FILENAME_PART1, 0x04c494645 # "EFIL" 42 .equ LOADER_FILENAME_PART2, 0x020205244 # "DR__" 43 .equ LOADER_FILENAME_PART3, 0x020202020 # "____" 44 45 .org 0x0 46 .global _start 47 _start: 48 Ia32Jump: 49 jmp BootSectorEntryPoint # JMP inst - 3 bytes 50 nop 51 52 OemId: .ascii "INTEL " # OemId - 8 bytes 53 # BPB data below will be fixed by tool 54 SectorSize: .word 0 # Sector Size - 16 bits 55 SectorsPerCluster: .byte 0 # Sector Per Cluster - 8 bits 56 ReservedSectors: .word 0 # Reserved Sectors - 16 bits 57 NoFats: .byte 0 # Number of FATs - 8 bits 58 RootEntries: .word 0 # Root Entries - 16 bits 59 Sectors: .word 0 # Number of Sectors - 16 bits 60 Media: .byte 0 # Media - 8 bits - ignored 61 SectorsPerFat: .word 0 # Sectors Per FAT - 16 bits 62 SectorsPerTrack: .word 0 # Sectors Per Track - 16 bits - ignored 63 Heads: .word 0 # Heads - 16 bits - ignored 64 HiddenSectors: .long 0 # Hidden Sectors - 32 bits - ignored 65 LargeSectors: .long 0 # Large Sectors - 32 bits 66 PhysicalDrive: .byte 0 # PhysicalDriveNumber - 8 bits - ignored 67 CurrentHead: .byte 0 # Current Head - 8 bits 68 Signature: .byte 0 # Signature - 8 bits - ignored 69 VolId: .ascii " " # Volume Serial Number- 4 bytes 70 FatLabel: .ascii " " # Label - 11 bytes 71 SystemId: .ascii "FAT12 " # SystemId - 8 bytes 72 73 BootSectorEntryPoint: 74 #ASSUME ds:@code 75 #ASSUME ss:@code 76 77 # **************************************************************************** 78 # Start Print 79 # **************************************************************************** 80 movw $StartString, %si 81 call PrintString 82 83 # **************************************************************************** 84 # Print over 85 # **************************************************************************** 86 87 movw %cs, %ax # ax = 0 88 movw %ax, %ss # ss = 0 89 addw $0x1000, %ax 90 movw %ax, %ds 91 92 movw $0x7c00, %sp # sp = 0x7c00 93 movw %sp, %bp # bp = 0x7c00 94 95 movb $8, %ah # ah = 8 - Get Drive Parameters Function 96 movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL 97 int $0x13 # Get Drive Parameters 98 xorw %ax, %ax # ax = 0 99 movb %dh, %al # al = dh 100 incb %al # MaxHead = al + 1 101 pushw %ax # 0000:7bfe = MaxHead 102 movb %cl, %al # al = cl 103 andb $0x3f, %al # MaxSector = al & 0x3f 104 pushw %ax # 0000:7bfc = MaxSector 105 106 cmpw $0xaa55, SectorSignature(%bp) # Verify Boot Sector Signature 107 jne BadBootSector 108 movw RootEntries(%bp), %cx # cx = RootEntries 109 shlw $FAT_DIRECTORY_ENTRY_SHIFT, %cx # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes 110 movw %cx, %bx # bx = size of the Root Directory in bytes 111 andw $BLOCK_MASK, %bx # See if it is an even number of sectors long 112 jne BadBootSector # If is isn't, then the boot sector is bad. 113 movw %cx, %bx # bx = size of the Root Directory in bytes 114 shrw $BLOCK_SHIFT, %bx # bx = size of Root Directory in sectors 115 movb NoFats(%bp), %al # al = NoFats 116 xorb %ah, %ah # ah = 0 ==> ax = NoFats 117 mulw SectorsPerFat(%bp) # ax = NoFats * SectorsPerFat 118 addw ReservedSectors(%bp), %ax # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA 119 pushw %ds 120 popw %es 121 xorw %di, %di # Store directory in es:di = 1000:0000 122 call ReadBlocks # Read entire Root Directory 123 addw %bx, %ax # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector) 124 movw %ax, (%bp) # Save FirstClusterLBA (FirstDataSector) for later use 125 126 # dx - variable storage (initial value is 0) 127 # bx - loader (initial value is 0) 128 xorw %dx, %dx 129 xorw %bx, %bx 130 131 FindEFILDR: 132 cmpl $LOADER_FILENAME_PART1, (%di) # Compare to "EFIL" 133 jne FindVARSTORE 134 cmpl $LOADER_FILENAME_PART2, 4(%di) 135 jne FindVARSTORE 136 cmpl $LOADER_FILENAME_PART3, 7(%di) 137 jne FindVARSTORE 138 movw 26(%di), %bx # bx = Start Cluster for EFILDR <---------------------------------- 139 testw %dx, %dx 140 je FindNext # Efivar.bin is not loaded 141 jmp FoundAll 142 143 FindVARSTORE: 144 ## if the file is not loader file, see if it's "EFIVAR BIN" 145 cmpl $0x56494645, (%di) # Compare to "EFIV" 146 jne FindNext 147 cmpl $0x20205241, 4(%di) # Compare to "AR " 148 jne FindNext 149 cmpl $0x4e494220, 7(%di) # Compare to " BIN" 150 jne FindNext 151 movw %di, %dx # dx = Offset of Start Cluster for Efivar.bin <--------------------- 152 addw $26, %dx 153 testw %bx, %bx 154 je FindNext # Efildr is not loaded 155 jmp FoundAll 156 157 FindNext: 158 # go to next find 159 addw $FAT_DIRECTORY_ENTRY_SIZE, %di # Increment di 160 subw $FAT_DIRECTORY_ENTRY_SIZE, %cx # Decrement cx 161 # TODO: jump to FindVarStore if ... 162 jne FindEFILDR 163 jmp NotFoundAll 164 165 FoundAll: 166 FoundEFILDR: 167 movw %bx, %cx # cx = Start Cluster for EFILDR <---------------------------------- 168 movw %cs, %ax # Destination = 2000:0000 169 addw $0x2000, %ax 170 movw %ax, %es 171 xorw %di, %di 172 ReadFirstClusterOfEFILDR: 173 movw %cx, %ax # ax = StartCluster 174 subw $2, %ax # ax = StartCluster - 2 175 xorb %bh, %bh 176 movb SectorsPerCluster(%bp), %bl # bx = SectorsPerCluster 177 pushw %dx 178 mulw %bx 179 popw %dx # ax = (StartCluster - 2) * SectorsPerCluster 180 addw (%bp), %ax # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster 181 xorb %bh, %bh 182 movb SectorsPerCluster(%bp), %bl # bx = Number of Sectors in a cluster 183 pushw %es 184 call ReadBlocks 185 popw %ax 186 JumpIntoFirstSectorOfEFILDR: 187 movw %ax, JumpSegment(%bp) 188 JumpFarInstruction: 189 .byte 0xea 190 JumpOffset: 191 .word 0x000 192 JumpSegment: 193 .word 0x2000 194 195 196 PrintString: 197 movw $0xb800, %ax 198 movw %ax, %es 199 movw $0x7c0, %ax 200 movw %ax, %ds 201 movw $7, %cx 202 movw $160, %di 203 rep 204 movsw 205 ret 206 # **************************************************************************** 207 # ReadBlocks - Reads a set of blocks from a block device 208 # 209 # AX = Start LBA 210 # BX = Number of Blocks to Read 211 # ES:DI = Buffer to store sectors read from disk 212 # **************************************************************************** 213 214 # cx = Blocks 215 # bx = NumberOfBlocks 216 # si = StartLBA 217 218 ReadBlocks: 219 pusha 220 addl LBAOffsetForBootSector(%bp), %eax # Add LBAOffsetForBootSector to Start LBA 221 addl HiddenSectors(%bp), %eax # Add HiddenSectors to Start LBA 222 movl %eax, %esi # esi = Start LBA 223 movw %bx, %cx # cx = Number of blocks to read 224 ReadCylinderLoop: 225 movw $0x7bfc, %bp # bp = 0x7bfc 226 movl %esi, %eax # eax = Start LBA 227 xorl %edx, %edx # edx = 0 228 movzwl (%bp), %ebx # bx = MaxSector 229 divl %ebx # ax = StartLBA / MaxSector 230 incw %dx # dx = (StartLBA % MaxSector) + 1 231 subw %dx, %bx # bx = MaxSector - Sector 232 incw %bx # bx = MaxSector - Sector + 1 233 cmpw %bx, %cx # Compare (Blocks) to (MaxSector - Sector + 1) 234 jg LimitTransfer 235 movw %cx, %bx # bx = Blocks 236 LimitTransfer: 237 pushw %cx 238 movb %dl, %cl # cl = (StartLBA % MaxSector) + 1 = Sector 239 xorw %dx, %dx # dx = 0 240 divw 2(%bp) # ax = ax / (MaxHead + 1) = Cylinder 241 # dx = ax % (MaxHead + 1) = Head 242 243 pushw %bx # Save number of blocks to transfer 244 movb %dl, %dh # dh = Head 245 movw $0x7c00, %bp # bp = 0x7c00 246 movb PhysicalDrive(%bp), %dl # dl = Drive Number 247 movb %al, %ch # ch = Cylinder 248 movb %bl, %al # al = Blocks 249 movb $2, %ah # ah = Function 2 250 movw %di, %bx # es:bx = Buffer address 251 int $0x13 252 jc DiskError 253 popw %bx 254 popw %cx 255 movzwl %bx, %ebx 256 addl %ebx, %esi # StartLBA = StartLBA + NumberOfBlocks 257 subw %bx, %cx # Blocks = Blocks - NumberOfBlocks 258 movw %es, %ax 259 shlw $(BLOCK_SHIFT-4), %bx 260 addw %bx, %ax 261 movw %ax, %es # es:di = es:di + NumberOfBlocks*BLOCK_SIZE 262 cmpw $0, %cx 263 jne ReadCylinderLoop 264 popa 265 ret 266 267 # **************************************************************************** 268 # ERROR Condition: 269 # **************************************************************************** 270 NotFoundAll: 271 ## if we found EFILDR, continue 272 testw %bx, %bx 273 jne FoundEFILDR 274 BadBootSector: 275 DiskError: 276 movw $ErrorString, %si 277 call PrintString 278 Halt: 279 jmp Halt 280 281 StartString: 282 .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c 283 ErrorString: 284 .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c 285 286 # **************************************************************************** 287 # LBA Offset for BootSector, need patched by tool for HD boot. 288 # **************************************************************************** 289 290 .org 0x01fa # Comment it for pass build. Should optimise code size. 291 LBAOffsetForBootSector: 292 .long 0x0 293 294 # **************************************************************************** 295 # Sector Signature 296 # **************************************************************************** 297 298 .org 0x01fe # Comment it for pass build. 299 SectorSignature: 300 .word 0xaa55 # Boot Sector Signature 301 302 303 304
