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 #* bs16.asm 13 #* 14 #* Abstract: 15 #* 16 #------------------------------------------------------------------------------ 17 18 #.MODEL small 19 .stack: 20 .486p: 21 .code16 22 23 .equ FAT_DIRECTORY_ENTRY_SIZE, 0x020 24 .equ FAT_DIRECTORY_ENTRY_SHIFT, 5 25 .equ BLOCK_SIZE, 0x0200 26 .equ BLOCK_MASK, 0x01ff 27 .equ BLOCK_SHIFT, 9 28 # "EFILDR_____" 29 .equ LOADER_FILENAME_PART1, 0x04c494645 # "EFIL" 30 .equ LOADER_FILENAME_PART2, 0x036315244 # "DR16" 31 .equ LOADER_FILENAME_PART3, 0x020202036 # "6___" 32 33 .org 0x0 34 .global _start 35 _start: 36 Ia32Jump: 37 jmp BootSectorEntryPoint # JMP inst - 3 bytes 38 nop 39 40 OemId: .ascii "INTEL " # OemId - 8 bytes 41 # BPB data below will be fixed by tool 42 SectorSize: .word 0 # Sector Size - 16 bits 43 SectorsPerCluster: .byte 0 # Sector Per Cluster - 8 bits 44 ReservedSectors: .word 0 # Reserved Sectors - 16 bits 45 NoFats: .byte 0 # Number of FATs - 8 bits 46 RootEntries: .word 0 # Root Entries - 16 bits 47 Sectors: .word 0 # Number of Sectors - 16 bits 48 Media: .byte 0 # Media - 8 bits - ignored 49 SectorsPerFat: .word 0 # Sectors Per FAT - 16 bits 50 SectorsPerTrack: .word 0 # Sectors Per Track - 16 bits - ignored 51 Heads: .word 0 # Heads - 16 bits - ignored 52 HiddenSectors: .long 0 # Hidden Sectors - 32 bits - ignored 53 LargeSectors: .long 0 # Large Sectors - 32 bits 54 PhysicalDrive: .byte 0 # PhysicalDriveNumber - 8 bits - ignored 55 CurrentHead: .byte 0 # Current Head - 8 bits 56 Signature: .byte 0 # Signature - 8 bits - ignored 57 VolId: .ascii " " # Volume Serial Number- 4 bytes 58 FatLabel: .ascii " " # Label - 11 bytes 59 SystemId: .ascii "FAT12 " # SystemId - 8 bytes 60 61 BootSectorEntryPoint: 62 #ASSUME ds:@code 63 #ASSUME ss:@code 64 65 # **************************************************************************** 66 # Start Print 67 # **************************************************************************** 68 movw $StartString, %si 69 call PrintString 70 71 # **************************************************************************** 72 # Print over 73 # **************************************************************************** 74 75 movw %cs, %ax # ax = 0 76 movw %ax, %ss # ss = 0 77 addw $0x1000, %ax 78 movw %ax, %ds 79 80 movw $0x7c00, %sp # sp = 0x7c00 81 movw %sp, %bp # bp = 0x7c00 82 83 movb $8, %ah # ah = 8 - Get Drive Parameters Function 84 movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL 85 int $0x13 # Get Drive Parameters 86 xorw %ax, %ax # ax = 0 87 movb %dh, %al # al = dh 88 incb %al # MaxHead = al + 1 89 pushw %ax # 0000:7bfe = MaxHead 90 movb %cl, %al # al = cl 91 andb $0x3f, %al # MaxSector = al & 0x3f 92 pushw %ax # 0000:7bfc = MaxSector 93 94 cmpw $0xaa55, SectorSignature(%bp) # Verify Boot Sector Signature 95 jne BadBootSector 96 movw RootEntries(%bp), %cx # cx = RootEntries 97 shlw $FAT_DIRECTORY_ENTRY_SHIFT, %cx # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes 98 movw %cx, %bx # bx = size of the Root Directory in bytes 99 andw $BLOCK_MASK, %bx # See if it is an even number of sectors long 100 jne BadBootSector # If is isn't, then the boot sector is bad. 101 movw %cx, %bx # bx = size of the Root Directory in bytes 102 shrw $BLOCK_SHIFT, %bx # bx = size of Root Directory in sectors 103 movb NoFats(%bp), %al # al = NoFats 104 xorb %ah, %ah # ah = 0 ==> ax = NoFats 105 mulw SectorsPerFat(%bp) # ax = NoFats * SectorsPerFat 106 addw ReservedSectors(%bp), %ax # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA 107 pushw %ds 108 popw %es 109 xorw %di, %di # Store directory in es:di = 1000:0000 110 call ReadBlocks # Read entire Root Directory 111 addw %bx, %ax # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector) 112 movw %ax, (%bp) # Save FirstClusterLBA (FirstDataSector) for later use 113 114 # dx - variable storage (initial value is 0) 115 # bx - loader (initial value is 0) 116 xorw %dx, %dx 117 xorw %bx, %bx 118 119 FindEFILDR: 120 cmpl $LOADER_FILENAME_PART1, (%di) # Compare to "EFIL" 121 jne FindVARSTORE 122 cmpl $LOADER_FILENAME_PART2, 4(%di) 123 jne FindVARSTORE 124 cmpl $LOADER_FILENAME_PART3, 7(%di) 125 jne FindVARSTORE 126 movw 26(%di), %bx # bx = Start Cluster for EFILDR <---------------------------------- 127 testw %dx, %dx 128 je FindNext # Efivar.bin is not loaded 129 jmp FoundAll 130 131 FindVARSTORE: 132 ##if the file is not loader file, see if it's "EFIVAR BIN" 133 cmpl $0x56494645, (%di) # Compare to "EFIV" 134 jne FindNext 135 cmpl $0x20205241, 4(%di) # Compare to "AR " 136 jne FindNext 137 cmpl $0x4e494220, 7(%di) # Compare to " BIN" 138 jne FindNext 139 movw %di, %dx # dx = Offset of Start Cluster for Efivar.bin <--------------------- 140 addw $26, %dx 141 testw %bx, %bx 142 je FindNext # Efildr is not loaded 143 jmp FoundAll 144 145 FindNext: 146 # go to next find 147 addw $FAT_DIRECTORY_ENTRY_SIZE, %di # Increment di 148 subw $FAT_DIRECTORY_ENTRY_SIZE, %cx # Decrement cx 149 # TODO: jump to FindVarStore if ... 150 jne FindEFILDR 151 jmp NotFoundAll 152 153 FoundAll: 154 FoundEFILDR: 155 movw %bx, %cx # cx = Start Cluster for EFILDR <---------------------------------- 156 movw %cs, %ax # Destination = 2000:0000 157 addw $0x2000, %ax 158 movw %ax, %es 159 xorw %di, %di 160 ReadFirstClusterOfEFILDR: 161 movw %cx, %ax # ax = StartCluster 162 subw $2, %ax # ax = StartCluster - 2 163 xorb %bh, %bh 164 movb SectorsPerCluster(%bp), %bl # bx = SectorsPerCluster 165 pushw %dx 166 mulw %bx 167 popw %dx # ax = (StartCluster - 2) * SectorsPerCluster 168 addw (%bp), %ax # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster 169 xorb %bh, %bh 170 movb SectorsPerCluster(%bp), %bl # bx = Number of Sectors in a cluster 171 pushw %es 172 call ReadBlocks 173 popw %ax 174 JumpIntoFirstSectorOfEFILDR: 175 movw %ax, JumpSegment(%bp) 176 JumpFarInstruction: 177 .byte 0xea 178 JumpOffset: 179 .word 0x000 180 JumpSegment: 181 .word 0x2000 182 183 184 PrintString: 185 movw $0xb800, %ax 186 movw %ax, %es 187 movw $0x7c0, %ax 188 movw %ax, %ds 189 movw $7, %cx 190 movw $160, %di 191 rep 192 movsw 193 ret 194 # **************************************************************************** 195 # ReadBlocks - Reads a set of blocks from a block device 196 # 197 # AX = Start LBA 198 # BX = Number of Blocks to Read 199 # ES:DI = Buffer to store sectors read from disk 200 # **************************************************************************** 201 202 # cx = Blocks 203 # bx = NumberOfBlocks 204 # si = StartLBA 205 206 ReadBlocks: 207 pusha 208 addl LBAOffsetForBootSector(%bp), %eax # Add LBAOffsetForBootSector to Start LBA 209 addl HiddenSectors(%bp), %eax # Add HiddenSectors to Start LBA 210 movl %eax, %esi # esi = Start LBA 211 movw %bx, %cx # cx = Number of blocks to read 212 ReadCylinderLoop: 213 movw $0x7bfc, %bp # bp = 0x7bfc 214 movl %esi, %eax # eax = Start LBA 215 xorl %edx, %edx # edx = 0 216 movzwl (%bp), %ebx # bx = MaxSector 217 divl %ebx # ax = StartLBA / MaxSector 218 incw %dx # dx = (StartLBA % MaxSector) + 1 219 subw %dx, %bx # bx = MaxSector - Sector 220 incw %bx # bx = MaxSector - Sector + 1 221 cmpw %bx, %cx # Compare (Blocks) to (MaxSector - Sector + 1) 222 jg LimitTransfer 223 movw %cx, %bx # bx = Blocks 224 LimitTransfer: 225 pushw %cx 226 movb %dl, %cl # cl = (StartLBA % MaxSector) + 1 = Sector 227 xorw %dx, %dx # dx = 0 228 divw 2(%bp) # ax = ax / (MaxHead + 1) = Cylinder 229 # dx = ax % (MaxHead + 1) = Head 230 231 pushw %bx # Save number of blocks to transfer 232 movb %dl, %dh # dh = Head 233 movw $0x7c00, %bp # bp = 0x7c00 234 movb PhysicalDrive(%bp), %dl # dl = Drive Number 235 movb %al, %ch # ch = Cylinder 236 movb %bl, %al # al = Blocks 237 movb $2, %ah # ah = Function 2 238 movw %di, %bx # es:bx = Buffer address 239 int $0x13 240 jc DiskError 241 popw %bx 242 popw %cx 243 movzwl %bx, %ebx 244 addl %ebx, %esi # StartLBA = StartLBA + NumberOfBlocks 245 subw %bx, %cx # Blocks = Blocks - NumberOfBlocks 246 movw %es, %ax 247 shlw $(BLOCK_SHIFT-4),%bx 248 addw %bx, %ax 249 movw %ax, %es # es:di = es:di + NumberOfBlocks*BLOCK_SIZE 250 cmpw $0, %cx 251 jne ReadCylinderLoop 252 popa 253 ret 254 255 # **************************************************************************** 256 # ERROR Condition: 257 # **************************************************************************** 258 NotFoundAll: 259 ## if we found EFILDR, continue 260 testw %bx, %bx 261 jne FoundEFILDR 262 BadBootSector: 263 DiskError: 264 movw $ErrorString, %si 265 call PrintString 266 Halt: 267 jmp Halt 268 269 StartString: 270 .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c 271 ErrorString: 272 .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c 273 274 # **************************************************************************** 275 # LBA Offset for BootSector, need patched by tool for HD boot. 276 # **************************************************************************** 277 278 .org 0x01fa 279 LBAOffsetForBootSector: 280 .long 0x0 281 282 # **************************************************************************** 283 # Sector Signature 284 # **************************************************************************** 285 286 .org 0x01fe 287 SectorSignature: 288 .word 0xaa55 # Boot Sector Signature 289 290 291 292
