1/* 2 * Copyright (c) 1998 Robert Nordier 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms are freely 6 * permitted provided that the above copyright notice and this 7 * paragraph and the following disclaimer are duplicated in all 8 * such forms. 9 * 10 * This software is provided "AS IS" and without any express or 11 * implied warranties, including, without limitation, the implied 12 * warranties of merchantability and fitness for a particular 13 * purpose. 14 */ 15 16/* Memory Locations */ 17 .set MEM_REL,0x700 # Relocation address 18 .set MEM_ARG,0x900 # Arguments 19 .set MEM_ORG,0x7c00 # Origin 20 .set MEM_BUF,0x8c00 # Load area 21 .set MEM_BTX,0x9000 # BTX start 22 .set MEM_JMP,0x9010 # BTX entry point 23 .set MEM_USR,0xa000 # Client start 24 .set BDA_BOOT,0x472 # Boot howto flag 25 26/* Partition Constants */ 27 .set PRT_OFF,0x1be # Partition offset 28 .set PRT_NUM,0x4 # Partitions 29 .set PRT_BSD,0xa5 # Partition type 30 31/* Flag Bits */ 32 .set FL_PACKET,0x80 # Packet mode 33 34/* Misc. Constants */ 35 .set SIZ_PAG,0x1000 # Page size 36 .set SIZ_SEC,0x200 # Sector size 37 38 .set NSECT,0x10 39 .globl start 40 .globl xread 41 .code16 42 43start: jmp main # Start recognizably 44 45/* 46 * This is the start of a standard BIOS Parameter Block (BPB). Most bootable 47 * FAT disks have this at the start of their MBR. While normal BIOS's will 48 * work fine without this section, IBM's El Torito emulation "fixes" up the 49 * BPB by writing into the memory copy of the MBR. Rather than have data 50 * written into our xread routine, we'll define a BPB to work around it. 51 * The data marked with (T) indicates a field required for a ThinkPad to 52 * recognize the disk and (W) indicates fields written from IBM BIOS code. 53 * The use of the BPB is based on what OpenBSD and NetBSD implemented in 54 * their boot code but the required fields were determined by trial and error. 55 * 56 * Note: If additional space is needed in boot1, one solution would be to 57 * move the "prompt" message data (below) to replace the OEM ID. 58 */ 59 .org 0x03, 0x00 60oemid: .space 0x08, 0x00 # OEM ID 61 62 .org 0x0b, 0x00 63bpb: .word 512 # sector size (T) 64 .byte 0 # sectors/clustor 65 .word 0 # reserved sectors 66 .byte 0 # number of FATs 67 .word 0 # root entries 68 .word 0 # small sectors 69 .byte 0 # media type (W) 70 .word 0 # sectors/fat 71 .word 18 # sectors per track (T) 72 .word 2 # number of heads (T) 73 .long 0 # hidden sectors (W) 74 .long 0 # large sectors 75 76 .org 0x24, 0x00 77ebpb: .byte 0 # BIOS physical drive number (W) 78 79 .org 0x25,0x90 80/* 81 * Trampoline used by boot2 to call read to read data from the disk via 82 * the BIOS. Call with: 83 * 84 * %cx:%ax - long - LBA to read in 85 * %es:(%bx) - caddr_t - buffer to read data into 86 * %dl - byte - drive to read from 87 * %dh - byte - num sectors to read 88 */ 89 90xread: push %ss # Address 91 pop %ds # data 92/* 93 * Setup an EDD disk packet and pass it to read 94 */ 95xread.1: # Starting 96 pushl $0x0 # absolute 97 push %cx # block 98 push %ax # number 99 push %es # Address of 100 push %bx # transfer buffer 101 xor %ax,%ax # Number of 102 movb %dh,%al # blocks to 103 push %ax # transfer 104 push $0x10 # Size of packet 105 mov %sp,%bp # Packet pointer 106 callw read # Read from disk 107 lea 0x10(%bp),%sp # Clear stack 108 lret # To far caller 109/* 110 * Load the rest of boot2 and BTX up, copy the parts to the right locations, 111 * and start it all up. 112 */ 113 114/* 115 * Setup the segment registers to flat addressing (segment 0) and setup the 116 * stack to end just below the start of our code. 117 */ 118main: cld # String ops inc 119 xor %cx,%cx # Zero 120 mov %cx,%es # Address 121 mov %cx,%ds # data 122 mov %cx,%ss # Set up 123 mov $start,%sp # stack 124/* 125 * Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets 126 * %cx == 0x100. Note that boot1 does not use this relocated copy 127 * of itself while loading boot2; however, BTX reclaims the memory 128 * used by boot1 during its initialization. As a result, boot2 uses 129 * xread from the relocated copy. 130 */ 131 mov %sp,%si # Source 132 mov $MEM_REL,%di # Destination 133 incb %ch # Word count 134 rep # Copy 135 movsw # code 136/* 137 * If we are on a hard drive, then load the MBR and look for the first 138 * FreeBSD slice. We use the fake partition entry below that points to 139 * the MBR when we call nread. The first pass looks for the first active 140 * FreeBSD slice. The second pass looks for the first non-active FreeBSD 141 * slice if the first one fails. 142 */ 143 mov $part4,%si # Partition 144 cmpb $0x80,%dl # Hard drive? 145 jb main.4 # No 146 movb $0x1,%dh # Block count 147 callw nread # Read MBR 148 mov $0x1,%cx # Two passes 149main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table 150 movb $0x1,%dh # Partition 151main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type? 152 jne main.3 # No 153 jcxz main.5 # If second pass 154 testb $0x80,(%si) # Active? 155 jnz main.5 # Yes 156main.3: add $0x10,%si # Next entry 157 incb %dh # Partition 158 cmpb $0x1+PRT_NUM,%dh # In table? 159 jb main.2 # Yes 160 dec %cx # Do two 161 jcxz main.1 # passes 162/* 163 * If we get here, we didn't find any FreeBSD slices at all, so print an 164 * error message and die. 165 */ 166 mov $msg_part,%si # Message 167 jmp error # Error 168/* 169 * Floppies use partition 0 of drive 0. 170 */ 171main.4: xor %dx,%dx # Partition:drive 172/* 173 * Ok, we have a slice and drive in %dx now, so use that to locate and load 174 * boot2. %si references the start of the slice we are looking for, so go 175 * ahead and load up the first 16 sectors (boot1 + boot2) from that. When 176 * we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus, 177 * boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00. 178 * The first part of boot2 is the disklabel, which is 0x200 bytes long. 179 * The second part is BTX, which is thus loaded into 0x9000, which is where 180 * it also runs from. The boot2.bin binary starts right after the end of 181 * BTX, so we have to figure out where the start of it is and then move the 182 * binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but 183 * when we use btxld to create boot2, we use an entry point of 0x2000. That 184 * entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000. 185 */ 186main.5: mov %dx,MEM_ARG # Save args 187 movb $NSECT,%dh # Sector count 188 callw nread # Read disk 189 mov $MEM_BTX,%bx # BTX 190 mov 0xa(%bx),%si # Get BTX length and set 191 add %bx,%si # %si to start of boot2.bin 192 mov $MEM_USR+SIZ_PAG*2,%di # Client page 2 193 mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx # Byte 194 sub %si,%cx # count 195 rep # Relocate 196 movsb # client 197 198/* 199 * Enable A20 so we can access memory above 1 meg. 200 * Use the zero-valued %cx as a timeout for embedded hardware which do not 201 * have a keyboard controller. 202 */ 203seta20: cli # Disable interrupts 204seta20.1: dec %cx # Timeout? 205 jz seta20.3 # Yes 206 inb $0x64,%al # Get status 207 testb $0x2,%al # Busy? 208 jnz seta20.1 # Yes 209 movb $0xd1,%al # Command: Write 210 outb %al,$0x64 # output port 211seta20.2: inb $0x64,%al # Get status 212 testb $0x2,%al # Busy? 213 jnz seta20.2 # Yes 214 movb $0xdf,%al # Enable 215 outb %al,$0x60 # A20 216seta20.3: sti # Enable interrupts 217 218 jmp start+MEM_JMP-MEM_ORG # Start BTX 219 220 221/* 222 * Trampoline used to call read from within boot1. 223 */ 224nread: mov $MEM_BUF,%bx # Transfer buffer 225 mov 0x8(%si),%ax # Get 226 mov 0xa(%si),%cx # LBA 227 push %cs # Read from 228 callw xread.1 # disk 229 jnc return # If success, return 230 mov $msg_read,%si # Otherwise, set the error 231 # message and fall through to 232 # the error routine 233/* 234 * Print out the error message pointed to by %ds:(%si) followed 235 * by a prompt, wait for a keypress, and then reboot the machine. 236 */ 237error: callw putstr # Display message 238 mov $prompt,%si # Display 239 callw putstr # prompt 240 xorb %ah,%ah # BIOS: Get 241 int $0x16 # keypress 242 movw $0x1234, BDA_BOOT # Do a warm boot 243 ljmp $0xf000,$0xfff0 # reboot the machine 244/* 245 * Display a null-terminated string using the BIOS output. 246 */ 247putstr.0: mov $0x7,%bx # Page:attribute 248 movb $0xe,%ah # BIOS: Display 249 int $0x10 # character 250putstr: lodsb # Get char 251 testb %al,%al # End of string? 252 jne putstr.0 # No 253 254/* 255 * Overused return code. ereturn is used to return an error from the 256 * read function. Since we assume putstr succeeds, we (ab)use the 257 * same code when we return from putstr. 258 */ 259ereturn: movb $0x1,%ah # Invalid 260 stc # argument 261return: retw # To caller 262/* 263 * Reads sectors from the disk. If EDD is enabled, then check if it is 264 * installed and use it if it is. If it is not installed or not enabled, then 265 * fall back to using CHS. Since we use a LBA, if we are using CHS, we have to 266 * fetch the drive parameters from the BIOS and divide it out ourselves. 267 * Call with: 268 * 269 * %dl - byte - drive number 270 * stack - 10 bytes - EDD Packet 271 */ 272read: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled? 273 jz read.1 # No, use CHS 274 cmpb $0x80,%dl # Hard drive? 275 jb read.1 # No, use CHS 276 mov $0x55aa,%bx # Magic 277 push %dx # Save 278 movb $0x41,%ah # BIOS: Check 279 int $0x13 # extensions present 280 pop %dx # Restore 281 jc read.1 # If error, use CHS 282 cmp $0xaa55,%bx # Magic? 283 jne read.1 # No, so use CHS 284 testb $0x1,%cl # Packet interface? 285 jz read.1 # No, so use CHS 286 mov %bp,%si # Disk packet 287 movb $0x42,%ah # BIOS: Extended 288 int $0x13 # read 289 retw # To caller 290read.1: push %dx # Save 291 movb $0x8,%ah # BIOS: Get drive 292 int $0x13 # parameters 293 movb %dh,%ch # Max head number 294 pop %dx # Restore 295 jc return # If error 296 andb $0x3f,%cl # Sectors per track 297 jz ereturn # If zero 298 cli # Disable interrupts 299 mov 0x8(%bp),%eax # Get LBA 300 push %dx # Save 301 movzbl %cl,%ebx # Divide by 302 xor %edx,%edx # sectors 303 div %ebx # per track 304 movb %ch,%bl # Max head number 305 movb %dl,%ch # Sector number 306 inc %bx # Divide by 307 xorb %dl,%dl # number 308 div %ebx # of heads 309 movb %dl,%bh # Head number 310 pop %dx # Restore 311 cmpl $0x3ff,%eax # Cylinder number supportable? 312 sti # Enable interrupts 313 ja ereturn # No, return an error 314 xchgb %al,%ah # Set up cylinder 315 rorb $0x2,%al # number 316 orb %ch,%al # Merge 317 inc %ax # sector 318 xchg %ax,%cx # number 319 movb %bh,%dh # Head number 320 subb %ah,%al # Sectors this track 321 mov 0x2(%bp),%ah # Blocks to read 322 cmpb %ah,%al # To read 323 jb read.2 # this 324#ifdef TRACK_AT_A_TIME 325 movb %ah,%al # track 326#else 327 movb $1,%al # one sector 328#endif 329read.2: mov $0x5,%di # Try count 330read.3: les 0x4(%bp),%bx # Transfer buffer 331 push %ax # Save 332 movb $0x2,%ah # BIOS: Read 333 int $0x13 # from disk 334 pop %bx # Restore 335 jnc read.4 # If success 336 dec %di # Retry? 337 jz read.6 # No 338 xorb %ah,%ah # BIOS: Reset 339 int $0x13 # disk system 340 xchg %bx,%ax # Block count 341 jmp read.3 # Continue 342read.4: movzbw %bl,%ax # Sectors read 343 add %ax,0x8(%bp) # Adjust 344 jnc read.5 # LBA, 345 incw 0xa(%bp) # transfer 346read.5: shlb %bl # buffer 347 add %bl,0x5(%bp) # pointer, 348 sub %al,0x2(%bp) # block count 349 ja read.1 # If not done 350read.6: retw # To caller 351 352/* Messages */ 353 354msg_read: .asciz "Read" 355msg_part: .asciz "Boot" 356 357prompt: .asciz " error\r\n" 358 359flags: .byte FLAGS # Flags 360 361 .org PRT_OFF,0x90 362 363/* Partition table */ 364 365 .fill 0x30,0x1,0x0 366part4: .byte 0x80, 0x00, 0x01, 0x00 367 .byte 0xa5, 0xfe, 0xff, 0xff 368 .byte 0x00, 0x00, 0x00, 0x00 369 .byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh 370 371 .word 0xaa55 # Magic number 372