boot1.S revision 134430
1116742Ssam/* 2116904Ssam * Copyright (c) 1998 Robert Nordier 3186904Ssam * All rights reserved. 4116742Ssam * 5116742Ssam * Redistribution and use in source and binary forms are freely 6116742Ssam * permitted provided that the above copyright notice and this 7116742Ssam * paragraph and the following disclaimer are duplicated in all 8116742Ssam * such forms. 9116742Ssam * 10116742Ssam * This software is provided "AS IS" and without any express or 11116742Ssam * implied warranties, including, without limitation, the implied 12116742Ssam * warranties of merchantability and fitness for a particular 13116742Ssam * purpose. 14116742Ssam * 15116904Ssam * $FreeBSD: head/sys/boot/i386/boot2/boot1.S 134430 2004-08-28 08:32:23Z yar $ 16116904Ssam */ 17116904Ssam 18116904Ssam/* Memory Locations */ 19116904Ssam .set MEM_REL,0x700 # Relocation address 20116904Ssam .set MEM_ARG,0x900 # Arguments 21116904Ssam .set MEM_ORG,0x7c00 # Origin 22116904Ssam .set MEM_BUF,0x8cec # Load area 23116904Ssam .set MEM_BTX,0x9000 # BTX start 24116904Ssam .set MEM_JMP,0x9010 # BTX entry point 25116904Ssam .set MEM_USR,0xa000 # Client start 26116742Ssam .set BDA_BOOT,0x472 # Boot howto flag 27116742Ssam 28116742Ssam/* Partition Constants */ 29116742Ssam .set PRT_OFF,0x1be # Partition offset 30116742Ssam .set PRT_NUM,0x4 # Partitions 31138568Ssam .set PRT_BSD,0xa5 # Partition type 32170530Ssam 33116742Ssam/* Flag Bits */ 34138568Ssam .set FL_PACKET,0x80 # Packet mode 35178354Ssam 36178354Ssam/* Misc. Constants */ 37178354Ssam .set SIZ_PAG,0x1000 # Page size 38178354Ssam .set SIZ_SEC,0x200 # Sector size 39178354Ssam 40178354Ssam .set NSECT,0x10 41178354Ssam .globl start 42178354Ssam .globl xread 43178354Ssam .code16 44178354Ssam 45138568Ssamstart: jmp main # Start recognizably 46138568Ssam 47138568Ssam/* 48138568Ssam * This is the start of a standard BIOS Parameter Block (BPB). Most bootable 49138568Ssam * FAT disks have this at the start of their MBR. While normal BIOS's will 50138568Ssam * work fine without this section, IBM's El Torito emulation "fixes" up the 51138568Ssam * BPB by writing into the memory copy of the MBR. Rather than have data 52138568Ssam * written into our xread routine, we'll define a BPB to work around it. 53138568Ssam * The data marked with (T) indicates a field required for a ThinkPad to 54170530Ssam * recognize the disk and (W) indicates fields written from IBM BIOS code. 55138568Ssam * The use of the BPB is based on what OpenBSD and NetBSD implemented in 56172211Ssam * their boot code but the required fields were determined by trial and error. 57172211Ssam * 58172211Ssam * Note: If additional space is needed in boot1, one solution would be to 59116742Ssam * move the "prompt" message data (below) to replace the OEM ID. 60116742Ssam */ 61116742Ssam .org 0x03, 0x00 62170530Ssamoemid: .space 0x08, 0x00 # OEM ID 63138568Ssam 64116742Ssam .org 0x0b, 0x00 65138568Ssambpb: .word 512 # sector size (T) 66138568Ssam .byte 0 # sectors/clustor 67178354Ssam .word 0 # reserved sectors 68138568Ssam .byte 0 # number of FATs 69116742Ssam .word 0 # root entries 70178354Ssam .word 0 # small sectors 71178354Ssam .byte 0 # media type (W) 72190093Srpaulo .word 0 # sectors/fat 73178354Ssam .word 18 # sectors per track (T) 74178354Ssam .word 2 # number of heads (T) 75178354Ssam .long 0 # hidden sectors (W) 76178354Ssam .long 0 # large sectors 77178354Ssam 78178354Ssam .org 0x24, 0x00 79178354Ssamebpb: .byte 0 # BIOS physical drive number (W) 80178354Ssam 81178354Ssam .org 0x25,0x90 82178354Ssam/* 83186904Ssam * Trampoline used by boot2 to call read to read data from the disk via 84193239Ssam * the BIOS. Call with: 85178354Ssam * 86178354Ssam * %cx:%ax - long - LBA to read in 87178354Ssam * %es:(%bx) - caddr_t - buffer to read data into 88178354Ssam * %dl - byte - drive to read from 89178354Ssam * %dh - byte - num sectors to read 90178354Ssam */ 91116742Ssam 92116742Ssamxread: push %ss # Address 93116742Ssam pop %ds # data 94116742Ssam/* 95116742Ssam * Setup an EDD disk packet and pass it to read 96116742Ssam */ 97178354Ssamxread.1: # Starting 98178354Ssam pushl $0x0 # absolute 99178354Ssam push %cx # block 100178354Ssam push %ax # number 101178354Ssam push %es # Address of 102178354Ssam push %bx # transfer buffer 103120483Ssam xor %ax,%ax # Number of 104183252Ssam movb %dh,%al # blocks to 105183252Ssam push %ax # transfer 106183252Ssam push $0x10 # Size of packet 107183252Ssam mov %sp,%bp # Packet pointer 108183252Ssam callw read # Read from disk 109183252Ssam lea 0x10(%bp),%sp # Clear stack 110183252Ssam lret # To far caller 111183252Ssam/* 112183252Ssam * Load the rest of boot2 and BTX up, copy the parts to the right locations, 113183252Ssam * and start it all up. 114183252Ssam */ 115183252Ssam 116183252Ssam/* 117183255Ssam * Setup the segment registers to flat addressing (segment 0) and setup the 118183255Ssam * stack to end just below the start of our code. 119183256Ssam */ 120183257Ssammain: cld # String ops inc 121183257Ssam xor %cx,%cx # Zero 122186099Ssam mov %cx,%es # Address 123193549Ssam mov %cx,%ds # data 124193549Ssam mov %cx,%ss # Set up 125183252Ssam mov $start,%sp # stack 126183252Ssam/* 127183252Ssam * Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets 128170530Ssam * %cx == 0x100. 129170530Ssam */ 130170530Ssam mov %sp,%si # Source 131170530Ssam mov $MEM_REL,%di # Destination 132170530Ssam incb %ch # Word count 133170530Ssam rep # Copy 134170530Ssam movsw # code 135170530Ssam/* 136183252Ssam * If we are on a hard drive, then load the MBR and look for the first 137170530Ssam * FreeBSD slice. We use the fake partition entry below that points to 138183251Ssam * the MBR when we call nread. The first pass looks for the first active 139173273Ssam * FreeBSD slice. The second pass looks for the first non-active FreeBSD 140170530Ssam * slice if the first one fails. 141178354Ssam */ 142172225Ssam mov $part4,%si # Partition 143191756Ssam cmpb $0x80,%dl # Hard drive? 144172225Ssam jb main.4 # No 145191756Ssam movb $0x1,%dh # Block count 146170530Ssam callw nread # Read MBR 147138568Ssam mov $0x1,%cx # Two passes 148138568Ssammain.1: mov $MEM_BUF+PRT_OFF,%si # Partition table 149116742Ssam movb $0x1,%dh # Partition 150116742Ssammain.2: cmpb $PRT_BSD,0x4(%si) # Our partition type? 151178354Ssam jne main.3 # No 152170530Ssam jcxz main.5 # If second pass 153116742Ssam testb $0x80,(%si) # Active? 154116742Ssam jnz main.5 # Yes 155170530Ssammain.3: add $0x10,%si # Next entry 156170530Ssam incb %dh # Partition 157116742Ssam cmpb $0x1+PRT_NUM,%dh # In table? 158116742Ssam jb main.2 # Yes 159138568Ssam dec %cx # Do two 160170530Ssam jcxz main.1 # passes 161178354Ssam/* 162138568Ssam * If we get here, we didn't find any FreeBSD slices at all, so print an 163170530Ssam * error message and die. 164170530Ssam */ 165170530Ssam mov $msg_part,%si # Message 166170530Ssam jmp error # Error 167116742Ssam/* 168170530Ssam * Floppies use partition 0 of drive 0. 169170530Ssam */ 170170530Ssammain.4: xor %dx,%dx # Partition:drive 171178354Ssam/* 172170530Ssam * Ok, we have a slice and drive in %dx now, so use that to locate and load 173170530Ssam * boot2. %si references the start of the slice we are looking for, so go 174170530Ssam * ahead and load up the first 16 sectors (boot1 + boot2) from that. When 175116742Ssam * we read it in, we conveniently use 0x8cec as our transfer buffer. Thus, 176170530Ssam * boot1 ends up at 0x8cec, and boot2 starts at 0x8cec + 0x200 = 0x8eec. 177170530Ssam * The first part of boot2 is the disklabel, which is 0x114 bytes long. 178170530Ssam * The second part is BTX, which is thus loaded into 0x9000, which is where 179170530Ssam * it also runs from. The boot2.bin binary starts right after the end of 180170530Ssam * BTX, so we have to figure out where the start of it is and then move the 181170530Ssam * binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but 182170530Ssam * when we use btxld to create boot2, we use an entry point of 0x2000. That 183170530Ssam * entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000. 184170530Ssam */ 185170530Ssammain.5: mov %dx,MEM_ARG # Save args 186170530Ssam movb $NSECT,%dh # Sector count 187170530Ssam callw nread # Read disk 188116742Ssam mov $MEM_BTX,%bx # BTX 189138568Ssam mov 0xa(%bx),%si # Get BTX length and set 190138568Ssam add %bx,%si # %si to start of boot2.bin 191178354Ssam mov $MEM_USR+SIZ_PAG*2,%di # Client page 2 192184288Ssam mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx # Byte 193138568Ssam sub %si,%cx # count 194178354Ssam rep # Relocate 195178354Ssam movsb # client 196178354Ssam 197178354Ssam/* 198193239Ssam * Enable A20 so we can access memory above 1 meg. 199116742Ssam * Use the zero-valued %cx as a timeout for embedded hardware which do not 200138568Ssam * have a keyboard controller. 201178354Ssam */ 202116742Ssamseta20: cli # Disable interrupts 203170530Ssamseta20.1: dec %cx # Timeout? 204173273Ssam jz seta20.3 # Yes 205173273Ssam inb $0x64,%al # Get status 206193549Ssam testb $0x2,%al # Busy? 207193549Ssam jnz seta20.1 # Yes 208182828Ssam movb $0xd1,%al # Command: Write 209182828Ssam outb %al,$0x64 # output port 210193549Ssamseta20.2: inb $0x64,%al # Get status 211193549Ssam testb $0x2,%al # Busy? 212193549Ssam jnz seta20.2 # Yes 213170530Ssam movb $0xdf,%al # Enable 214187797Ssam outb %al,$0x60 # A20 215187797Ssamseta20.3: 216187797Ssam sti # Enable interrupts 217187797Ssam 218187797Ssam jmp start+MEM_JMP-MEM_ORG # Start BTX 219138568Ssam 220138568Ssam 221138568Ssam/* 222138568Ssam * Trampoline used to call read from within boot1. 223138568Ssam */ 224138568Ssamnread: mov $MEM_BUF,%bx # Transfer buffer 225178354Ssam mov 0x8(%si),%ax # Get 226178354Ssam mov 0xa(%si),%cx # LBA 227178354Ssam push %cs # Read from 228178354Ssam callw xread.1 # disk 229178354Ssam jnc return # If success, return 230178354Ssam mov $msg_read,%si # Otherwise, set the error 231178354Ssam # message and fall through to 232178354Ssam # the error routine 233178354Ssam/* 234178354Ssam * Print out the error message pointed to by %ds:(%si) followed 235178354Ssam * by a prompt, wait for a keypress, and then reboot the machine. 236178354Ssam */ 237178354Ssamerror: callw putstr # Display message 238178354Ssam mov $prompt,%si # Display 239178354Ssam callw putstr # prompt 240178354Ssam xorb %ah,%ah # BIOS: Get 241178354Ssam int $0x16 # keypress 242178354Ssam movw $0x1234, BDA_BOOT # Do a warm boot 243178354Ssam ljmp $0xffff,$0x0 # reboot the machine 244178354Ssam/* 245178354Ssam * Display a null-terminated string using the BIOS output. 246178354Ssam */ 247178354Ssamputstr.0: mov $0x7,%bx # Page:attribute 248178354Ssam movb $0xe,%ah # BIOS: Display 249178354Ssam int $0x10 # character 250178354Ssamputstr: lodsb # Get char 251178354Ssam testb %al,%al # End of string? 252178354Ssam jne putstr.0 # No 253178354Ssam 254178354Ssam/* 255178354Ssam * Overused return code. ereturn is used to return an error from the 256178354Ssam * read function. Since we assume putstr succeeds, we (ab)use the 257116742Ssam * same code when we return from putstr. 258116742Ssam */ 259116742Ssamereturn: movb $0x1,%ah # Invalid 260138568Ssam stc # argument 261116742Ssamreturn: retw # To caller 262116742Ssam/* 263116742Ssam * Reads sectors from the disk. If EDD is enabled, then check if it is 264116742Ssam * installed and use it if it is. If it is not installed or not enabled, then 265116742Ssam * fall back to using CHS. Since we use a LBA, if we are using CHS, we have to 266116742Ssam * fetch the drive parameters from the BIOS and divide it out ourselves. 267138568Ssam * Call with: 268116742Ssam * 269116742Ssam * %dl - byte - drive number 270116742Ssam * stack - 10 bytes - EDD Packet 271116742Ssam */ 272116742Ssamread: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled? 273144618Ssam jz read.1 # No, use CHS 274144618Ssam cmpb $0x80,%dl # Hard drive? 275144618Ssam jb read.1 # No, use CHS 276178354Ssam mov $0x55aa,%bx # Magic 277178354Ssam push %dx # Save 278178354Ssam movb $0x41,%ah # BIOS: Check 279127877Ssam int $0x13 # extensions present 280138568Ssam pop %dx # Restore 281138568Ssam jc read.1 # If error, use CHS 282138568Ssam cmp $0xaa55,%bx # Magic? 283138568Ssam jne read.1 # No, so use CHS 284138568Ssam testb $0x1,%cl # Packet interface? 285116742Ssam jz read.1 # No, so use CHS 286148302Ssam mov %bp,%si # Disk packet 287148302Ssam movb $0x42,%ah # BIOS: Extended 288138568Ssam int $0x13 # read 289178354Ssam retw # To caller 290178354Ssamread.1: push %dx # Save 291178354Ssam movb $0x8,%ah # BIOS: Get drive 292178354Ssam int $0x13 # parameters 293178354Ssam movb %dh,%ch # Max head number 294191746Sthompsa pop %dx # Restore 295191746Sthompsa jc return # If error 296178354Ssam andb $0x3f,%cl # Sectors per track 297148306Ssam jz ereturn # If zero 298170530Ssam cli # Disable interrupts 299184274Ssam mov 0x8(%bp),%eax # Get LBA 300170530Ssam push %dx # Save 301178354Ssam movzbl %cl,%ebx # Divide by 302178354Ssam xor %edx,%edx # sectors 303138568Ssam div %ebx # per track 304178354Ssam movb %ch,%bl # Max head number 305178354Ssam movb %dl,%ch # Sector number 306178354Ssam inc %bx # Divide by 307178354Ssam xorb %dl,%dl # number 308178354Ssam div %ebx # of heads 309178354Ssam movb %dl,%bh # Head number 310178354Ssam pop %dx # Restore 311138568Ssam cmpl $0x3ff,%eax # Cylinder number supportable? 312138568Ssam sti # Enable interrupts 313178354Ssam ja ereturn # No, return an error 314178354Ssam xchgb %al,%ah # Set up cylinder 315178354Ssam rorb $0x2,%al # number 316178354Ssam orb %ch,%al # Merge 317138568Ssam inc %ax # sector 318138568Ssam xchg %ax,%cx # number 319138568Ssam movb %bh,%dh # Head number 320138568Ssam subb %ah,%al # Sectors this track 321138568Ssam mov 0x2(%bp),%ah # Blocks to read 322138568Ssam cmpb %ah,%al # To read 323170530Ssam jb read.2 # this 324170530Ssam#ifdef TRACK_AT_A_TIME 325178354Ssam movb %ah,%al # track 326138568Ssam#else 327178354Ssam movb $1,%al # one sector 328138568Ssam#endif 329138568Ssamread.2: mov $0x5,%di # Try count 330138568Ssamread.3: les 0x4(%bp),%bx # Transfer buffer 331178354Ssam push %ax # Save 332178354Ssam movb $0x2,%ah # BIOS: Read 333178354Ssam int $0x13 # from disk 334178354Ssam pop %bx # Restore 335178354Ssam jnc read.4 # If success 336178354Ssam dec %di # Retry? 337178354Ssam jz read.6 # No 338178354Ssam xorb %ah,%ah # BIOS: Reset 339178354Ssam int $0x13 # disk system 340178354Ssam xchg %bx,%ax # Block count 341138568Ssam jmp read.3 # Continue 342144618Ssamread.4: movzbw %bl,%ax # Sectors read 343138568Ssam add %ax,0x8(%bp) # Adjust 344178354Ssam jnc read.5 # LBA, 345178354Ssam incw 0xa(%bp) # transfer 346178354Ssamread.5: shlb %bl # buffer 347178354Ssam add %bl,0x5(%bp) # pointer, 348170530Ssam sub %al,0x2(%bp) # block count 349178354Ssam ja read.1 # If not done 350138568Ssamread.6: retw # To caller 351178354Ssam 352178354Ssam/* Messages */ 353178354Ssam 354178354Ssammsg_read: .asciz "Read" 355178354Ssammsg_part: .asciz "Boot" 356178354Ssam 357178354Ssamprompt: .asciz " error\r\n" 358178354Ssam 359178354Ssamflags: .byte FLAGS # Flags 360178354Ssam 361170530Ssam .org PRT_OFF,0x90 362170530Ssam 363138568Ssam/* Partition table */ 364148863Ssam 365148863Ssam .fill 0x30,0x1,0x0 366170530Ssampart4: .byte 0x80, 0x00, 0x01, 0x00 367148863Ssam .byte 0xa5, 0xfe, 0xff, 0xff 368178354Ssam .byte 0x00, 0x00, 0x00, 0x00 369170530Ssam .byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh 370170530Ssam 371138568Ssam .word 0xaa55 # Magic number 372138568Ssam