boot1.S revision 50477
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# $FreeBSD: head/sys/boot/i386/boot2/boot1.S 50477 1999-08-28 01:08:13Z peter $ 17 18 .set MEM_REL,0x700 # Relocation address 19 .set MEM_ARG,0x900 # Arguments 20 .set MEM_ORG,0x7c00 # Origin 21 .set MEM_BUF,0x8c00 # Load area 22 .set MEM_BTX,0x9000 # BTX start 23 .set MEM_JMP,0x9010 # BTX entry point 24 .set MEM_USR,0xa000 # Client start 25 26 .set PRT_OFF,0x1be # Partition offset 27 .set PRT_NUM,0x4 # Partitions 28 .set PRT_BSD,0xa5 # Partition type 29 30 .set SIZ_PAG,0x1000 # Page size 31 .set SIZ_SEC,0x200 # Sector size 32 33 .globl start 34 .globl xread 35 36start: jmp main # Start recognizably 37 38 .org 0x4,0x90 39 40# External read from disk 41 42xread: pushl %ss # Address 43 popl %ds # data 44xread.1: o16 # Starting 45 pushb $0x0 # absolute 46 pushl %ecx # block 47 pushl %eax # number 48 pushl %es # Address of 49 pushl %ebx # transfer buffer 50 xorl %eax,%eax # Number of 51 movb %dh,%al # blocks to 52 pushl %eax # transfer 53 pushb $0x10 # Size of packet 54 movl %esp,%ebp # Packet pointer 55 callwi(read) # Read from disk 56 leaw1r(0x10,_bp_,_sp) # Clear stack 57 lret # To far caller 58 59# Bootstrap 60 61main: cld # String ops inc 62 xorl %ecx,%ecx # Zero 63 movl %cx,%es # Address 64 movl %cx,%ds # data 65 movl %cx,%ss # Set up 66 movwir(start,_sp) # stack 67 movl %esp,%esi # Source 68 movwir(MEM_REL,_di) # Destination 69 incb %ch # Word count 70 rep # Copy 71 movsl # code 72 movwir(part4,_si) # Partition 73 cmpb $0x80,%dl # Hard drive? 74 jb main.4 # No 75 movb $0x1,%dh # Block count 76 callwi(nread) # Read MBR 77 movwir(0x1,_cx) # Two passes 78main.1: movwir(MEM_BUF+PRT_OFF,_si) # Partition table 79 movb $0x1,%dh # Partition 80main.2: cmpbi1(PRT_BSD,0x4,_si_) # Our partition type? 81 jne main.3 # No 82 jecxz main.5 # If second pass 83 tstbi0(0x80,_si_) # Active? 84 jnz main.5 # Yes 85main.3: addl $0x10,%esi # Next entry 86 incb %dh # Partition 87 cmpb $0x1+PRT_NUM,%dh # In table? 88 jb main.2 # Yes 89 decl %ecx # Do two 90 jecxz main.1 # passes 91 movwir(msg_part,_si) # Message 92 jmp error # Error 93main.4: xorl %edx,%edx # Partition:drive 94main.5: movwrm(_dx,MEM_ARG) # Save args 95 movb $0x10,%dh # Sector count 96 callwi(nread) # Read disk 97 movwir(MEM_BTX,_bx) # BTX 98 movw1r(0xa,_bx_,_si) # Point past 99 addl %ebx,%esi # it 100 movwir(MEM_USR+SIZ_PAG,_di) # Client page 1 101 movwir(MEM_BTX+0xe*SIZ_SEC,_cx) # Byte 102 subl %esi,%ecx # count 103 rep # Relocate 104 movsb # client 105 subl %edi,%ecx # Byte count 106 xorb %al,%al # Zero 107 rep # assumed 108 stosb # bss 109 callwi(seta20) # Enable A20 110 jmpnwi(start+MEM_JMP-MEM_ORG) # Start BTX 111 112# Enable A20 113 114seta20: cli # Disable interrupts 115seta20.1: inb $0x64,%al # Get status 116 testb $0x2,%al # Busy? 117 jnz seta20.1 # Yes 118 movb $0xd1,%al # Command: Write 119 outb %al,$0x64 # output port 120seta20.2: inb $0x64,%al # Get status 121 testb $0x2,%al # Busy? 122 jnz seta20.2 # Yes 123 movb $0xdf,%al # Enable 124 outb %al,$0x60 # A20 125 sti # Enable interrupts 126 ret # To caller 127 128# Local read from disk 129 130nread: movwir(MEM_BUF,_bx) # Transfer buffer 131 movw1r(0x8,_si_,_ax) # Get 132 movw1r(0xa,_si_,_cx) # LBA 133 pushl %cs # Read from 134 callwi(xread.1) # disk 135 jnc return # If success 136 movwir(msg_read,_si) # Message 137 138# Error exit 139 140error: callwi(putstr) # Display message 141 movwir(prompt,_si) # Display 142 callwi(putstr) # prompt 143 xorb %ah,%ah # BIOS: Get 144 int $0x16 # keypress 145 int $0x19 # BIOS: Reboot 146 147# Display string 148 149putstr.0: movwir(0x7,_bx) # Page:attribute 150 movb $0xe,%ah # BIOS: Display 151 int $0x10 # character 152putstr: lodsb # Get char 153 testb %al,%al # End of string? 154 jne putstr.0 # No 155 156ereturn: movb $0x1,%ah # Invalid 157 stc # argument 158return: ret # To caller 159 160# Read from disk 161 162read: cs_ # LBA support 163 tstbim(0x80,MEM_REL+flags-start)# enabled? 164 jz read.1 # No 165 movwir(0x55aa,_bx) # Magic 166 pushl %edx # Save 167 movb $0x41,%ah # BIOS: Check 168 int $0x13 # extensions present 169 popl %edx # Restore 170 jc read.1 # If error 171 cmpwir(0xaa55,_bx) # Magic? 172 jne read.1 # No 173 testb $0x1,%cl # Packet interface? 174 jz read.1 # No 175 movl %ebp,%esi # Disk packet 176 movb $0x42,%ah # BIOS: Extended 177 int $0x13 # read 178 ret # To caller 179 180read.1: pushl %edx # Save 181 movb $0x8,%ah # BIOS: Get drive 182 int $0x13 # parameters 183 movb %dh,%ch # Max head number 184 popl %edx # Restore 185 jc return # If error 186 andb $0x3f,%cl # Sectors per track 187 jz ereturn # If zero 188 cli # Disable interrupts 189 o16 # Get 190 movw1r(0x8,_bp_,_ax) # LBA 191 pushl %edx # Save 192 movzbw %cl,%bx # Divide by 193 xorw %dx,%dx # sectors 194 divw %bx,%ax # per track 195 movb %ch,%bl # Max head number 196 movb %dl,%ch # Sector number 197 incl %ebx # Divide by 198 xorb %dl,%dl # number 199 divw %bx,%ax # of heads 200 movb %dl,%bh # Head number 201 popl %edx # Restore 202 o16 # Cylinder number 203 cmpl $0x3ff,%eax # supportable? 204 sti # Enable interrupts 205 ja ereturn # No 206 xchgb %al,%ah # Set up cylinder 207 rorb $0x2,%al # number 208 orb %ch,%al # Merge 209 incl %eax # sector 210 xchgl %eax,%ecx # number 211 movb %bh,%dh # Head number 212 subb %ah,%al # Sectors this track 213 movb1r(0x2,_bp_,_ah) # Blocks to read 214 cmpb %ah,%al # To read 215 jb read.2 # this 216 movb %ah,%al # track 217read.2: movwir(0x5,_di) # Try count 218read.3: lesw1r(0x4,_bp_,_bx) # Transfer buffer 219 pushl %eax # Save 220 movb $0x2,%ah # BIOS: Read 221 int $0x13 # from disk 222 popl %ebx # Restore 223 jnc read.4 # If success 224 decl %edi # Retry? 225 jz read.6 # No 226 xorb %ah,%ah # BIOS: Reset 227 int $0x13 # disk system 228 xchgl %ebx,%eax # Block count 229 jmp read.3 # Continue 230read.4: movzbl %bl,%eax # Sectors read 231 addwr1(_ax,0x8,_bp_) # Adjust 232 jnc read.5 # LBA, 233 incw1(0xa,_bp_) # transfer 234read.5: shlb %bl # buffer 235 addbr1(_bl,0x5,_bp_) # pointer, 236 subbr1(_al,0x2,_bp_) # block count 237 ja read.1 # If not done 238read.6: ret # To caller 239 240# Messages 241 242msg_read: .asciz "Read" 243msg_part: .asciz "Boot" 244 245prompt: .asciz " error\r\n" 246 247flags: .byte FLAGS # Flags 248 249 .org PRT_OFF,0x90 250 251# Partition table 252 253 .fill 0x30,0x1,0x0 254part4: .byte 0x80, 0x00, 0x01, 0x00 255 .byte 0xa5, 0xff, 0xff, 0xff 256 .byte 0x00, 0x00, 0x00, 0x00 257 .byte 0x50, 0xc3, 0x00, 0x00 258 259 .word 0xaa55 # Magic number 260