cdboot.S revision 1.2
1 /* $NetBSD: cdboot.S,v 1.2 2005/07/06 09:22:31 junyoung Exp $ */ 2 3 /*- 4 * Copyright (c) 2005 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Bang Jun-Young. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 /* 40 * This is a primary boot loader that loads a secondary boot loader 41 * directly from CD without performing floppy/hard disk emulation as 42 * described by the El Torito specification. 43 * 44 * TODO: 45 * - Support for loading secondary boot loader > 64kB 46 */ 47 48 #include <machine/asm.h> 49 50 #define BOOT_ADDR 0x7c00 51 #define BLOCK_SIZE 2048 /* Default for ISO 9660 */ 52 #define VD_LBA 16 /* LBA of Volume Descriptor (VD) */ 53 #define PVD_ADDR 0x1000 /* Where Primary VD is loaded */ 54 #define ROOTDIR_ADDR 0x1800 /* Where Root Directory is loaded */ 55 #define LOADER_ADDR SECONDARY_LOAD_ADDRESS 56 57 /* 58 * Disk error codes 59 */ 60 #define ERROR_TIMEOUT 0x80 61 62 /* 63 * Volume Descriptor types. 64 */ 65 #define VD_PRIMARY 1 66 #define VD_SUPPLEMENTARY 2 67 #define VD_TERMINATOR 255 68 69 /* Only actually used entries are listed below */ 70 71 /* 72 * Format of Primary Volume Descriptor (8.4) 73 */ 74 #define PVD_ROOT_DR 156 /* Offset of Root Directory Record */ 75 76 /* 77 * Format of Directory Record (9.1) 78 */ 79 #define DR_LEN 0 80 #define DR_EXTENT 2 81 #define DR_DATA_LEN 10 82 #define DR_NAME_LEN 32 83 #define DR_NAME 33 84 85 .text 86 .code16 87 ENTRY(start) 88 xorw %ax, %ax 89 movw %ax, %ds 90 movw %ax, %es 91 movw %ax, %ss 92 movw $BOOT_ADDR, %sp 93 movw %sp, %si 94 movw $start, %di 95 movw $BLOCK_SIZE/2, %cx 96 rep 97 movsw 98 ljmp $0, $real_start 99 100 real_start: 101 movb %dl, boot_drive /* Save boot drive number */ 102 103 movw $0x475, %si /* Check presence of hard disks */ 104 movb (%si), %al 105 testb %al, %al 106 jz boot_cdrom 107 108 movw $str_press_key, %si 109 call message 110 next_second: 111 movw $str_dot, %si 112 call message 113 decb wait_count 114 jz boot_hard_disk 115 xorb %ah, %ah /* Get system time */ 116 int $0x1a 117 movw %dx, %di /* %cx:%dx = number of clock ticks */ 118 addw $19, %di /* 19 ~= 18.2 Hz */ 119 wait_key: 120 movb $1, %ah /* Check for keystroke */ 121 int $0x16 122 jz not_avail /* ZF clear if keystroke available */ 123 xorb %ah, %ah /* Read key to flush keyboard buf */ 124 int $0x16 125 jmp boot_cdrom 126 not_avail: 127 xorb %ah, %ah /* Get system time */ 128 int $0x1a 129 cmpw %dx, %di /* Compare with saved time */ 130 jnz wait_key 131 jmp next_second 132 133 boot_hard_disk: 134 movw $str_crlf, %si 135 call message 136 movw $0x0201, %ax /* %al = number of sectors to read */ 137 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 138 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 139 /* %cl = high 2 bits of cyl no & */ 140 /* sector number */ 141 movw $0x0080, %dx /* %dh = head number */ 142 /* %dl = disk number */ 143 int $0x13 /* Read MBR into memory */ 144 jc panic /* CF set on error */ 145 movw %cs, %ax /* Restore initial state */ 146 movw %ax, %ds 147 movw %ax, %es 148 movw $0x0080, %dx /* %dl = boot drive number */ 149 jmp $0, $BOOT_ADDR /* Jump to MBR! */ 150 151 panic: 152 hlt 153 jmp panic 154 155 boot_cdrom: 156 movw $str_banner, %si 157 call message 158 movl $VD_LBA, %eax 159 next_block: 160 movb $1, %dh /* Number of sectors to read */ 161 movl $PVD_ADDR, %ebx 162 call read_sectors 163 cmpb $VD_PRIMARY, (%bx) /* Is it Primary Volume Descriptor? */ 164 jz pvd_found 165 incl %eax 166 cmpb $VD_TERMINATOR, (%bx) 167 jnz next_block 168 movw $str_no_pvd, %si 169 call message 170 jmp panic 171 172 pvd_found: 173 movw $PVD_ADDR+PVD_ROOT_DR, %bx 174 movl DR_EXTENT(%bx), %eax /* LBA of the root directory */ 175 movl DR_DATA_LEN(%bx), %edx 176 shrl $11, %edx /* Convert to number of sectors */ 177 movb %dl, %dh /* ... and load it to %dh */ 178 movl $ROOTDIR_ADDR, %ebx 179 call read_sectors 180 next_entry: 181 cmpb $0, DR_LEN(%bx) 182 jz last_entry 183 movw %bx, %si 184 addw $DR_NAME, %si 185 movb DR_NAME_LEN(%bx), %cl 186 movw $str_loader, %di 187 1: 188 movb (%si), %al 189 cmpb %al, (%di) 190 jnz fail 191 incw %si 192 incw %di 193 decb %cl 194 jnz 1b 195 jmp load_loader 196 fail: 197 addw DR_LEN(%bx), %bx 198 jmp next_entry 199 last_entry: 200 movw $str_no_loader, %si 201 call message 202 jmp panic 203 204 load_loader: 205 movl DR_EXTENT(%bx), %eax 206 movl DR_DATA_LEN(%bx), %edx 207 addl $(BLOCK_SIZE-1), %edx /* Convert file length to */ 208 shrl $11, %edx /* ... number of sectors */ 209 movb %dl, %dh 210 movl $LOADER_ADDR, %ebx 211 call read_sectors 212 xorl %esi, %esi /* Don't provide boot_params */ 213 xorl %edx, %edx 214 movb boot_drive, %dl 215 xorl %ebx, %ebx /* Zero sector number */ 216 lcall $LOADER_ADDR/16, $0 217 jmp panic 218 219 /* 220 * Read disk sector(s) into memory 221 * 222 * %eax = LBA of starting sector 223 * %ebx = buffer to store sectors 224 * %dh = number of sectors to read 225 */ 226 read_sectors: 227 pusha 228 movl %eax, edd_lba /* Convert LBA to segment */ 229 shrl $4, %ebx 230 movw %bx, edd_segment 231 movb %dh, edd_nsecs 232 movb boot_drive, %dl 233 movw $edd_packet, %si 234 read_again: 235 movb $0x42, %ah 236 int $0x13 237 jc read_fail 238 popa 239 ret 240 read_fail: 241 cmpb $ERROR_TIMEOUT, %ah 242 jz read_again 243 movw $str_read_error, %si 244 call message 245 jmp panic 246 247 /* 248 * For debugging purpose 249 */ 250 put_char: 251 pusha 252 movb $0x0e, %ah 253 movw $0x0001, %bx 254 int $0x10 255 popa 256 ret 257 258 #include <message.S> 259 260 edd_packet: 261 edd_len: .word 16 262 edd_nsecs: .word 0 /* Number of sectors to transfer */ 263 edd_offset: .word 0 264 edd_segment: .word 0 265 edd_lba: .quad 0 266 267 wait_count: .byte 6 268 boot_drive: .byte 0 269 270 str_banner: .ascii "\r\nNetBSD/i386 cd9660 Primary Bootstrap" 271 str_crlf: .asciz "\r\n" 272 str_press_key: .asciz "\r\nPress any key to boot from CD" 273 str_dot: .asciz "." 274 str_read_error: .asciz "Can't read CD" 275 str_no_pvd: .asciz "Can't find Primary Volume Descriptor" 276 str_no_loader: .asciz "Can't find /boot" 277 str_loader: .asciz "BOOT.;1" 278 279 /* Used to calculate free bytes */ 280 free_space = end - . 281 282 . = start + BLOCK_SIZE 283 end: 284
Indexes created Thu Oct 02 07:10:07 GMT 2025