cdboot.S revision 1.1
1 /* $NetBSD: cdboot.S,v 1.1 2005/06/15 06:38:45 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 movw $str_press_key, %si 103 call message 104 next_second: 105 movw $str_dot, %si 106 call message 107 decb wait_count 108 jz boot_hard_disk 109 xorb %ah, %ah /* Get system time */ 110 int $0x1a 111 movw %dx, %di /* %cx:%dx = number of clock ticks */ 112 addw $19, %di /* 19 ~= 18.2 Hz */ 113 wait_key: 114 movb $1, %ah /* Check for keystroke */ 115 int $0x16 116 jz not_avail /* ZF clear if keystroke available */ 117 xorb %ah, %ah /* Read key to flush keyboard buf */ 118 int $0x16 119 jmp boot_cdrom 120 not_avail: 121 xorb %ah, %ah /* Get system time */ 122 int $0x1a 123 cmpw %dx, %di /* Compare with saved time */ 124 jnz wait_key 125 jmp next_second 126 127 boot_hard_disk: 128 movw $str_crlf, %si 129 call message 130 movw $0x0201, %ax /* %al = number of sectors to read */ 131 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 132 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 133 /* %cl = high 2 bits of cyl no & */ 134 /* sector number */ 135 movw $0x0080, %dx /* %dh = head number */ 136 /* %dl = disk number */ 137 int $0x13 /* Read MBR into memory */ 138 jc panic /* CF set on error */ 139 movw %cs, %ax /* Restore initial state */ 140 movw %ax, %ds 141 movw %ax, %es 142 movw $0x0080, %dx /* %dl = boot drive number */ 143 jmp $0, $BOOT_ADDR /* Jump to MBR! */ 144 145 panic: 146 hlt 147 jmp panic 148 149 boot_cdrom: 150 movw $str_banner, %si 151 call message 152 movl $VD_LBA, %eax 153 next_block: 154 movb $1, %dh /* Number of sectors to read */ 155 movl $PVD_ADDR, %ebx 156 call read_sectors 157 cmpb $VD_PRIMARY, (%bx) /* Is it Primary Volume Descriptor? */ 158 jz pvd_found 159 incl %eax 160 cmpb $VD_TERMINATOR, (%bx) 161 jnz next_block 162 movw $str_no_pvd, %si 163 call message 164 jmp panic 165 166 pvd_found: 167 movw $PVD_ADDR+PVD_ROOT_DR, %bx 168 movl DR_EXTENT(%bx), %eax /* LBA of the root directory */ 169 movl DR_DATA_LEN(%bx), %edx 170 shrl $11, %edx /* Convert to number of sectors */ 171 movb %dl, %dh /* ... and load it to %dh */ 172 movl $ROOTDIR_ADDR, %ebx 173 call read_sectors 174 next_entry: 175 cmpb $0, DR_LEN(%bx) 176 jz last_entry 177 movw %bx, %si 178 addw $DR_NAME, %si 179 movb DR_NAME_LEN(%bx), %cl 180 movw $str_loader, %di 181 1: 182 movb (%si), %al 183 cmpb %al, (%di) 184 jnz fail 185 incw %si 186 incw %di 187 decb %cl 188 jnz 1b 189 jmp load_loader 190 fail: 191 addw DR_LEN(%bx), %bx 192 jmp next_entry 193 last_entry: 194 movw $str_no_loader, %si 195 call message 196 jmp panic 197 198 load_loader: 199 movl DR_EXTENT(%bx), %eax 200 movl DR_DATA_LEN(%bx), %edx 201 addl $(BLOCK_SIZE-1), %edx /* Convert file length to */ 202 shrl $11, %edx /* ... number of sectors */ 203 movb %dl, %dh 204 movl $LOADER_ADDR, %ebx 205 call read_sectors 206 xorl %esi, %esi /* Don't provide boot_params */ 207 xorl %edx, %edx 208 movb boot_drive, %dl 209 xorl %ebx, %ebx /* Zero sector number */ 210 lcall $LOADER_ADDR/16, $0 211 jmp panic 212 213 /* 214 * Read disk sector(s) into memory 215 * 216 * %eax = LBA of starting sector 217 * %ebx = buffer to store sectors 218 * %dh = number of sectors to read 219 */ 220 read_sectors: 221 pusha 222 movl %eax, edd_lba /* Convert LBA to segment */ 223 shrl $4, %ebx 224 movw %bx, edd_segment 225 movb %dh, edd_nsecs 226 movb boot_drive, %dl 227 movw $edd_packet, %si 228 read_again: 229 movb $0x42, %ah 230 int $0x13 231 jc read_fail 232 popa 233 ret 234 read_fail: 235 cmpb $ERROR_TIMEOUT, %ah 236 jz read_again 237 movw $str_read_error, %si 238 call message 239 jmp panic 240 241 /* 242 * For debugging purpose 243 */ 244 put_char: 245 pusha 246 movb $0x0e, %ah 247 movw $0x0001, %bx 248 int $0x10 249 popa 250 ret 251 252 #include <message.S> 253 254 edd_packet: 255 edd_len: .word 16 256 edd_nsecs: .word 0 /* Number of sectors to transfer */ 257 edd_offset: .word 0 258 edd_segment: .word 0 259 edd_lba: .quad 0 260 261 wait_count: .byte 6 262 boot_drive: .byte 0 263 264 str_banner: .ascii "\r\nNetBSD/i386 cd9660 Primary Bootstrap" 265 str_crlf: .asciz "\r\n" 266 str_press_key: .asciz "\r\nPress any key to boot from CD" 267 str_dot: .asciz "." 268 str_read_error: .asciz "Can't read CD" 269 str_no_pvd: .asciz "Can't find Primary Volume Descriptor" 270 str_no_loader: .asciz "Can't find /boot" 271 str_loader: .asciz "BOOT.;1" 272 273 /* Used to calculate free bytes */ 274 free_space = end - . 275 276 . = start + BLOCK_SIZE 277 end: 278
Indexes created Thu Oct 02 14:10:14 GMT 2025