Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/i386at/boot/
Version:
- FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
SearchContext: - none - 3 - 10
SearchContext: - none - 3 - 10
| Name | Size | Last modified (GMT) | Description | |
| Parent directory | 2008-12-15 18:00:04 | ||
| Makeconf | 0 bytes | 1992-04-09 18:48:10 | |
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| Makefile | 2133 bytes | 1993-09-01 21:14:32 | |
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| Makefile.bnr | 2238 bytes | 1993-06-02 16:38:13 | |
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| README | 8664 bytes | 1992-04-09 18:48:12 | |
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| asm.s | 4843 bytes | 1993-06-02 15:10:27 | |
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| bios.s | 6640 bytes | 1993-06-02 15:10:32 | |
| boot.c | 6455 bytes | 1993-09-01 21:14:33 | |
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| boot.h | 1974 bytes | 1993-09-01 21:14:34 | |
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| boot.sed | 39 bytes | 1992-04-09 18:48:16 | |
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| boot2.s | 1472 bytes | 1992-04-09 18:48:17 | |
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| disk.c | 6806 bytes | 1993-09-01 21:14:34 | |
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| io.c | 3961 bytes | 1992-04-09 18:48:19 | |
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| rmaouthdr | 179 bytes | 1992-04-09 18:48:21 | |
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| start.s | 5604 bytes | 1993-09-01 21:14:35 | |
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| sys.c | 4866 bytes | 1993-09-01 21:14:35 | |
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| table.c | 4054 bytes | 1993-06-02 15:10:37 |
1 /* 2 * Mach Operating System 3 * Copyright (c) 1992, 1991 Carnegie Mellon University 4 * All Rights Reserved. 5 * 6 * Permission to use, copy, modify and distribute this software and its 7 * documentation is hereby granted, provided that both the copyright 8 * notice and this permission notice appear in all copies of the 9 * software, derivative works or modified versions, and any portions 10 * thereof, and that both notices appear in supporting documentation. 11 * 12 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 13 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 14 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 15 * 16 * Carnegie Mellon requests users of this software to return to 17 * 18 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 19 * School of Computer Science 20 * Carnegie Mellon University 21 * Pittsburgh PA 15213-3890 22 * 23 * any improvements or extensions that they make and grant Carnegie Mellon 24 * the rights to redistribute these changes. 25 */ 26 27 /* 28 * HISTORY 29 * $Log: README,v $ 30 * Revision 2.2 92/04/04 11:33:55 rpd 31 * From 2.5 32 * [92/03/30 mg32] 33 * 34 */ 35 36 AT386 Protected Mode Bootstrap Loader 37 ===================================== 38 39 1. Overview of Startup 40 ------------------- 41 42 After the system is rebooted, the BIOS bootstrap routine reads Sector 43 1, Track 0 into memory at location 0000:7C00H. If location 0000:7DFEH 44 (last two bytes of that sector) contains the value AA55H, the BIOS 45 bootstrap routine will transfer control to 0000:7C00H. Otherwise, the 46 boot code in that sector is bad and the boot routine stops. 47 48 For DOS compatibility reason, one extra stage of boot is required if 49 the boot device is a hard disk. The first sector of the hard disk will 50 contain the MOS-DOS boot code and a boot record partition table. 51 When this sector is loaded into 0000:7C00H, it will relocate itself 52 to somewhere else and then load the first sector of the active 53 partition into 0000:7C00H. Both UNIX and DOS use the command "fdisk" 54 to install this first sector into the hard disk and to manipulate 55 the hard disk partitions. 56 57 58 59 2. The First Stage Bootstrap Loader 60 -------------------------------- 61 62 After startup, the first stage boot is loaded at 0000:7C00H. This 63 first stage boot will load itself and the second stage boot into 64 memory at location 0000:1000H. For floppy disks, the first cylinder 65 is reserved as the boot cylinder, and the boot code (first and second) 66 will be loaded from there. Currently, only double sided, high density 67 (15 sectors per track) floppies are supported. For hard disks, the 68 first 29 sectors of the active partition is reserved for boot code 69 which will be loaded by the first stage boot. All the disk types 70 recognized by BIOS are supported by this bootstrap loader. 71 72 73 74 3. The Second Stage Bootstrap Loader 75 -------------------------------- 76 77 After the boot code is loaded, the control is passed to the second 78 stage bootstrap loader "boot2()". In order to be able to load the 79 big kernel image (bigger than 512K or 640K, depends on the memory 80 configuration), the second stage boot loader will run on the protected 81 mode. This bootstarp loader does not have any stand alone device 82 drivers, all the I/O's are through the BIOS calls. Since the first 83 stage boot code will no longer be used at this moment, the memory 84 location of the first stage boot code (0000:1000H to 0000:1200H) will 85 be used as an internal buffer for BIOS calls. Immediately after this 86 internal buffer is the GDT table for the second stage boot loader. 87 Since this boot loader needs to switch back and forth between protected 88 and real mode in order to use BIOS calls, the limit of the boot code 89 and boot data segments must not be greater than 64K. 90 91 The boot loader loads the kernel image at memory location above 1 MB 92 to skip the memory hole between 521K/640K and 1MB. After the kernel 93 is loaded, the boot loader stores the information in the stack and 94 then passes control to kernel. Currently, the three information passed 95 fromm the boot loader to the kernel are type of the boot device, size 96 of the base memory and size of the extended memory. 97 98 99 4. The UNIX Startup 100 ---------------- 101 102 Since the boot loader loads the kernel image at memory location above 103 1MB, the kernel has to start as protected mode. In addition, the 104 link editor description file (vuifile) has to indicate that 105 the text and data segments start above 1MB. Also, the boot loader 106 passes the infomation to the kernel through the stack. 107 108 109 5. Disk Layout and Bad Block Handling 110 --------------------------------- 111 112 The System V/386 Release 3.2 (AT) disk layout will be used as the disk 113 layout for the MACH System on the AT platform. 114 115 This disk layout is as follows: 116 117 * Reserve the first sector of cylinder 0 for the DOS boot record which 118 contains the master boot code (446 bytes) and the partition table. 119 (Refer to DOS Technical Reference Manual page 9-6 to 9-10). 120 121 * Reserve the first 29 sectors of the UNIX partition for the first 122 and the second stage bootstrap. 123 124 * Reserve the 30th sector of the UNIX partition for the pdinfo and 125 the vtoc tables. 126 127 * Reserve the 31st to the 34th sectors of the UNIX partition for the 128 bad track and the bad block mapping tables. 129 130 * Reserve up to 253 consecutive tracks when required, beginning with 131 the 35th sector of the UNIX partition, for alternate tracks. 132 133 * Reserve up to 253 consecutive blocks, beginning with the first 134 sector after the alternate tracks area, for alternate blocks. 135 136 SEC 137 1 138 ---------------------------------------------------- 139 | X | | CYL 0, TRK 0 140 ---------------- .......... -------------------- 141 | .......... | 142 ---------------- .......... -------------------- 143 | .......... | 144 =============================================================== 145 ^ | BOOTSTRAP | CYL N, TRK M 146 | ---------------------------------------------------- 147 | | |30 |31 |32 |33 |34 | 148 ---------------------------------------------------- --- 149 U | .......... | ^ 150 N ---------------- .......... --------------------- | 151 I | .......... | Alternate Tracks 152 X ---------------- .......... --------------------- | 153 | .......... | V 154 P ---------------------------------------------------- --- 155 A | .......... | ^ 156 R ---------------- .......... --------------------- | 157 T | .......... | Alternate Blocks 158 I ---------------- .......... -------------------- | 159 T | .......... | V 160 I ---------------------------------------------------- --- 161 O | Unix root partition starts from here | 162 N ---------------- ----------------- 163 | | 164 ---------------------------------------------------- 165 | | 166 ---------------------------------------------------- 167 | | 168 | --------------------------------------------------- 169 | | | 170 | ---------------------------------------------------- 171 V | | 172 =============================================================== 173 | ........ | 174 --------------- ........ -------------- 175 | ........ | 176 ---------------------------------------------------- 177 178 179 The bad block handling mechanism is as follows: 180 181 * Use the alternate track in the alternate tracks area if the 182 track containing the target sector is bad. 183 184 * Use the alternate block in the alternate blocks area if the 185 target sector is bad. 186 187 188 189 190 6. How to make: 191 ----------- 192 193 Since the kernel image is loaded above 1 MB, the kernel must start 194 as protected mode. This means that this bootstrap loader will work 195 only when the corresponding changes on the kernel startup code are done. 196 197 The make command to generate this bootstrap loader is: 198 199 make -f boot.mk fdboot (floppy boot loader) 200 make -f boot.mk hdboot (wini boot loader)
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