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1.1 ! root 1: /* ! 2: * Ported to boot 386BSD by Julian Elischer, September 1992 ! 3: * ! 4: * Mach Operating System ! 5: * Copyright (c) 1992, 1991 Carnegie Mellon University ! 6: * All Rights Reserved. ! 7: * ! 8: * Permission to use, copy, modify and distribute this software and its ! 9: * documentation is hereby granted, provided that both the copyright ! 10: * notice and this permission notice appear in all copies of the ! 11: * software, derivative works or modified versions, and any portions ! 12: * thereof, and that both notices appear in supporting documentation. ! 13: * ! 14: * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" ! 15: * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR ! 16: * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. ! 17: * ! 18: * Carnegie Mellon requests users of this software to return to ! 19: * ! 20: * Software Distribution Coordinator or [email protected] ! 21: * School of Computer Science ! 22: * Carnegie Mellon University ! 23: * Pittsburgh PA 15213-3890 ! 24: * ! 25: * any improvements or extensions that they make and grant Carnegie Mellon ! 26: * the rights to redistribute these changes. ! 27: */ ! 28: ! 29: /* ! 30: * HISTORY ! 31: * $Log: README.MACH,v $ ! 32: * Revision 1.1 1993/03/21 18:08:16 cgd ! 33: * after 0.2.2 "stable" patches applied ! 34: * ! 35: * Revision 2.2 92/04/04 11:33:55 rpd ! 36: * From 2.5 ! 37: * [92/03/30 mg32] ! 38: * ! 39: */ ! 40: ! 41: ********NOTE: This is not all relevant to the 386BSD version********** ! 42: ! 43: AT386 Protected Mode Bootstrap Loader ! 44: ===================================== ! 45: ! 46: 1. Overview of Startup ! 47: ------------------- ! 48: ! 49: After the system is rebooted, the BIOS bootstrap routine reads Sector ! 50: 1, Track 0 into memory at location 0000:7C00H. If location 0000:7DFEH ! 51: (last two bytes of that sector) contains the value AA55H, the BIOS ! 52: bootstrap routine will transfer control to 0000:7C00H. Otherwise, the ! 53: boot code in that sector is bad and the boot routine stops. ! 54: ! 55: For DOS compatibility reason, one extra stage of boot is required if ! 56: the boot device is a hard disk. The first sector of the hard disk will ! 57: contain the MOS-DOS boot code and a boot record partition table. ! 58: When this sector is loaded into 0000:7C00H, it will relocate itself ! 59: to somewhere else and then load the first sector of the active ! 60: partition into 0000:7C00H. Both UNIX and DOS use the command "fdisk" ! 61: [ 386bsd does not have an 'fdisk' (yet) ] ! 62: to install this first sector into the hard disk and to manipulate ! 63: the hard disk partitions. ! 64: ! 65: ! 66: ! 67: 2. The First Stage Bootstrap Loader ! 68: -------------------------------- ! 69: ! 70: After startup, the first stage boot is loaded at 0000:7C00H. This ! 71: first stage boot will load itself and the second stage boot into ! 72: memory at location 0000:1000H. For floppy disks, the first cylinder ! 73: is reserved as the boot cylinder, and the boot code (first and second) ! 74: will be loaded from there. Currently, only double sided, high density ! 75: (15 sectors per track) floppies are supported. For hard disks, the ! 76: first 29 sectors of the active partition is reserved for boot code ! 77: which will be loaded by the first stage boot. All the disk types ! 78: recognized by BIOS are supported by this bootstrap loader. ! 79: [for 386bsd we load the second stage booter to 9000:0] ! 80: ! 81: ! 82: ! 83: 3. The Second Stage Bootstrap Loader ! 84: -------------------------------- ! 85: ! 86: After the boot code is loaded, the control is passed to the second ! 87: stage bootstrap loader "boot2()". In order to be able to load the ! 88: big kernel image (bigger than 512K or 640K, depends on the memory ! 89: configuration), the second stage boot loader will run on the protected ! 90: mode. This bootstarp loader does not have any stand alone device ! 91: drivers, all the I/O's are through the BIOS calls. Since the first ! 92: stage boot code will no longer be used at this moment, the memory ! 93: location of the first stage boot code (0000:1000H to 0000:1200H) will ! 94: be used as an internal buffer for BIOS calls. Immediately after this ! 95: internal buffer is the GDT table for the second stage boot loader. ! 96: Since this boot loader needs to switch back and forth between protected ! 97: and real mode in order to use BIOS calls, the limit of the boot code ! 98: and boot data segments must not be greater than 64K. ! 99: ! 100: The boot loader loads the kernel image at memory location above 1 MB ! 101: to skip the memory hole between 521K/640K and 1MB. After the kernel ! 102: is loaded, the boot loader stores the information in the stack and ! 103: then passes control to kernel. Currently, the three information passed ! 104: fromm the boot loader to the kernel are type of the boot device, size ! 105: of the base memory and size of the extended memory. ! 106: ! 107: [ 386bsd receives: howto, bootdev] ! 108: ! 109: [ 386bsd is loaded where-ever the "MByte" bits of the load address specify, ! 110: so if you link it for FE100000 it will load to 1MB, but if you link ! 111: it for FE000000 it will load ad 0MB] ! 112: ! 113: [for machines with only 512KB normal ram the kernel will need to be linked ! 114: for 1MB and the bootblocks modified to run below 512KB. (8000:0)] ! 115: ! 116: ! 117: 4. The UNIX Startup ! 118: ---------------- ! 119: ! 120: Since the boot loader loads the kernel image at memory location above ! 121: 1MB, the kernel has to start as protected mode. In addition, the ! 122: link editor description file (vuifile) has to indicate that ! 123: the text and data segments start above 1MB. Also, the boot loader ! 124: passes the infomation to the kernel through the stack. ! 125: ! 126: [MOST of what is mentionned below is NOT relevant to 386bsd] ! 127: ! 128: 5. Disk Layout and Bad Block Handling ! 129: --------------------------------- ! 130: ! 131: The System V/386 Release 3.2 (AT) disk layout will be used as the disk ! 132: layout for the MACH System on the AT platform. ! 133: ! 134: This disk layout is as follows: ! 135: ! 136: * Reserve the first sector of cylinder 0 for the DOS boot record which ! 137: contains the master boot code (446 bytes) and the partition table. ! 138: (Refer to DOS Technical Reference Manual page 9-6 to 9-10). ! 139: ! 140: * Reserve the first 29 sectors of the UNIX partition for the first ! 141: and the second stage bootstrap. ! 142: ! 143: * Reserve the 30th sector of the UNIX partition for the pdinfo and ! 144: the vtoc tables. ! 145: ! 146: * Reserve the 31st to the 34th sectors of the UNIX partition for the ! 147: bad track and the bad block mapping tables. ! 148: ! 149: * Reserve up to 253 consecutive tracks when required, beginning with ! 150: the 35th sector of the UNIX partition, for alternate tracks. ! 151: ! 152: * Reserve up to 253 consecutive blocks, beginning with the first ! 153: sector after the alternate tracks area, for alternate blocks. ! 154: ! 155: SEC ! 156: 1 ! 157: ---------------------------------------------------- ! 158: | X | | CYL 0, TRK 0 ! 159: ---------------- .......... -------------------- ! 160: | .......... | ! 161: ---------------- .......... -------------------- ! 162: | .......... | ! 163: =============================================================== ! 164: ^ | BOOTSTRAP | CYL N, TRK M ! 165: | ---------------------------------------------------- ! 166: | | |30 |31 |32 |33 |34 | ! 167: ---------------------------------------------------- --- ! 168: U | .......... | ^ ! 169: N ---------------- .......... --------------------- | ! 170: I | .......... | Alternate Tracks ! 171: X ---------------- .......... --------------------- | ! 172: | .......... | V ! 173: P ---------------------------------------------------- --- ! 174: A | .......... | ^ ! 175: R ---------------- .......... --------------------- | ! 176: T | .......... | Alternate Blocks ! 177: I ---------------- .......... -------------------- | ! 178: T | .......... | V ! 179: I ---------------------------------------------------- --- ! 180: O | Unix root partition starts from here | ! 181: N ---------------- ----------------- ! 182: | | ! 183: ---------------------------------------------------- ! 184: | | ! 185: ---------------------------------------------------- ! 186: | | ! 187: | --------------------------------------------------- ! 188: | | | ! 189: | ---------------------------------------------------- ! 190: V | | ! 191: =============================================================== ! 192: | ........ | ! 193: --------------- ........ -------------- ! 194: | ........ | ! 195: ---------------------------------------------------- ! 196: ! 197: ! 198: The bad block handling mechanism is as follows: ! 199: ! 200: * Use the alternate track in the alternate tracks area if the ! 201: track containing the target sector is bad. ! 202: ! 203: * Use the alternate block in the alternate blocks area if the ! 204: target sector is bad. ! 205: ! 206: ! 207: ! 208: ! 209: 6. How to make: ! 210: ----------- ! 211: ! 212: Since the kernel image is loaded above 1 MB, the kernel must start ! 213: as protected mode. This means that this bootstrap loader will work ! 214: only when the corresponding changes on the kernel startup code are done. ! 215: ! 216: The make command to generate this bootstrap loader is: ! 217: ! 218: make -f boot.mk fdboot (floppy boot loader) ! 219: make -f boot.mk hdboot (wini boot loader) ! 220: [to make 386bsd bootblocks "make sd wd" (warning: they will be installed ! 221: in /dev/mdec.. take backups)]
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