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Diffstat (limited to 'sys/i386/boot/README.MACH')
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diff --git a/sys/i386/boot/README.MACH b/sys/i386/boot/README.MACH new file mode 100644 index 000000000000..d11f3e420372 --- /dev/null +++ b/sys/i386/boot/README.MACH @@ -0,0 +1,218 @@ +/* + * Ported to boot 386BSD by Julian Elischer, September 1992 + * + * Mach Operating System + * Copyright (c) 1992, 1991 Carnegie Mellon University + * All Rights Reserved. + * + * Permission to use, copy, modify and distribute this software and its + * documentation is hereby granted, provided that both the copyright + * notice and this permission notice appear in all copies of the + * software, derivative works or modified versions, and any portions + * thereof, and that both notices appear in supporting documentation. + * + * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" + * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR + * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. + * + * Carnegie Mellon requests users of this software to return to + * + * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU + * School of Computer Science + * Carnegie Mellon University + * Pittsburgh PA 15213-3890 + * + * any improvements or extensions that they make and grant Carnegie Mellon + * the rights to redistribute these changes. + */ + +/* + * HISTORY + * $Log: README,v $ + * Revision 2.2 92/04/04 11:33:55 rpd + * From 2.5 + * [92/03/30 mg32] + * + */ + +********NOTE: This is not all relevant to the 386BSD version********** + + AT386 Protected Mode Bootstrap Loader + ===================================== + +1. Overview of Startup + ------------------- + + After the system is rebooted, the BIOS bootstrap routine reads Sector + 1, Track 0 into memory at location 0000:7C00H. If location 0000:7DFEH + (last two bytes of that sector) contains the value AA55H, the BIOS + bootstrap routine will transfer control to 0000:7C00H. Otherwise, the + boot code in that sector is bad and the boot routine stops. + + For DOS compatibility reason, one extra stage of boot is required if + the boot device is a hard disk. The first sector of the hard disk will + contain the MOS-DOS boot code and a boot record partition table. + When this sector is loaded into 0000:7C00H, it will relocate itself + to somewhere else and then load the first sector of the active + partition into 0000:7C00H. Both UNIX and DOS use the command "fdisk" +[ 386bsd does not have an 'fdisk' (yet) ] + to install this first sector into the hard disk and to manipulate + the hard disk partitions. + + + +2. The First Stage Bootstrap Loader + -------------------------------- + + After startup, the first stage boot is loaded at 0000:7C00H. This + first stage boot will load itself and the second stage boot into + memory at location 0000:1000H. For floppy disks, the first cylinder + is reserved as the boot cylinder, and the boot code (first and second) + will be loaded from there. Currently, only double sided, high density + (15 sectors per track) floppies are supported. For hard disks, the + first 29 sectors of the active partition is reserved for boot code + which will be loaded by the first stage boot. All the disk types + recognized by BIOS are supported by this bootstrap loader. +[for 386bsd we load the second stage booter to 9000:0] + + + +3. The Second Stage Bootstrap Loader + -------------------------------- + + After the boot code is loaded, the control is passed to the second + stage bootstrap loader "boot2()". In order to be able to load the + big kernel image (bigger than 512K or 640K, depends on the memory + configuration), the second stage boot loader will run on the protected + mode. This bootstarp loader does not have any stand alone device + drivers, all the I/O's are through the BIOS calls. Since the first + stage boot code will no longer be used at this moment, the memory + location of the first stage boot code (0000:1000H to 0000:1200H) will + be used as an internal buffer for BIOS calls. Immediately after this + internal buffer is the GDT table for the second stage boot loader. + Since this boot loader needs to switch back and forth between protected + and real mode in order to use BIOS calls, the limit of the boot code + and boot data segments must not be greater than 64K. + + The boot loader loads the kernel image at memory location above 1 MB + to skip the memory hole between 521K/640K and 1MB. After the kernel + is loaded, the boot loader stores the information in the stack and + then passes control to kernel. Currently, the three information passed + fromm the boot loader to the kernel are type of the boot device, size + of the base memory and size of the extended memory. + +[ 386bsd receives: howto, bootdev] + +[ 386bsd is loaded where-ever the "MByte" bits of the load address specify, +so if you link it for FE100000 it will load to 1MB, but if you link +it for FE000000 it will load ad 0MB] + +[for machines with only 512KB normal ram the kernel will need to be linked +for 1MB and the bootblocks modified to run below 512KB. (8000:0)] + + +4. The UNIX Startup + ---------------- + + Since the boot loader loads the kernel image at memory location above + 1MB, the kernel has to start as protected mode. In addition, the + link editor description file (vuifile) has to indicate that + the text and data segments start above 1MB. Also, the boot loader + passes the infomation to the kernel through the stack. + +[MOST of what is mentionned below is NOT relevant to 386bsd] + +5. Disk Layout and Bad Block Handling + --------------------------------- + + The System V/386 Release 3.2 (AT) disk layout will be used as the disk + layout for the MACH System on the AT platform. + + This disk layout is as follows: + + * Reserve the first sector of cylinder 0 for the DOS boot record which + contains the master boot code (446 bytes) and the partition table. + (Refer to DOS Technical Reference Manual page 9-6 to 9-10). + + * Reserve the first 29 sectors of the UNIX partition for the first + and the second stage bootstrap. + + * Reserve the 30th sector of the UNIX partition for the pdinfo and + the vtoc tables. + + * Reserve the 31st to the 34th sectors of the UNIX partition for the + bad track and the bad block mapping tables. + + * Reserve up to 253 consecutive tracks when required, beginning with + the 35th sector of the UNIX partition, for alternate tracks. + + * Reserve up to 253 consecutive blocks, beginning with the first + sector after the alternate tracks area, for alternate blocks. + + SEC + 1 + ---------------------------------------------------- + | X | | CYL 0, TRK 0 + ---------------- .......... -------------------- + | .......... | + ---------------- .......... -------------------- + | .......... | + =============================================================== + ^ | BOOTSTRAP | CYL N, TRK M + | ---------------------------------------------------- + | | |30 |31 |32 |33 |34 | + ---------------------------------------------------- --- + U | .......... | ^ + N ---------------- .......... --------------------- | + I | .......... | Alternate Tracks + X ---------------- .......... --------------------- | + | .......... | V + P ---------------------------------------------------- --- + A | .......... | ^ + R ---------------- .......... --------------------- | + T | .......... | Alternate Blocks + I ---------------- .......... -------------------- | + T | .......... | V + I ---------------------------------------------------- --- + O | Unix root partition starts from here | + N ---------------- ----------------- + | | + ---------------------------------------------------- + | | + ---------------------------------------------------- + | | + | --------------------------------------------------- + | | | + | ---------------------------------------------------- + V | | + =============================================================== + | ........ | + --------------- ........ -------------- + | ........ | + ---------------------------------------------------- + + + The bad block handling mechanism is as follows: + + * Use the alternate track in the alternate tracks area if the + track containing the target sector is bad. + + * Use the alternate block in the alternate blocks area if the + target sector is bad. + + + + +6. How to make: + ----------- + + Since the kernel image is loaded above 1 MB, the kernel must start + as protected mode. This means that this bootstrap loader will work + only when the corresponding changes on the kernel startup code are done. + + The make command to generate this bootstrap loader is: + + make -f boot.mk fdboot (floppy boot loader) + make -f boot.mk hdboot (wini boot loader) +[to make 386bsd bootblocks "make sd wd" (warning: they will be installed +in /dev/mdec.. take backups)] |