pc/ms DOS compatible boot sector
git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/branches/UNSTABLE@1028 6ac86273-5f31-0410-b378-82cca8765d1b
This commit is contained in:
Kenneth J Davis
parent
6e7415e7a4
commit
fce371ba94
598
boot/oemboot.asm
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598
boot/oemboot.asm
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;
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; File:
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; oemboot.asm
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; 2004, Kenneth J. Davis
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; Copyright (c) 200?, <add name here>
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; Description:
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; OEM boot sector for FreeDOS compatible with IBM's (R) PC-DOS,
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; and Microsoft's (R) PC-DOS. It may work with OpenDOS/DR-DOS,
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; although the standard FreeDOS boot sector works with later
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; releases. May work with other versions of DOS that use
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; IBMBIO.COM/IBMDOS.COM pair. This boot sector loads only up
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; to 58 sectors (29KB) of the kernel (IBMBIO.COM) to 0x70:0 then
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; jumps to it. As best I can tell, PC-DOS (and assuming MS-DOS
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; behaves similar) expects on entry for:
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; ch = media id byte in the boot sector
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; dl = BIOS drive booted from (0x00=A:, 0x80=C:, ...)
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; ax:bx = the LBA sector of 1st data sector 0x0000:0021 for FAT12
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; ?or? 1st sector of IBMBIO.COM (which is normally 1st data sector)
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; it also expects the boot sector (in particular the BPB)
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; to still be at 0x0:7C00, the directory entry for IBMBIO.COM
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; (generally first entry of first sector of the root directory)
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; at 0x50:0 (DOS Data Area). The original boot sector may update
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; the floppy disk parameter table (int 1Eh), but we don't so
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; may fail for any systems where the changes (???) are needed.
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; If the above conditions are not met, then IBMBIO.COM will
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; print the not a bootable disk error message.
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;
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; This boot sector only supports FAT12/FAT16 as PC-DOS
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; does not support FAT32 and newer FAT32 capable DOSes
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; probably have different boot requirements; also do NOT
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; use it to boot the FreeDOS kernel as it expects to be
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; fully loaded by boot sector (> 29KB & usually to 0x60:0).
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;
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; WARNING: PC-DOS has additional requirements, in particular,
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; it may expect that IBMBIO.COM and IBMDOS.COM be the 1st
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; two entries in the root directory (even before the label)
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; and that they occupy the 1st consecutive data sectors.
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; Newer releases may support other positions, but still
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; generally should occupy consecutive sectors. These conditions
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; can usually be met by running sys on a freshly formatted
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; and un-label'd disk.
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;
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;
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; Derived From:
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; boot.asm
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; DOS-C boot
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;
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; Copyright (c) 1997, 2000-2004
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; Svante Frey, Jim Hall, Jim Tabor, Bart Oldeman,
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; Tom Ehlert, Eric Auer, Luchezar Georgiev, Jon Gentle
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; and Michal H. Tyc (DR-DOS adaptation, boot26dr.asm)
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; All Rights Reserved
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;
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; This file is part of FreeDOS.
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;
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; DOS-C is free software; you can redistribute it and/or
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; modify it under the terms of the GNU General Public License
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; as published by the Free Software Foundation; either version
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; 2, or (at your option) any later version.
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;
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; DOS-C is distributed in the hope that it will be useful, but
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; WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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; the GNU General Public License for more details.
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;
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; You should have received a copy of the GNU General Public
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; License along with DOS-C; see the file COPYING. If not,
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; write to the Free Software Foundation, 675 Mass Ave,
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; Cambridge, MA 02139, USA.
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;
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;
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; +--------+
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; | CLUSTER|
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; | LIST |
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; |--------| 0000:7F00
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; |LBA PKT |
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; |--------| 0000:7E00 (0:BP+200)
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; |BOOT SEC| contains BPB
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; |ORIGIN |
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; |--------| 0000:7C00 (0:BP)
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; |STACK | minimal 256 bytes (1/2 sector)
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; |- - - - |
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; |KERNEL | kernel loaded here (max 58 sectors, 29KB)
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; |LOADED | also used as FAT buffer
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; |--------| 0070:0000 (0:0700)
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; |DOS DA/ | DOS Data Area,
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; |ROOT DIR| during boot the 1st sector of root directory
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; |--------| 0000:0500
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; |BDA | BIOS Data Area
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; +--------+ 0000:0400
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; |IVT | Interrupt Vector Table
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; +--------+ 0000:0000
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;%define ISFAT12 1 ; only 1 of these should be set,
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;%define ISFAT16 1 ; defines which FAT is supported
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%define TRYLBAREAD 1 ; undefine to use only CHS int 13h
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;%define LOOPONERR 1 ; if defined on error simply loop forever
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;%define SETROOTDIR 1 ; if defined dir entry copied to 0:500
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;%define RETRYALWAYS 1 ; if defined retries read forever
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;%define FORCEBIOSDRV 1 ; if defined always use boot drive from BIOS
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;%define MSCOMPAT 1 ; sets default filename to MSDOS IO.SYS
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segment .text
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%define BASE 0x7c00 ; boot sector originally at 0x0:BASE
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%define LOADSEG 0x0070 ; segment to load kernel at LOADSEG:0
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%define LOADEND 0x07b0 ; limit reads to below this segment
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; LOADSEG+29KB, else data overwritten
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%define FATBUF bp-0x7500 ; offset of temporary buffer for FAT
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; chain 0:FATBUF = 0:0700 = LOADSEG:0
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%define ROOTDIR bp-0x7700 ; offset to buffer for root directory
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; entry of kernel 0:ROOTDIR
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%define CLUSTLIST bp+0x0300 ; zero terminated list of clusters
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; that the kernel occupies
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; Some extra variables
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; using bp-Entry+variable_name generates smaller code than using just
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; variable_name, where bp is initialized to Entry, so bp-Entry equals 0
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%define LBA_PACKET bp+0x0200 ; immediately after boot sector
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%define LBA_SIZE word [LBA_PACKET] ; size of packet, should be 10h
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%define LBA_SECNUM word [LBA_PACKET+2] ; number of sectors to read
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%define LBA_OFF LBA_PACKET+4 ; buffer to read/write to
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%define LBA_SEG LBA_PACKET+6
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%define LBA_SECTOR_0 word [LBA_PACKET+8 ] ; LBA starting sector #
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%define LBA_SECTOR_16 word [LBA_PACKET+10]
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%define LBA_SECTOR_32 word [LBA_PACKET+12]
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%define LBA_SECTOR_48 word [LBA_PACKET+14]
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%define PARAMS LBA_PACKET+0x10
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;%define RootDirSecs PARAMS+0x0 ; # of sectors root dir uses
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%define fat_start PARAMS+0x2 ; first FAT sector
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;%define root_dir_start PARAMS+0x6 ; first root directory sector
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%define data_start PARAMS+0x0a ; first data sector
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;-----------------------------------------------------------------------
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org BASE
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Entry: jmp short real_start
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nop
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; bp is initialized to 7c00h
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%define bsOemName bp+0x03 ; OEM label
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%define bsBytesPerSec bp+0x0b ; bytes/sector
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%define bsSecPerClust bp+0x0d ; sectors/allocation unit
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%define bsResSectors bp+0x0e ; # reserved sectors
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%define bsFATs bp+0x10 ; # of fats
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%define bsRootDirEnts bp+0x11 ; # of root dir entries
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%define bsSectors bp+0x13 ; # sectors total in image
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%define bsMedia bp+0x15 ; media descrip: fd=2side9sec, etc...
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%define sectPerFat bp+0x16 ; # sectors in a fat
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%define sectPerTrack bp+0x18 ; # sectors/track
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%define nHeads bp+0x1a ; # heads
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%define nHidden bp+0x1c ; # hidden sectors
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%define nSectorHuge bp+0x20 ; # sectors if > 65536
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%define drive bp+0x24 ; drive number
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%define extBoot bp+0x26 ; extended boot signature
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%define volid bp+0x27
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%define vollabel bp+0x2b
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%define filesys bp+0x36
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;-----------------------------------------------------------------------
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; times 0x3E-$+$$ db 0
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;
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; Instead of zero-fill,
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; initialize BPB with values suitable for a 1440 K floppy
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;
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db 'IBM 5.0' ; OEM label
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dw 512 ; bytes per sector
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db 1 ; sectors per cluster
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dw 1 ; reserved sectors
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db 2 ; number of FATs
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dw 224 ; root directory entries
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dw 80 * 36 ; total sectors on disk
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db 0xF0 ; media descriptor
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dw 9 ; sectors per 1 FAT copy
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dw 18 ; sectors per track
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dw 2 ; number of heads
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dd 0 ; hidden sectors
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dd 0 ; big total sectors
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db 0 ; boot unit
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db 0 ; reserved
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db 0x29 ; extended boot record id
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dd 0x12345678 ; volume serial number
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db 'NO NAME '; volume label
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db 'FAT12 ' ; filesystem id
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;-----------------------------------------------------------------------
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; ENTRY
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;-----------------------------------------------------------------------
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real_start:
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cli ; disable interrupts until stack ready
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cld ; all string operations increment
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xor ax, ax ; ensure our segment registers ready
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mov ds, ax ; cs=ds=es=ss=0x0000
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mov es, ax
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mov ss, ax
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mov bp, BASE
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lea sp, [bp-2]
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; a reset should not be needed here
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; int 0x13 ; reset drive
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; For compatibility, diskette parameter vector updated.
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; lea di [bp+0x3E] ; just use bp for DR-DOS?
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; mov bx, 4 * 1eh ; stored at int 1E's vector
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; lds si, [bx] ; fetch current int 1eh pointer
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; mov cl, 11 ; the parameter table is 11 bytes
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; rep movsb ; and copy the parameter block
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; mov ds, ax ; restore DS
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sti ; enable interrupts
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;
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; Some BIOS don't pass drive number in DL, so don't use it if [drive] is known
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;
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%ifndef FORCEBIOSDRV
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cmp byte [drive], 0xff ; impossible number written by SYS
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jne dont_use_dl ; was SYS drive: other than A or B?
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%endif
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mov [drive], dl ; yes, rely on BIOS drive number in DL
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dont_use_dl: ; no, rely on [drive] written by SYS
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; GETDRIVEPARMS: Calculate start of some disk areas.
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;
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mov si, word [nHidden]
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mov di, word [nHidden+2]
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add si, word [bsResSectors]
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adc di, byte 0 ; DI:SI = first FAT sector
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mov word [fat_start], si
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mov word [fat_start+2], di
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mov al, [bsFATs]
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cbw
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mul word [sectPerFat] ; DX:AX = total number of FAT sectors
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add si, ax
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adc di, dx ; DI:SI = first root directory sector
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push di ; mov word [root_dir_start+2], di
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push si ; mov word [root_dir_start], si
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; Calculate how many sectors the root directory occupies.
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mov bx, [bsBytesPerSec]
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mov cl, 5 ; divide BX by 32
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shr bx, cl ; BX = directory entries per sector
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mov ax, [bsRootDirEnts]
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xor dx, dx
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div bx ; set AX = sectors per root directory
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push ax ; mov word [RootDirSecs], ax
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add si, ax
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adc di, byte 0 ; DI:SI = first data sector
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mov [data_start], si
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mov [data_start+2], di
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; FINDFILE: Searches for the file in the root directory.
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;
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; Returns:
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; AX = first cluster of file
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; First, read the root directory into buffer.
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; into the temporary buffer. (max 29KB or overruns stuff)
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pop di ; mov di, word [RootDirSecs]
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pop ax ; mov ax, word [root_dir_start]
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pop dx ; mov dx, word [root_dir_start+2]
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lea bx, [ROOTDIR] ; es:bx = 0:0500
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push es ; save pointer to ROOTDIR
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call readDisk
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pop es ; restore pointer to ROOTDIR
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lea si, [ROOTDIR] ; ds:si = 0:0500
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; Search for kernel file name, and find start cluster.
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next_entry: mov cx, 11
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mov di, filename
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push si
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repe cmpsb
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pop si
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mov ax, [si+0x1A]; get cluster number from directory entry
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je ffDone
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add si, byte 0x20 ; go to next directory entry
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jc near boot_error ; fail if not found and si wraps
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cmp byte [si], 0 ; if the first byte of the name is 0,
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jnz next_entry ; there are no more files in the directory
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ffDone:
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push ax ; store first cluster number
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%ifdef SETROOTDIR
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; copy over this portion of root dir to 0x0:500 for PC-DOS
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; (this may allow IBMBIO.COM to start in any directory entry)
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lea di, [ROOTDIR] ; es:di = 0:0500
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mov cx, 0x100
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rep movsw
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%endif
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; GETFATCHAIN:
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;
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; Reads the FAT chain and stores it in a temporary buffer in the first
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; 64 kb. The FAT chain is stored an array of 16-bit cluster numbers,
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; ending with 0.
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;
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; The file must fit in conventional memory, so it can't be larger than
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; 640 kb. The sector size must be at least 512 bytes, so the FAT chain
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; can't be larger than 2.5 KB (655360 / 512 * 2 = 2560).
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;
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; Call with: AX = first cluster in chain
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; Load the complete FAT into memory. The FAT can't be larger
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; than 128 kb
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lea bx, [FATBUF] ; es:bx = 0:0700
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mov di, [sectPerFat]
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mov ax, word [fat_start]
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mov dx, word [fat_start+2]
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call readDisk
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; Set ES:DI to the temporary storage for the FAT chain.
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push ds
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pop es
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lea di, [CLUSTLIST]
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; Set DS:0 to FAT data we loaded
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mov ax, LOADSEG
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mov ds, ax ; ds:0 = 0x70:0 = 0:FATBUF
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pop ax ; restore first cluster number
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push ds ; store LOADSEG
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next_clust: stosw ; store cluster number
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mov si, ax ; SI = cluster number
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%ifdef ISFAT12
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; This is a FAT-12 disk.
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fat_12: add si, si ; multiply cluster number by 3...
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add si, ax
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shr si, 1 ; ...and divide by 2
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lodsw
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; If the cluster number was even, the cluster value is now in
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; bits 0-11 of AX. If the cluster number was odd, the cluster
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; value is in bits 4-15, and must be shifted right 4 bits. If
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; the number was odd, CF was set in the last shift instruction.
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jnc fat_even
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mov cl, 4
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shr ax, cl
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fat_even: and ah, 0x0f ; mask off the highest 4 bits
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cmp ax, 0x0ff8 ; check for EOF
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jb next_clust ; continue if not EOF
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%endif
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%ifdef ISFAT16
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; This is a FAT-16 disk. The maximal size of a 16-bit FAT
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; is 128 kb, so it may not fit within a single 64 kb segment.
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fat_16: mov dx, LOADSEG
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add si, si ; multiply cluster number by two
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jnc first_half ; if overflow...
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add dh, 0x10 ; ...add 64 kb to segment value
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first_half: mov ds, dx ; DS:SI = pointer to next cluster
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lodsw ; AX = next cluster
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cmp ax, 0xfff8 ; >= FFF8 = 16-bit EOF
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jb next_clust ; continue if not EOF
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%endif
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finished: ; Mark end of FAT chain with 0, so we have a single
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; EOF marker for both FAT-12 and FAT-16 systems.
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xor ax, ax
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stosw
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push cs
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pop ds
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; loadFile: Loads the file into memory, one cluster at a time.
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pop es ; set ES:BX to load address 70:0
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xor bx, bx
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lea si, [CLUSTLIST] ; set DS:SI to the FAT chain
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cluster_next: lodsw ; AX = next cluster to read
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or ax, ax ; EOF?
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jne load_next ; no, continue
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; dl set to drive by readDisk
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mov ch, [bsMedia] ; ch set to media id
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mov ax, [data_start+2] ; ax:bx set to 1st data sector
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mov bx, [data_start] ;
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jmp LOADSEG:0000 ; yes, pass control to kernel
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load_next: dec ax ; cluster numbers start with 2
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dec ax
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mov di, word [bsSecPerClust]
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and di, 0xff ; DI = sectors per cluster
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mul di
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add ax, [data_start]
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adc dx, [data_start+2] ; DX:AX = first sector to read
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call readDisk
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jmp short cluster_next
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; shows text after the call to this function.
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show: pop si
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lodsb ; get character
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push si ; stack up potential return address
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mov ah,0x0E ; show character
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int 0x10 ; via "TTY" mode
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cmp al,'.' ; end of string?
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jne show ; until done
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ret
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; failed to boot
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boot_error:
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%ifdef LOOPONERR
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jmp boot_error
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%else
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call show
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; db "Error! Hit a key to reboot."
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db "Err."
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xor ah,ah
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int 0x13 ; reset floppy
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int 0x16 ; wait for a key
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int 0x19 ; reboot the machine
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%endif
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; readDisk: Reads a number of sectors into memory.
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;
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; Call with: DX:AX = 32-bit DOS sector number
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; DI = number of sectors to read
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; ES:BX = destination buffer
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;
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; Returns: CF set on error
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; ES:BX points one byte after the last byte read.
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; Exits early if LBA_SEG == LOADEND.
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|
||||
readDisk: push si ; preserve cluster #
|
||||
|
||||
mov LBA_SECTOR_0,ax
|
||||
mov LBA_SECTOR_16,dx
|
||||
mov word [LBA_SEG], es
|
||||
mov word [LBA_OFF], bx
|
||||
|
||||
call show
|
||||
db "."
|
||||
read_next:
|
||||
|
||||
; initialize constants
|
||||
mov LBA_SIZE, 10h ; LBA packet is 16 bytes
|
||||
mov LBA_SECNUM,1 ; reset LBA count if error
|
||||
|
||||
; limit kernel loading to 29KB, preventing stack & boot sector being overwritten
|
||||
cmp word [LBA_SEG], LOADEND ; skip reading if past the end
|
||||
je read_skip ; of kernel file buffer
|
||||
|
||||
;******************** LBA_READ *******************************
|
||||
|
||||
; check for LBA support
|
||||
|
||||
%ifdef TRYLBAREAD
|
||||
mov ah,041h ;
|
||||
mov bx,055aah ;
|
||||
mov dl, [drive] ; BIOS drive, 0=A:, 80=C:
|
||||
test dl,dl ; don't use LBA addressing on A:
|
||||
jz read_normal_BIOS ; might be a (buggy)
|
||||
; CDROM-BOOT floppy emulation
|
||||
int 0x13
|
||||
jc read_normal_BIOS
|
||||
|
||||
shr cx,1 ; CX must have 1 bit set
|
||||
|
||||
sbb bx,0aa55h - 1 ; tests for carry (from shr) too!
|
||||
jne read_normal_BIOS
|
||||
; OK, drive seems to support LBA addressing
|
||||
lea si,[LBA_PACKET]
|
||||
; setup LBA disk block
|
||||
mov LBA_SECTOR_32,bx ; bx is 0 if extended 13h mode supported
|
||||
mov LBA_SECTOR_48,bx
|
||||
|
||||
|
||||
mov ah,042h
|
||||
jmp short do_int13_read
|
||||
%endif
|
||||
|
||||
|
||||
|
||||
read_normal_BIOS:
|
||||
|
||||
;******************** END OF LBA_READ ************************
|
||||
mov cx, LBA_SECTOR_0
|
||||
mov dx, LBA_SECTOR_16
|
||||
|
||||
;
|
||||
; translate sector number to BIOS parameters
|
||||
;
|
||||
;
|
||||
; abs = sector offset in track
|
||||
; + head * sectPerTrack offset in cylinder
|
||||
; + track * sectPerTrack * nHeads offset in platter
|
||||
;
|
||||
mov al, [sectPerTrack]
|
||||
mul byte [nHeads]
|
||||
xchg ax, cx
|
||||
; cx = nHeads * sectPerTrack <= 255*63
|
||||
; dx:ax = abs
|
||||
div cx
|
||||
; ax = track, dx = sector + head * sectPertrack
|
||||
xchg ax, dx
|
||||
; dx = track, ax = sector + head * sectPertrack
|
||||
div byte [sectPerTrack]
|
||||
; dx = track, al = head, ah = sector
|
||||
mov cx, dx
|
||||
; cx = track, al = head, ah = sector
|
||||
|
||||
; the following manipulations are necessary in order to
|
||||
; properly place parameters into registers.
|
||||
; ch = cylinder number low 8 bits
|
||||
; cl = 7-6: cylinder high two bits
|
||||
; 5-0: sector
|
||||
mov dh, al ; save head into dh for bios
|
||||
xchg ch, cl ; set cyl no low 8 bits
|
||||
ror cl, 1 ; move track high bits into
|
||||
ror cl, 1 ; bits 7-6 (assumes top = 0)
|
||||
or cl, ah ; merge sector into cylinder
|
||||
inc cx ; make sector 1-based (1-63)
|
||||
|
||||
les bx,[LBA_OFF]
|
||||
mov ax, 0x0201
|
||||
do_int13_read:
|
||||
mov dl, [drive]
|
||||
int 0x13
|
||||
|
||||
read_finished:
|
||||
%ifdef RETRYALWAYS
|
||||
jnc read_ok ; jump if no error
|
||||
xor ah, ah ; else, reset floppy
|
||||
int 0x13
|
||||
read_next_chained:
|
||||
jmp short read_next ; read the same sector again
|
||||
%else
|
||||
jc boot_error ; exit on error
|
||||
%endif
|
||||
|
||||
read_ok:
|
||||
mov ax, word [bsBytesPerSec]
|
||||
shr ax, 4 ; adjust segment pointer by increasing
|
||||
add word [LBA_SEG], ax ; by paragraphs read in (per sector)
|
||||
|
||||
add LBA_SECTOR_0, byte 1
|
||||
adc LBA_SECTOR_16, byte 0 ; DX:AX = next sector to read
|
||||
dec di ; if there is anything left to read,
|
||||
%ifdef RETRYALWAYS
|
||||
jnz read_next_chained ; continue
|
||||
%else
|
||||
jnz read_next ; continue
|
||||
%endif
|
||||
|
||||
read_skip:
|
||||
mov es, word [LBA_SEG] ; load adjusted segment value
|
||||
; clear carry: unnecessary since adc clears it
|
||||
pop si
|
||||
ret
|
||||
|
||||
times 0x01f1-$+$$ db 0
|
||||
%ifdef MSCOMPAT
|
||||
filename db "IO SYS"
|
||||
%else
|
||||
filename db "IBMBIO COM"
|
||||
%endif
|
||||
db 0,0
|
||||
|
||||
sign dw 0xAA55
|
||||
|
||||
Loading…
Reference in New Issue
Block a user