2efe4ab9f4
This should be Enhanced DR-DOS compatible. oemboot.asm contains an optimisation to save 2 bytes, by using mov instead of a lea with bp evaluating to a constant value. This was needed to fit the addition for 256 spc support. It is otherwise unrelated. The LBA detection patch offsets in SYS have also been updated to match the changed boot.asm offsets.
667 lines
27 KiB
NASM
667 lines
27 KiB
NASM
;
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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) MS-DOS. It may work with older OpenDOS/DR-DOS,
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; although the standard FreeDOS boot sector is needed with ver 7+
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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 MS-DOS up to version
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; 6.xx 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 starting (LBA) sector of cluster 2 (ie the 1st
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; data sector, which is 0x0000:0021 for FAT12)
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; ?note? IBMBIO.COM/IO.SYS may use ax:bx and cluster # stored
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; elsewhere (perhaps dir entry still at 0x50:0) to determine
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; starting sector for full loading of kernel file.
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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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; For MS-DOS >= 7 (ie Win9x DOS) the following conditions
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; must be met:
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; bp = 0x7C00, ie offset boot sector loaded at
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; [bp-4] = the starting (LBA) sector of cluster 2 (ie the 1st
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; data sector [this is the same as ax:bx for earlier versions
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; and dx:ax in Win9x boot sector]
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; The starting cluster of the kernel file is stored in
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; di for FAT 12/16 (where si is a don't care) and si:di
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; for FAT 32.
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; The values for ax,bx,cx,dx,ds and the stack do not
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; seem to be important (used by IO.SYS) and so may be any value
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; (though dx:ax=[data_start], cx=0, bx=0x0f00 on FAT12 or
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; 0x0700 on FAT32, ds=0, ss:sp=0:7b??)
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; the boot time stack may store the original int1E floppy
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; parameter table, otherwise nothing else important seems
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; stored there and I am unsure if even this value is used
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; beyond boot sector code.
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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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; |VARS | only known is 1st data sector (start of cluster 2)
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; |--------| 0000:7BFC (DS:[BP-4])
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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 contains directory entries
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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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CPU 8086 ; enable assembler warnings to limit instruction set
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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 SETROOTDIR 1 ; if defined dir entry copied to 0:500
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%define LOOPONERR 1 ; if defined on error simply loop forever
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;%define RETRYALWAYS 1 ; if defined retries read forever
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;%define WINBOOT 1 ; use win9x kernel calling conventions (name & jmp addr)
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;%define MSCOMPAT 1 ; sets default filename to MSDOS IO.SYS
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%ifdef WINBOOT ; if set also change from PC-DOS to
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%ifndef MSCOMPAT ; kernel name to MS-DOS kernel name
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%define MSCOMPAT
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%endif
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%endif
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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 0x7C00-0x7700 ; 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 first_cluster PARAMS+0x0a ; starting cluster of kernel file
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%define data_start bp-4 ; first data sector (win9x expects here)
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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-$+$$ db 0
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;
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; Instead of zero-fill,
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; initialize BPB with values suitable for a 1440 K floppy
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;
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db 'IBM 5.0' ; OEM label
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dw 512 ; bytes per sector
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db 1 ; sectors per cluster
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dw 1 ; reserved sectors
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db 2 ; number of FATs
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dw 224 ; root directory entries
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dw 80 * 36 ; total sectors on disk
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db 0xF0 ; media descriptor
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dw 9 ; sectors per 1 FAT copy
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dw 18 ; sectors per track
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dw 2 ; number of heads
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dd 0 ; hidden sectors
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dd 0 ; big total sectors
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db 0 ; boot unit
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db 0 ; reserved
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db 0x29 ; extended boot record id
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dd 0x12345678 ; volume serial number
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db 'NO NAME '; volume label
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times 36h - ($ - $$) db 0
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; The filesystem ID is used by lDOS's instsect (by ecm)
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; by default to validate that the filesystem matches.
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%ifdef ISFAT12
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db "FAT12" ; filesystem id
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%ifdef ISFAT16
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%error Must select one FS
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%endif
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%elifdef ISFAT16
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db "FAT16"
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%else
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%error Must select one FS
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%endif
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times 3Eh - ($ - $$) db 32
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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-4] ; for DOS <7 this may be [bp]
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; For compatibility, diskette parameter vector updated.
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; lea di [bp+0x3E] ; use 7c3e([bp+3e]) for PC-DOS,
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; ;lea di [bp] ; but 7c00([bp]) for DR-DOS 7 bug
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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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; push ds ; store original 1eh pointer at stack top
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; push si ; so can restore later if needed
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;
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; Copy table to new location
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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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;
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; Note: make desired changes to table here
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;
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; Update int1E to new location
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; mov [bx+2], 0 ; set to 0:bp or 0:bp+3e as appropriate
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; mov word [bx], 0x7c3e ; (use 0x7c00 for DR-DOS)
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sti ; enable interrupts
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; If updated floppy parameter table then must notify BIOS
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; Otherwise a reset should not be needed here.
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; int 0x13 ; reset drive (AX=0)
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;
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; Note: some BIOS implementations may not correctly pass drive number
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; in DL, however we work around this in SYS.COM by NOP'ing out the use of DL
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; (formerly we checked for [drive]==0xff; update sys.c if code moves)
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;
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mov [drive], dl ; rely on BIOS drive number in DL
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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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mov 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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mov 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 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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jmp boot_error
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ffDone:
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mov [first_cluster], 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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mov di, ROOTDIR ; es:di = 0:0500
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mov cx, 32 ; limit to this 1 entry (rest don't matter)
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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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mov ax, [first_cluster] ; 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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mov cl, 4 ; always initialise shift counter
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jc fat_odd ; is odd, only shift down -->
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shl ax, cl ; shift up (effectively masks off
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; the highest 4 bits)
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fat_odd:
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shr ax, cl
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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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mov di, [first_cluster] ; set di (si:di on FAT32) to starting cluster #
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%ifdef WINBOOT
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jmp LOADSEG:0x0200 ; yes, pass control to kernel
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%else
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jmp LOADSEG:0000 ; yes, pass control to kernel
|
|
%endif
|
|
|
|
|
|
; failed to boot
|
|
boot_error:
|
|
call show
|
|
; db "Error! Hit a key to reboot.",0
|
|
db "):",0
|
|
%ifdef LOOPONERR
|
|
jmp $
|
|
%else
|
|
|
|
; Note: should restore floppy paramater table address at int 0x1E
|
|
xor ah,ah
|
|
int 0x13 ; reset floppy
|
|
int 0x16 ; wait for a key
|
|
int 0x19 ; reboot the machine
|
|
%endif
|
|
|
|
|
|
load_next: dec ax ; cluster numbers start with 2
|
|
dec ax
|
|
|
|
mov di, word [bsSecPerClust]
|
|
dec di ; minus one if 256 spc
|
|
and di, 0xff ; DI = sectors per cluster - 1
|
|
inc di ; = spc
|
|
mul di
|
|
add ax, [data_start]
|
|
adc dx, [data_start+2] ; DX:AX = first sector to read
|
|
call readDisk
|
|
jmp short cluster_next
|
|
|
|
|
|
; shows text after the call to this function.
|
|
|
|
show.do_show:
|
|
mov ah, 0Eh ; show character
|
|
int 10h ; via "TTY" mode
|
|
show: pop si
|
|
lodsb ; get character
|
|
push si ; stack up potential return address
|
|
cmp al, 0 ; end of string?
|
|
jne .do_show ; until done
|
|
ret
|
|
|
|
|
|
; readDisk: Reads a number of sectors into memory.
|
|
;
|
|
; Call with: DX:AX = 32-bit DOS sector number
|
|
; DI = number of sectors to read
|
|
; ES:BX = destination buffer
|
|
;
|
|
; Returns: CF set on error
|
|
; ES:BX points one byte after the last byte read.
|
|
; Exits early if LBA_SEG == LOADEND.
|
|
|
|
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 ".",0
|
|
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]
|
|
mov cl, 4 ; adjust segment pointer by increasing
|
|
shr ax, cl
|
|
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
|
|
|