2000-05-06 21:34:20 +02:00
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;
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; File:
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; boot.asm
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; Description:
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; DOS-C boot
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;
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; Copyright (c) 1997;
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; Svante Frey
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; All Rights Reserved
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;
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; This file is part of DOS-C.
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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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2000-05-25 22:56:23 +02:00
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;
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2000-05-06 21:34:20 +02:00
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; $Log$
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2001-04-29 19:34:41 +02:00
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; Revision 1.4 2001/04/29 17:34:39 bartoldeman
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; A new SYS.COM/config.sys single stepping/console output/misc fixes.
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;
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2000-05-25 22:56:23 +02:00
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; Revision 1.3 2000/05/25 20:56:19 jimtabor
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; Fixed project history
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;
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2000-05-11 05:57:10 +02:00
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; Revision 1.2 2000/05/11 03:56:42 jimtabor
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; Clean up and Release
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2000-05-06 21:34:20 +02:00
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;
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2000-05-25 22:56:23 +02:00
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; Revision 1.1.1.1 2000/05/06 19:34:53 jhall1
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; The FreeDOS Kernel. A DOS kernel that aims to be 100% compatible with
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; MS-DOS. Distributed under the GNU GPL.
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;
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2000-05-06 21:34:20 +02:00
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; Revision 1.12 1999/09/25 06:42:18 jprice
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; Optimize boot loader. Documentation.
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;
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; Revision 1.11 1999/09/24 19:04:55 jprice
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; Added changes recommended by Jens Horstmeier
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; to make their bootable CD work.
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;
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; Revision 1.10 1999/09/23 04:39:02 jprice
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; *** empty log message ***
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;
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; Revision 1.7 1999/04/23 03:43:46 jprice
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; Ported to NASM by ror4
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;
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; Revision 1.6 1999/04/17 19:14:03 jprice
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; Fixed multi-sector code
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;
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; Revision 1.5 1999/04/17 06:23:26 jprice
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; Changed so multi-sector IO is optional.
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;
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; Revision 1.4 1999/04/13 15:52:22 jprice
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; Moves boot sector to top of mem
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;
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; Revision 1.3 1999/04/06 22:53:36 jprice
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; Put back code to read multiple sectors at a time.
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;
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; Revision 1.2 1999/04/01 07:23:20 jprice
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; New boot loader
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;
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; Revision 1.1.1.1 1999/03/29 15:39:39 jprice
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; New version without IPL.SYS
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;
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; Revision 1.3 1999/03/02 06:57:14 jprice
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; Added entry address for more recent versions of TLINK
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;
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; Revision 1.2 1999/01/21 05:03:58 jprice
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; Formating.
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;
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; Revision 1.1.1.1 1999/01/20 05:51:00 jprice
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; Imported sources
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;
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;
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; Rev 1.5 10 Jan 1997 4:58:06 patv
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; Corrected copyright
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;
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; Rev 1.4 10 Jan 1997 4:52:50 patv
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; Re-written to support C drive and eliminate restrictions on IPL.SYS
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;
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; Rev 1.3 29 Aug 1996 13:06:50 patv
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; Bug fixes for v0.91b
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;
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; Rev 1.2 01 Sep 1995 17:56:44 patv
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; First GPL release.
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;
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; Rev 1.1 30 Jul 1995 20:37:38 patv
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; Initialized stack before use.
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;
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; Rev 1.0 02 Jul 1995 10:57:52 patv
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; Initial revision.
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;
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; +--------+
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; | |
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; | |
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; |--------| 4000:0000
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; | |
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; | FAT |
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; | |
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; |--------| 2000:0000
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; |BOOT SEC|
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; |RELOCATE|
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; |--------| 1FE0:0000
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; | |
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; | |
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; | |
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; | |
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; |--------|
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; |BOOT SEC|
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; |ORIGIN | 07C0:0000
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; |--------|
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; | |
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; | |
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; | |
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; |--------|
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; |KERNEL |
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; |LOADED |
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; |--------| 0060:0000
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; | |
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; +--------+
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;%define ISFAT12 1
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;%define ISFAT16 1
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;%define CALCPARAMS 1
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;%define MULTI_SEC_READ 1
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segment .text
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%define BASE 0x7c00
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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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%define LOADSEG 0x0060
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%define FATBUF 0x2000 ; offset of temporary buffer for FAT
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; chain
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; Some extra variables
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;%define StoreSI bp+3h ;temp store
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; To save space, functions that are just called once are
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; implemented as macros instead. Four bytes are saved by
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; avoiding the call / ret instructions.
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; GETDRIVEPARMS: Calculate start of some disk areas.
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;
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%macro GETDRIVEPARMS 0
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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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xor ah, ah
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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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mov word [root_dir_start], si
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mov word [root_dir_start+2], di
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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
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mov word [RootDirSecs], ax ; AX = sectors per root directory
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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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%endmacro
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;-----------------------------------------------------------------------
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times 0x3E-$+$$ db 0
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%define tempbuf bp+0x3E
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dw LOADSEG
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%ifdef CALCPARAMS
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%define RootDirSecs bp+0x27 ; # of sectors root dir uses
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%define fat_start bp+0x29 ; first FAT sector
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%define root_dir_start bp+0x2D ; first root directory sector
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%define data_start bp+0x31 ; first data sector
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%else
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%define RootDirSecs bp+0x40 ; # of sectors root dir uses
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dw 0
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%define fat_start bp+0x42 ; first FAT sector
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dd 0
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%define root_dir_start bp+0x46 ; first root directory sector
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dd 0
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%define data_start bp+0x4A ; first data sector
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dd 0
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%endif
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;-----------------------------------------------------------------------
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; ENTRY
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;-----------------------------------------------------------------------
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real_start: cli
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cld
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xor ax, ax
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mov ss, ax ; initialize stack
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mov ds, ax
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mov bp, 0x7c00
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lea sp, [bp-0x20]
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sti
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int 0x13 ; reset drive
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; int 0x12 ; get memory available in AX
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; mov ax, 0x01e0
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; mov cl, 6 ; move boot sector to higher memory
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; shl ax, cl
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; sub ax, 0x07e0
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mov ax, 0x1FE0
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mov es, ax
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mov si, bp
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mov di, bp
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mov cx, 0x0100
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rep movsw
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push es
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mov bx, cont
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push bx
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retf
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cont: mov ds, ax
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mov ss, ax
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mov [drive], dl ; BIOS passes drive number in DL
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call print
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db "Loading FreeDOS...",13,10,"ROOT",0
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%ifdef CALCPARAMS
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GETDRIVEPARMS
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%endif
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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 whole root directory
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; into the temporary buffer.
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mov ax, word [root_dir_start]
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mov dx, word [root_dir_start+2]
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mov di, word [RootDirSecs]
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xor bx, bx
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2001-04-29 19:34:41 +02:00
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mov word [tempbuf], LOADSEG
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2000-05-06 21:34:20 +02:00
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mov es, [tempbuf]
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call readDisk
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jc jmp_boot_error
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xor di, di
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; Search for KERNEL.SYS file name, and find start cluster.
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next_entry: mov cx, 11
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mov si, filename
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push di
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repe cmpsb
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pop di
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mov ax, [es:di+0x1A]; get cluster number from directory entry
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je ffDone
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add di, byte 0x20 ; go to next directory entry
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cmp byte [es:di], 0 ; if the first byte of the name is 0,
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jnz next_entry ; there is no more files in the directory
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jc boot_error ; fail if not found
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ffDone:
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push ax ; store first cluster number
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call print
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db " FAT",0
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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
|
|
|
|
|
; can't be larger than around 3 kb.
|
|
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|
|
;
|
|
|
|
|
; Call with: AX = first cluster in chain
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|
|
|
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|
|
; Load the complete FAT into memory. The FAT can't be larger
|
|
|
|
|
; than 128 kb, so it should fit in the temporary buffer.
|
|
|
|
|
|
|
|
|
|
mov es, [tempbuf]
|
|
|
|
|
xor bx, bx
|
|
|
|
|
mov di, [sectPerFat]
|
|
|
|
|
mov ax, word [fat_start]
|
|
|
|
|
mov dx, word [fat_start+2]
|
|
|
|
|
call readDisk
|
|
|
|
|
pop ax ; restore first cluster number
|
|
|
|
|
jmp_boot_error: jc boot_error
|
|
|
|
|
|
|
|
|
|
; Set ES:DI to the temporary storage for the FAT chain.
|
|
|
|
|
push ds
|
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|
|
push es
|
|
|
|
|
pop ds
|
|
|
|
|
pop es
|
|
|
|
|
mov di, FATBUF
|
|
|
|
|
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|
|
|
next_clust: stosw ; store cluster number
|
|
|
|
|
mov si, ax ; SI = cluster number
|
|
|
|
|
|
|
|
|
|
%ifdef ISFAT12
|
|
|
|
|
; This is a FAT-12 disk.
|
|
|
|
|
|
|
|
|
|
fat_12: add si, si ; multiply cluster number by 3...
|
|
|
|
|
add si, ax
|
|
|
|
|
shr si, 1 ; ...and divide by 2
|
|
|
|
|
lodsw
|
|
|
|
|
|
|
|
|
|
; If the cluster number was even, the cluster value is now in
|
|
|
|
|
; bits 0-11 of AX. If the cluster number was odd, the cluster
|
|
|
|
|
; value is in bits 4-15, and must be shifted right 4 bits. If
|
|
|
|
|
; the number was odd, CF was set in the last shift instruction.
|
|
|
|
|
|
|
|
|
|
jnc fat_even
|
|
|
|
|
mov cl, 4
|
|
|
|
|
shr ax, cl ; shift the cluster number
|
|
|
|
|
|
|
|
|
|
fat_even: and ah, 0x0f ; mask off the highest 4 bits
|
|
|
|
|
cmp ax, 0x0fff ; check for EOF
|
|
|
|
|
jb next_clust ; continue if not EOF
|
|
|
|
|
|
|
|
|
|
%endif
|
|
|
|
|
%ifdef ISFAT16
|
|
|
|
|
; This is a FAT-16 disk. The maximal size of a 16-bit FAT
|
|
|
|
|
; is 128 kb, so it may not fit within a single 64 kb segment.
|
|
|
|
|
|
|
|
|
|
fat_16: mov dx, [tempbuf]
|
|
|
|
|
add si, si ; multiply cluster number by two
|
|
|
|
|
jnc first_half ; if overflow...
|
|
|
|
|
add dh, 0x10 ; ...add 64 kb to segment value
|
|
|
|
|
|
|
|
|
|
first_half: mov ds, dx ; DS:SI = pointer to next cluster
|
|
|
|
|
lodsw ; AX = next cluster
|
|
|
|
|
|
|
|
|
|
cmp ax, 0xfff8 ; >= FFF8 = 16-bit EOF
|
|
|
|
|
jb next_clust ; continue if not EOF
|
|
|
|
|
%endif
|
|
|
|
|
|
|
|
|
|
finished: ; Mark end of FAT chain with 0, so we have a single
|
|
|
|
|
; EOF marker for both FAT-12 and FAT-16 systems.
|
|
|
|
|
|
|
|
|
|
xor ax, ax
|
|
|
|
|
stosw
|
|
|
|
|
|
|
|
|
|
push cs
|
|
|
|
|
pop ds
|
|
|
|
|
|
|
|
|
|
call print
|
|
|
|
|
db " KERNEL",0
|
|
|
|
|
|
|
|
|
|
; loadFile: Loads the file into memory, one cluster at a time.
|
|
|
|
|
|
|
|
|
|
mov es, [tempbuf] ; set ES:BX to load address
|
|
|
|
|
xor bx, bx
|
|
|
|
|
|
|
|
|
|
mov si, FATBUF ; set DS:SI to the FAT chain
|
|
|
|
|
|
|
|
|
|
cluster_next: lodsw ; AX = next cluster to read
|
|
|
|
|
or ax, ax ; if EOF...
|
|
|
|
|
je boot_success ; ...boot was successful
|
|
|
|
|
|
|
|
|
|
dec ax ; cluster numbers start with 2
|
|
|
|
|
dec ax
|
|
|
|
|
|
|
|
|
|
mov di, word [bsSecPerClust]
|
|
|
|
|
and di, 0xff ; DI = sectors per cluster
|
|
|
|
|
mul di
|
|
|
|
|
add ax, [data_start]
|
|
|
|
|
adc dx, [data_start+2] ; DX:AX = first sector to read
|
|
|
|
|
call readDisk
|
|
|
|
|
jnc cluster_next
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
boot_error: call print
|
|
|
|
|
db 13,10,"BOOT error!",13,10,0
|
|
|
|
|
|
|
|
|
|
xor ah,ah
|
|
|
|
|
int 0x16 ; wait for a key
|
|
|
|
|
int 0x19 ; reboot the machine
|
|
|
|
|
|
|
|
|
|
boot_success: call print
|
|
|
|
|
db " GO!",13,10,0
|
|
|
|
|
mov bl, [drive]
|
|
|
|
|
jmp word LOADSEG:0
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
; prints text after call to this function.
|
|
|
|
|
|
|
|
|
|
print: pop si ; this is the first character
|
|
|
|
|
xor bx, bx ; video page 0
|
|
|
|
|
mov ah, 0x0E ; else print it
|
|
|
|
|
print1: lodsb ; get token
|
|
|
|
|
cmp al, 0 ; end of string?
|
|
|
|
|
je print2 ; if so, exit
|
|
|
|
|
int 0x10 ; via TTY mode
|
|
|
|
|
jmp short print1 ; until done
|
|
|
|
|
print2: push si ; stack up return address
|
|
|
|
|
ret ; and jump to it
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
; 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
|
|
|
|
|
; ES must be 64k aligned (1000h, 2000h etc).
|
|
|
|
|
;
|
|
|
|
|
; Returns: CF set on error
|
|
|
|
|
; ES:BX points one byte after the last byte read.
|
|
|
|
|
|
|
|
|
|
readDisk: push si
|
|
|
|
|
read_next: push dx
|
|
|
|
|
push ax
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; translate sector number to BIOS parameters
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; abs = sector offset in track
|
|
|
|
|
; + head * sectPerTrack offset in cylinder
|
|
|
|
|
; + track * sectPerTrack * nHeads offset in platter
|
|
|
|
|
;
|
|
|
|
|
; t1 = abs / sectPerTrack (ax has t1)
|
|
|
|
|
; sector = abs mod sectPerTrack (cx has sector)
|
|
|
|
|
;
|
|
|
|
|
div word [sectPerTrack]
|
|
|
|
|
mov cx, dx
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; t1 = head + track * nHeads
|
|
|
|
|
;
|
|
|
|
|
; track = t1 / nHeads (ax has track)
|
|
|
|
|
; head = t1 mod nHeads (dl has head)
|
|
|
|
|
;
|
|
|
|
|
xor dx, dx
|
|
|
|
|
div word [nHeads]
|
|
|
|
|
|
|
|
|
|
; 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, dl ; save head into dh for bios
|
|
|
|
|
ror ah, 1 ; move track high bits into
|
|
|
|
|
ror ah, 1 ; bits 7-6 (assumes top = 0)
|
|
|
|
|
xchg al, ah ; swap for later
|
|
|
|
|
mov dl, byte [sectPerTrack]
|
|
|
|
|
sub dl, cl
|
|
|
|
|
inc cl ; sector offset from 1
|
|
|
|
|
or cx, ax ; merge cylinder into sector
|
|
|
|
|
mov al, dl ; al has # of sectors left
|
|
|
|
|
|
|
|
|
|
%ifdef MULTI_SEC_READ
|
|
|
|
|
; Calculate how many sectors can be transfered in this read
|
|
|
|
|
; due to dma boundary conditions.
|
|
|
|
|
push dx
|
|
|
|
|
|
|
|
|
|
mov si, di ; temp register save
|
|
|
|
|
; this computes remaining bytes because of modulo 65536
|
|
|
|
|
; nature of dma boundary condition
|
|
|
|
|
mov ax, bx ; get offset pointer
|
|
|
|
|
neg ax ; and convert to bytes
|
|
|
|
|
jz ax_min_1 ; started at seg:0, skip ahead
|
|
|
|
|
|
|
|
|
|
xor dx, dx ; convert to sectors
|
|
|
|
|
div word [bsBytesPerSec]
|
|
|
|
|
|
|
|
|
|
cmp ax, di ; check remainder vs. asked
|
|
|
|
|
jb ax_min_1 ; less, skip ahead
|
|
|
|
|
mov si, ax ; transfer only what we can
|
|
|
|
|
|
|
|
|
|
ax_min_1: pop dx
|
|
|
|
|
|
|
|
|
|
; Check that request sectors do not exceed track boundary
|
|
|
|
|
mov si, [sectPerTrack]
|
|
|
|
|
inc si
|
|
|
|
|
mov ax, cx ; get the sector/cyl byte
|
|
|
|
|
and ax, 0x3f ; and mask out sector
|
|
|
|
|
sub si, ax ; si has how many we can read
|
|
|
|
|
mov ax, di
|
|
|
|
|
cmp si, di ; see if asked <= available
|
|
|
|
|
jge ax_min_2
|
|
|
|
|
mov ax, si ; get what can be xfered
|
|
|
|
|
|
|
|
|
|
ax_min_2: push ax
|
|
|
|
|
mov ah, 2
|
|
|
|
|
mov dl, [drive]
|
|
|
|
|
int 0x13
|
|
|
|
|
pop ax
|
|
|
|
|
%else
|
|
|
|
|
mov ax, 0x0201
|
|
|
|
|
mov dl, [drive]
|
|
|
|
|
int 0x13
|
|
|
|
|
%endif
|
|
|
|
|
jnc read_ok ; jump if no error
|
|
|
|
|
xor ah, ah ; else, reset floppy
|
|
|
|
|
int 0x13
|
|
|
|
|
pop ax
|
|
|
|
|
pop dx ; and...
|
|
|
|
|
jmp short read_next ; read the same sector again
|
|
|
|
|
|
|
|
|
|
read_ok:
|
|
|
|
|
%ifdef MULTI_SEC_READ
|
|
|
|
|
mul word [bsBytesPerSec] ; add number of bytes read to BX
|
|
|
|
|
add bx, ax
|
|
|
|
|
%else
|
|
|
|
|
add bx, word [bsBytesPerSec]
|
|
|
|
|
%endif
|
|
|
|
|
jnc no_incr_es ; if overflow...
|
|
|
|
|
|
|
|
|
|
mov ax, es
|
|
|
|
|
add ah, 0x10 ; ...add 1000h to ES
|
|
|
|
|
mov es, ax
|
|
|
|
|
|
|
|
|
|
no_incr_es: pop ax
|
|
|
|
|
pop dx ; DX:AX = last sector number
|
|
|
|
|
|
|
|
|
|
%ifdef MULTI_SEC_READ
|
|
|
|
|
add ax, si
|
|
|
|
|
adc dx, byte 0 ; DX:AX = next sector to read
|
|
|
|
|
sub di,si ; if there is anything left to read,
|
|
|
|
|
jg read_next ; continue
|
|
|
|
|
%else
|
|
|
|
|
add ax, 1
|
|
|
|
|
adc dx, byte 0 ; DX:AX = next sector to read
|
|
|
|
|
dec di ; if there is anything left to read,
|
|
|
|
|
jnz read_next ; continue
|
|
|
|
|
%endif
|
|
|
|
|
|
|
|
|
|
clc
|
|
|
|
|
pop si
|
|
|
|
|
ret
|
|
|
|
|
|
|
|
|
|
filename db "KERNEL SYS"
|
|
|
|
|
|
|
|
|
|
times 0x01fe-$+$$ db 0
|
|
|
|
|
|
|
|
|
|
sign dw 0xAA55
|
