diff options
| author | joerg <joerg@FreeBSD.org> | 1995-11-05 16:02:04 +0000 |
|---|---|---|
| committer | joerg <joerg@FreeBSD.org> | 1995-11-05 16:02:04 +0000 |
| commit | a7d823cf623b0577a4b37407e2e05e46a1ae9e6f (patch) | |
| tree | 08b49f583e7d4c0790cc6b5b9af46f5d7479cd81 /usr.sbin/mkdosfs/bootcode.asm | |
| download | FreeBSD-src-a7d823cf623b0577a4b37407e2e05e46a1ae9e6f.zip FreeBSD-src-a7d823cf623b0577a4b37407e2e05e46a1ae9e6f.tar.gz | |
mkdosfs -- a tool to create an MS-DOS file system on a device or file.
Since msdosfs is part of the base system, it's not wise to rely on
something like mtools to provide this functionality.
This utility is the agreed fix for PR # misc/804 fdformat did not ...
Diffstat (limited to 'usr.sbin/mkdosfs/bootcode.asm')
| -rw-r--r-- | usr.sbin/mkdosfs/bootcode.asm | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/usr.sbin/mkdosfs/bootcode.asm b/usr.sbin/mkdosfs/bootcode.asm new file mode 100644 index 0000000..9213cba --- /dev/null +++ b/usr.sbin/mkdosfs/bootcode.asm @@ -0,0 +1,102 @@ +;;; Hello emacs, this looks like -*- asm -*- code, doesn't it? +;;; +;;; This forms a simple dummy boot program for use with a tool to +;;; format DOS floppies. All it does is displaying a message, and +;;; recover gracefully by re-initializing the CPU. +;;; +;;; Written by Joerg Wunsch, Dresden. Placed in the public domain. +;;; This software is provided as is, neither kind of warranty applies. +;;; Use at your own risk. +;;; +;;; (This is written in as86 syntax. as86 is part of Bruce Evans' +;;; bcc package.) +;;; +;;; $Id$ +;;; +;;; This code must be linked to address 0x7c00 in order to function +;;; correctly (the BIOS boot address). +;;; +;;; It's 16-bit code, and we don't care for a data segment. + use16 + .text + + entry _begin +_begin: jmp init ; jump to boot prog + nop ; historical baggage ;-) +;;; +;;; Reserve space for the "BIOS parameter block". +;;; This will be overwritten by the actual formatting routine. +;;; +bpb: .ascii "BSD 4.4" ; "OEM" name + .word 512 ; sector size + .byte 2 ; cluster size + .word 1 ; reserved sectors (just the boot sector) + .byte 2 ; FAT count + .word 112 ; # of entries in root dir + .word 1440 ; total number of sectors, MSDOS 3.3 or below + .byte 0xf9 ; "media descriptor" + .word 3 ; FAT size (sectors) + .word 9 ; sectors per track + .word 2 ; heads per cylinder + .word 0 ; hidden sectors + ;; MSDOS 4.0++ -- only valid iff total number of sectors == 0 + .word 0 ; unused + .long 0 ; total number of sectors + .short 0 ; physical drive (0, 1, ..., 0x80) %-) + .byte 0 ; "extented boot signature" + .long 0 ; volume serial number (i.e., garbage :) + .ascii " " ; label -- same as vol label in root dir + .ascii "FAT12 " ; file system ID +;;; +;;; Executable code starts here. +;;; +init: + ;; First, display our message. + mov si, *message +lp1: seg cs + movb al, [si] + inc si + testb al, al + jz lp2 ; null-terminated string + movb bl, *7 ; display with regular attribute + movb ah, *0x0e ; int 0x10, fnc 0x0e -- emulate tty + int 0x10 + jmp lp1 +lp2: xorb ah, ah ; int 0x16, fnc 0x00 -- wait for keystroke + int 0x16 + mov ax, *0x40 ; write 0x1234 to address 0x472 -- + push ax ; tell the BIOS that this is a warm boot + pop dx + mov 0x72, *0x1234 + jmpf 0xfff0,0xf000 ; jump to CPU initialization code + +message: + .byte 7 + .byte 0xc9 + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xbb, 13, 10, 0xba + .ascii " Sorry, this disc does actually not contain " + .byte 0xba, 13, 10, 0xba + .ascii " a bootable system. " + .byte 0xba, 13, 10, 0xba + .ascii " Press any key to reboot. " + .byte 0xba, 13, 10, 0xc8 + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xcd,0xcd,0xcd,0xcd,0xcd,0xcd + .byte 0xbc, 13,10 + .byte 0 + + ;; Adjust the value below after changing the length of + ;; the code above! + .space 0x1fe-0x161 ; pad to 512 bytes + + .byte 0x55, 0xaa ; yes, we are bootable (cheating :) + end +
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