hi every body
is there any body 2 help me to create a boot disk with assembly
help me plz
send ur comment 4 me 2 my email : em_moon1981@yahoo.com;)
em_moon1981 0 Newbie Poster
mathematician 0 Junior Poster
;0-10 File name (8 bytes) with extension (3 bytes)
;11 Attribute - a bitvector. Bit 0: read only. Bit 1: hidden.
; Bit 2: system file. Bit 3: volume label. Bit 4: subdirectory.
; Bit 5: archive. Bits 6-7: unused.
;12-21 Reserved (see below)
;22-23 Time (5/6/5 bits, for hour/minutes/doubleseconds)
;24-25 Date (7/4/5 bits, for year-since-1980/month/day)
;26-27 Starting cluster (0 for an empty file)
;28-31 Filesize in bytes
.586
text segment word 'code'
assume cs:text, ds:text
org 7C00h
jmp short ldr
boot proc
db ? ;byte not needed for short jump
OEMname db 'OEM NAME'
SecSize dw 512
ClustSize db 1
reserved dw 1
FATCnt db 2
RootEntries dw 224 ;max entries in root directory
unused1 dw ?
mdb db 0F0h
FATSize dw 9
SecsPerTrk dw 18
heads dw 2
hidden dd 10 ;sectors reserved for boot loader (5120 bytes available)
unused2 dd 0
drive db 0
unused3 db 0
signature db 29h
SerNum dd 03C9A71BFh
VolumeLabel db 'NO NAME '
db 'FAT12 '
ldr:
cli
xor ax,ax
mov cs,ax
mov ds,ax ;initialise segment registers
mov ss,ax
mov es,ax
mov sp, 0fffeh ;set up stack
sti
mov ax, FATSize ;load sectors per track
mov bh, FATCnt
mul bh ;calculate number of FAT sectors
add ax, reserved ;add on boot sector(s)
inc ax ;first sector of root directory
push ax
pop cx ;cl = first sector to read, ch = track 0
push cx ;save sector address of root directory
xor dh,dh ;dh = head 0
mov dl, drive ;load drive number
mov bx, 8000H ;es:bx -> buffer on DMA boundary
mov ax, 201H ;read first sector of root directory into memory
int 13h
jc BadTrk0 ;jump to error handler if read failed
mov si, 8000H ;ds:si -> first directory entry
lea di, osldr ;es:di -> loader's filename
mov cx, 11
repe cmpsb ;is loader present?
je ldr_found ;if so, skip error handler
lea si, errmsg2 ;ds:si -> non system disk message
call disp ;display message
lea si, errmsg10
call disp
jmp short reboot ;reboot computer
ldr_found:
mov ax, RootEntries
shr ax, 4 ;ax = number of root directory sectors
pop cx ;pop seg address of root directory & track number
add cl,al ;cl = first sector after root directory
cmp cl, byte ptr SecsPerTrk ;isw cl > number of sectors on track?
jna la1 ;no - so no adjustment necessary
sub cl, byte ptr SecsPerTrk ;sector number for track 0, head 1
xor dh, 1 ;toggle head number
la1:
call read64k ;read loader into memory
jnc ldr_read_ok ;skip error handler if read was successful
BadTrk0:
lea si, errmsg1 ;ds:si -> error message
call disp ;display message
lea si, errmsg10
call disp
reboot:
xor ah,ah ;wait for keystroke
int 16h
mov bx,472H ;0:472 = address of boot status word
mov word ptr [ bx ], 1234H ;skip POST test
int 19h ;reboot
ldr_read_ok:
jmp ldr_addr ;jump to osldr
osldr db 'osldr sys'
errmsg1 db 'Bad track 0 - Disk unusable.', 0dh, 0ah, 0
errmsg2 db 'Not a system disk', 0dh, 0ah, 0
errmsg10 db 'Strike any key', 0
ldr_addr dd 8000H
boot endp
disp proc
nextChar:
xor bh,bh ;page number
lodsb ;load next character
or al,al ;end of string?
jz EndDisp ;if so jump out of loop
mov ah, 0Eh ;display character
int 10h
jmp short nextChar ;next character
EndDisp:
ret
disp endp
read64k proc near
;dl = drive
;dh = head
;cl = sector
;ch = track
;bx -> buffer on DMA boundary
mov si,cx ;save sector and track numbers
mov cx, 16 ;16 * 4096 byte pages = 64kb
nextPage:
xchg cx,si ;cx = sector and track numbers, si = loop count
call readPage ;read 4096 byte page into memory
jc read64kEnd
xchg si,cx ;si = returned sector and track numbers, cx = loop count
loop nextPage ;read next page
clc
read64kEnd:
ret
read64k endp
readPage proc near
;dl = drive
;dh = head
;cl = sector
;ch = track
;bx -> buffer on DMA boundary
push bx
push cx
push dx
mov ax, 8 ;8 sectors = 4096 byte DMA page
push cx ;save sector and track number
add cl,al ;calculate end sector number
cmp cl, byte ptr SecsPerTrk
pop cx ;past end of track?
jna SameTrk ;no - so skip special code
mov ax, SecsPerTrk ;load al with number of sectors per track
sub al,cl
inc ax ;ax = number of sectors to read
push ax
push bx
push cx
push dx
mov ah, 2 ;read sectors into buffer
int 13h
pop dx
pop cx
pop bx
pop ax ;ax = number of sectors read
jnc la3 ;skip error handler if carry clear
la4:
add sp, 8 ;pop pushed registers
stc ;flag error
ret ;return to caller
la3:
push ax
shl ax, 9 ;ax = number of bytes read
add bx,ax ;update buffer pointer ready for next read
pop ax
sub al, 8
neg al ;ax = number of remaining sectors to read
mov cl, 1 ;starting with sector 1
xor dh, 1 ;toggle head number
jnz SameTrk ;jump if not back with head 0
inc ch ;otherwise increment track number
SameTrk:
mov ah, 2 ;complete read
int 13h
jc la4 ;return with carry set upon error
pop dx
pop cx
pop bx
add bx, 4096 ;increment bx by number of bytes in page
add cl, 8 ;increment starting sector by eight
cmp cl, byte ptr SecsPerTrk ;pased end of track?
jna la2 ;no - so skip handler
sub cl, byte ptr SecsPerTrk
xor dh, 1 ;toggle head number
jnz la2 ;if head != 0 do not increment track number
inc ch ;new track number
la2:
clc ;no error
ret
readPage endp
dw 0, 55AAH
text ends
endChances are you wiould need a utility to strip off the first 7C00H bytes after compiling and linking it. (Not yet tested or debugged by the way.)
mathematician 0 Junior Poster
On closer inspection, it's not exactly short of bugs.
Garni 0 Newbie Poster
hi every body
is there any body 2 help me to create a boot disk with assembly
help me plz
send ur comment 4 me 2 my email : em_moon1981@yahoo.com;)
please use this link http://perso.orange.fr/pierrelib/bootstrap/VnutZ_Bootstrap_Tutorial.html to find more about boot loader.
get back to me if u have any doubt on this article.
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