www.pudn.com > bootmenu.zip > BOOTAUTO.ASM
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; bootauto: Auto-boot version of BOOTMENU program
; by Gordon W. Ross, Aug 1990
;
; See the file bootmenu.doc for user instructions.
;
; The following is an outline of the program:
;
; Relocate self from 0x7C00 to 0x0600
; Display message "Booting from HD0,"
; Search partition table for an active entry
; If an active partition is found,
; Delay while watching for key press (5 sec.)
; If (key pressed) GOTO menu:
; Else GOTO boot:
; EndIf
; Else (no active partition)
; menu: Display partition menu
; Prompt for and read user selection
; EndIf
; boot: Boot from the selected partition:
; (was selected by user, or was active)
; Read first sector of selected partition into 0x7c00
; Verify good second-stage boot sector (magic word)
; Set-up correct register values and jump to it.
; If (Errors during boot) { complain; GOTO menu: }
;
DELAY equ 5*18 ; in ticks (1/18 sec.)
CODEORG equ 0600h ; offset of this code in code seg
; All values computed from offsets in codeseg need to be
; adjusted by adding CODEORG to each. The obvious method,
; using "org CODEORG" causes MASM/LINK to fill in the space.
codeseg segment
assume cs:codeseg, ds:codeseg
; Initial program entry point
; (Assembler is told this is at offset zero.)
main:
; Set up the stack
xor ax,ax
mov si,7C00h ; just before load location
cli
mov ss,ax
mov sp,si
sti
; Relocate this code from 0:7C00h to 0:CODEORG
mov ds,ax
mov es,ax
mov si,7C00h ; where this program is initially loaded
mov di,CODEORG
mov cx,0100h
cld
rep movsw
; Jump to relocated code (0:CODEORG)
jmp far ptr begin1
begin equ $
mov bp,sp ; frame pointer = 0x7C00
sub sp,4
; 2 words of local storage:
; [bp-2] = ptable index [0-3]
; [bp-4] = temporary value
; Display message "Boot device: HD0"
mov si, offset bootdev + CODEORG
call puts
; Search partition table for an active entry
mov al,0
search:
call addr_pt ; si = & ptable[AL]
mov DL,[si]
cmp DL,80h
jz found
inc al
cmp al,04
jb search
; Active partition not found
jmp menu
found: ; Found a partition marked active.
mov [bp-2],ax ; Save the ptable array index
; Delay while watching for key press (2 sec.)
; Get start time, compute end time.
mov ah,00
int 1Ah ; BIOS get time of day
add dx, DELAY ; compute end time
mov [bp-4],dx ; save expiration time
; Check for key press
waitkey:
mov ah,1
int 16h ; BIOS Keyboard
jnz menu ; key pressed
; Check for expiration of delay
mov ah,00
int 1Ah ; BIOS get time of day
sub dx,[bp-4]
js waitkey ; delay not expired
; Delay has expired, so boot the active partition
mov al,','
call putc
mov ax,[bp-2] ; ptable index
; the index and newline are printed later
jmp boot
; Display partition menu
menu:
mov ah,1 ; flush input
int 16h
jz fl_done
mov ah,0
int 16h
jmp menu
fl_done:
; Print partition menu from name table
call putnl ; print newline
mov si, offset pnames ; no org fix-up here
mov al, '1'
prname:
push si
push ax
call putc
mov al,' '
call putc
mov cx,8 ; maximum name length
call putn
call putnl
pop ax
pop si
add si,8
inc al
cmp al,'4'
jbe prname
; Prompt for and read user selection
select:
call putnl
mov si, offset prompt + CODEORG
call puts
; Read a key and convert it to a number
mov ah,0
int 16h
sub al,'1'
cmp al,04
jnb select
; The key and a newline are printed below
boot:
; Boot from the selected partition.
; On entry to this section: AL = index of ptable element
; get address of ptable element
call addr_pt ; si = & ptable[AL]
; print the parition index and a newline
add al,'1'
call putc
call putnl
; Check for valid system ID (non-zero)
mov al,[si+4]
cmp al,0
jnz id_ok
mov si, offset msgempty + CODEORG
jmp error
id_ok:
; Read first sector of selected partition into 0x7c00
; Also, mark this entry active (in RAM only) in case the
; secondary boot program looks at it (which it may).
mov al,80h ; active flag
mov [si], al
mov cx,5 ; retry count
retry: push cx
mov dx,[si] ; drive, head
mov cx,[si+2] ; cyl, sector
mov bx,7C00h ; destination (es=0)
mov ax,0201h ; BIOS read one sector
int 13h
jnc rd_ok
xor ax,ax ; reset disk
int 13h
pop cx
loop retry
mov si, offset msgread + CODEORG
jmp error
rd_ok: pop cx
; Check for valid magic number in secondary boot sector
mov ax, 0AA55h
assume ds:seg0 ; Actually, codeseg == seg0
cmp ax, magic2
assume ds:codeseg
jz magic_ok
mov si, offset msginvalid + CODEORG
jmp error
magic_ok:
; Make sure ds:si points to the booted partition, and
; Jump to the secondary boot program.
jmp far ptr begin2
; Jump here with si=error-message
error:
call puts
call putnl
jmp menu
;*************************************************************
; Subroutines
;*************************************************************
CR EQU 13
LF EQU 10
TAB EQU 9
putc proc near ; print char in AL
mov ah, 0Eh ; uses: ax, bx
mov bx, 07
int 10h
ret
putc endp
putnl proc near ; print a newline
mov al, CR ; uses: ax, bx
call putc
mov al, LF
call putc
ret
putnl endp
puts proc near ; print string at address SI
mov cx,80 ; Stop at null or CX chars
putn: lodsb ; uses: ax, bx, cx, si
cmp al,0
jz puts_e
push cx
call putc
pop cx
loop putn
puts_e: ret
puts endp
addr_pt proc near ; set SI = address of ptable[al]
push ax ; uses: cx (but preserves ax)
mov si, offset ptable ; no org fix-up here
mov cl,16 ; size of array element
mul cl ; ax = al * cl
add si,ax
pop ax
ret
addr_pt endp
;**********************************************************
; Strings
;**********************************************************
bootdev db "Boot device: hd0",0
prompt db "Boot partition? (1-4) ",0
msgempty db "Empty!",0
msgread db "Read error!",0
msginvalid db "Invalid!",0
org 180h ; this pads the length (it seems)
codeseg ends
; Declares some offsets in segment zero
seg0 segment at 0
org CODEORG + (offset begin - offset main)
begin1 equ $
; Here is the name table used for the partition menu.
; The accompanying fdisk program updates this table.
org CODEORG + 180h
pnames db 32 dup(?)
; The locations after 1AE are (reportedly) used by some
; Western Digital controllers in "auto-configure" mode.
; Don't put anything critical between here and ptable.
; Here is the partition table
org CODEORG + 1BEh
ptable db (4 * 16) dup(?)
; Here is where the secondary boot sector is loaded.
org 7C00h
begin2 equ $
org 7DFEh
magic2 dw ?
seg0 ends
end main