; ; bootauto: Auto-boot version of BOOTMENU program ; by Gordon W. Ross, Aug 1990 ; modified by dave safford for simple installation ; 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 prompt doit: mov si, offset prompt + CODEORG call puts ; Search partition table for last active entry ; store in [bp-2], and decativate all ptable entries mov ax,0; mov dh,0; search: call addr_pt ; si = & ptable[AL] mov DL,[si] cmp DL,80h jnz inactive ; mov [bp-2],ax ; Save the ptable array index mov [si],ah ; make inactive mov dh,1 ; signal that active partition found inactive: inc al cmp al,04 jb search cmp dh,0 ; Was an active partition not found? jnz found ; xor ax,ax; mov [bp-2], ax; default to partition 1 found: ; Found a partition marked active. ; Delay while watching for key press (2 sec.) ; Get start time, compute end time. 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 select ; 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 ax,[bp-2] ; ptable index jmp boot ; read user selection select: ; Read a key and convert it to a number mov ah,0 int 16h sub al,'1' cmp al,04 jnb doit ; 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 ; Invlidate all other partitions -- execpt DOS-12 or DOS-16 push si; mov ax,6200H; makes ah dec 98, al zero invalidate: ; call addr_pt ; si = & ptable[AL] ; mov DL,[si] ; cmp DL,80h ; jz cont; Active partition; don't invalidate this one ; mov DL,[si+4]; System id ; cmp DL,1h; DOS-12 partition; don't invalidate ; jz cont ; cmp DL,4h; DOS-16 partition; don't invalidate ; jz cont ; mov [si+4],ah ; invalidate, by changing sysid to dec 98 ; cont: ; inc al ; cmp al,04 ; jb invalidate ; pop si; 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 doit ;************************************************************* ; 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 ;********************************************************** 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 + 1AAh ; pnames db 20 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