; DeviatorOS bootstrap ; Credits: ; Sean Tash- programmed it in original form- 1998. ; Kenneth Garin- LOTS of code mods, reprogrammed for DeviatorOS ; Notes: ; There is a lot of work needed to be done here so that it will boot on ; many machines. So far it only boots on 9 out of 10 computers. BITS 16 ORG 0x7C00 START: JMP SHORT BEGIN NOP ; not really needed, old school style ; +-------------------------------------------------------------+ ; | Data section of boot.asm bootstrap file | ; +-------------------------------------------------------------+ bsOEM DB 'DEVIATOR' ; OEM String bsSectSize DW 512 ; Bytes per sector bsClustSize DB 1 ; Sectors per cluster bsRessect DW 1 ; # of reserved sectors bsFatCnt DB 2 ; # of fat copies bsRootSize DW 224 ; size of root directory bsTotalSect DW 2880 ; total # of sectors if < 32 meg bsMedia DB 0xF0 ; Media Descriptor bsFatSize DW 9 ; Size of each FAT bsTrackSect DW 18 ; Sectors per track bsHeadCnt DW 2 ; number of read-write heads bsHidenSect DD 0 ; number of hidden sectors bsHugeSect DD 0 ; if bsTotalSect is 0 this value is ; the number of sectors bsBootDrv DB 0 ; holds drive that the bs came from bsReserv DB 0 ; not used for anything bsBootSign DB 29h ; boot signature 29h bsVolID DD 0 ; Disk volume ID also used for temp ; sector # / # sectors to load bsVoLabel DB 'DeviatorOS ' ; Volume Label bsFSType DB 'FAT12 ' ; File System type ; +-------------------------------------------------------------+ ; | Code section of boot.asm bootstrap file | ; +-------------------------------------------------------------+ BEGIN: CLI ; disable interrupts MOV [bsBootDrv],DL ; save drive number MOV AX,0x9000 ; put stack at 0x98000 MOV SS,AX MOV SP,0x8000 MOV CX,[bsTrackSect] ; update int 1E FDC param table MOV BX,0x0078 LDS SI,[DS:BX] MOV BYTE [SI+4], CL MOV BYTE [SI+9], 0x0F MOV AX,CS MOV DS,AX ; I know its not needed, but some ; BIOS fail if DS not set the hard ; way, my Cannon 450 does anyways =( STI ; enable interrupts again PUSH DS MOV DL,[bsBootDrv] ; DL = drive we booted from XOR AX,AX INT 0x13 ; reset disk drive controller POP DS JC bootfail2 ; error resetting controller? JMP _l1 bootfail2: JMP bootfail _l1: MOV AX,0x0000 MOV ES,AX ; correct segment registers MOV DS,AX MOV SI,bootmsg ; display load message CALL putstr ; find the root directory on volume XOR AX,AX MOV AL,[bsFatCnt] ; number of FAT mirrors on disk MOV BX,[bsFatSize] ; how many sectors a FAT uses MUL BX ; AX returns FatCnt*FatSize ADD AX,WORD [bsHidenSect] ; AX=AX+HiddenSectors ADC AX,WORD [bsHidenSect+2] ; HidenSect is a double word, so... ADD AX,WORD [bsRessect] ; AX now holds the sector where the ; VTOC (Volume Table Of Contents) ; starts MOV WORD [BootSig],AX ; BootSig is used as temp to hold AX CALL checkroot ; look into VTOC in root directory ; and see if we find our kernel image XOR AX,AX ADD AX,WORD [START] ; [START] = number of sectors in root ADD AX,WORD [bsVolID] ; sector number where kernel image ; starts, but not correct value yet.. ADD AX,WORD [BootSig] ; SUB AX,2 ; correction for a mis-calc MOV CX,WORD [bsVolID+2] ; number of sectors MOV BX,0x8000 MOV ES,BX ; get ready to read sectors into mem nextsector: PUSH AX ; save registers PUSH CX PUSH DX PUSH ES XOR BX,BX ; set zero offset CALL readsect ; read a sector POP ES ; restore registers POP DX POP CX POP AX MOV BX,ES ADD BX,0x20 ; increment address 512 bytes MOV ES,BX INC AX ; read next sector LOOPNZ nextsector MOV DX,0x3F2 XOR AL,AL OUT DX,AL ; turn off floppy disk motor MOV SI,bootgood CALL putstr MOV DL,[bsBootDrv] ; don't forget our bootdrive MOV AX,0x8000 ; set segment registers and jump MOV ES,AX MOV DS,AX PUSH AX XOR AX,AX PUSH AX RETF checkroot: PUSH AX ; save registers PUSH BX PUSH CX PUSH DX PUSH SI PUSH DI MOV AX,0x8000 ; put root directory at 0x80000 MOV ES,AX MOV AX,32 ; AX = ((32*RootSize)/512) + 2 MUL WORD [bsRootSize] DIV WORD [bsSectSize] MOV CX,AX ; cx holds # of sectors in root MOV WORD [START],AX MOV AX,WORD [BootSig] ; get prev. saved loc. for root dir r1: XOR BX,BX PUSH CX ; save count PUSH AX ; save sector number PUSH ES PUSH DX CALL readsect XOR BX,BX l_1: MOV DI,BX ; set address to check from MOV CX,11 ; check 11 bytes MOV SI,FileName ; address of string to check with REPZ CMPSB JE foundit ; we found our FileName in the VTOC ADD BX,32 ; check next entry CMP BX,[bsSectSize] ; end of sector? JE l_2 JMP l_1 l_2: POP DX ; restore registers POP ES POP AX POP CX INC AX ; read next sector LOOPNZ r1 JMP bootfail foundit: POP DX ; get these off the stack POP ES POP AX POP CX MOV DI,0x1A ; get clustor # ADD DI,BX PUSH BX ; save bx for finding # of sectors MOV AX,[ES:DI] XOR BX,BX ; calculate sector # MOV BL,[bsClustSize] MUL BX ; ax holds sector # MOV WORD [bsVolID],AX POP BX ; get location of directory entry MOV DI,0x1C ADD DI,BX MOV AX,[ES:DI] ; put number of bytes in ax XOR DX,DX MOV BX,[bsClustSize] ; # of bytes / 512 DIV BX INC AX MOV WORD [bsVolID+2],AX ; save number of sectors to load POP DI ; restore registers POP SI POP DX POP CX POP BX POP AX RET ; return to caller ; +-------------------------------------------------------------+ ; | Routines used over and over in boot.asm below... | ; +-------------------------------------------------------------+ putstr: ; SI = address of string to display LODSB OR AL,AL JZ SHORT putstrd MOV AH,0x0E MOV BX,0x0007 INT 0x10 ; print character to CRT JMP putstr putstrd: RETN ; return to caller bootfail: ; display failure message MOV SI,bootbad ; display error message CALL putstr XOR AX,AX ; wait for keypress INT 0x16 JMP 0xFFFF:0000 ; reboot machine readsect: ; ES:BX = Location ; AX = Sector MOV SI,[bsTrackSect] DIV SI ; divide logical sect by track size INC DL ; sector # begins at 1 MOV [bsReserv],DL ; sector to read XOR DX,DX ; logical track left in ax DIV WORD [bsHeadCnt] ; leaves head in dl, cyl in ax MOV DH, [bsBootDrv] ; XCHG DL,DH ; head to dh, drive to dl MOV CX,AX ; cyl to cx XCHG CL,CH ; low 8 bits of cyl to ch, hi 2 bits SHL CL,6 ; shifted to bits 6 and 7 OR CL, BYTE [bsReserv] ; or with sector number MOV AL,1 ; number of sectors MOV AH,2 ; use read function of int 0x13 PUSH DS INT 0x13 ; read sector POP DS JC bootfail ; display error message RET ; return to caller ; +-------------------------------------------------------------+ ; | Some more data used within boot.asm bootstrap file | ; +-------------------------------------------------------------+ padding TIMES 39 DB 0 bootmsg DB 'BOOT: ',0 bootgood DB 'GOOD',13,10,0 bootbad DB 'BAD',13,10,0 FileName DB 'SYSTEM SYS' BootSig DB 0x55, 0xAA