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Assembly Source File | 1986-01-24 | 25.4 KB | 555 lines

INTERRUPTS SEGMENT AT 0H ;This is where the disk interrupt ORG 13H*4 ;holds the address of its service routine DISK_INT LABEL DWORD INTERRUPTS ENDS CODE_SEG SEGMENT ASSUME CS:CODE_SEG org 2h pspsize dw ;size of physical machine org 80h parml db 0 org 81h parm db 127 dup (' ') ORG 100H ;ORG = 100H this is a .COM file FIRST: JMP load_pgm ;jump to initialize routine CPY_RGT DB '(C)85S.Holzner' ;A signature in bytes TBL_LEN DW 40h ;<-- # OF SECTORS IN CACHE, MIN=24, MAX=124. entries dw 0 ;used to count calls matches dw 0 ;count hits highwater dw 0 ;number of sectors in cache used TIME DW 0 ;Time used to time-stamp each sector OLD_CX DW 0 ;Stores original value of CX (CX is used often) LOW_TIM DW 0 ;Used in searching for least recently used sect. INT13H DD 0 ;Stores the original INT 13H address RET_ADR LABEL DWORD ;Playing games with the stack here to preserve RET_ADR_WORD DW 2 DUP(0) ;flags returned by Int 13H drive db 0ffh ;specific crive to be cached, if any 1,2,3,4... DISK_CACHE PROC FAR ;The Disk interrupt will now come here. ASSUME CS:CODE_SEG cmp drive,0ffh ;specific disk to be cached? je diskany ;if not, just go on cmp dl,drive ;if so, is this the right one? jne old_int ;if not, just return diskany: inc entries ;count entries into program CMP AX,0201H ;Is this a read (AH=2) of 1 sector (AL=1)? JE READ ;Yes, jump to Read CMP AH,3 ;No. Perchance a write or format? JB OLD_INT ;No, release control to old disk Int. JMP WRITE ;Yes, jump to Write OLD_INT:PUSHF ;Pushf for Int 13H's final Iret CALL INT13H ;Call the Disk Int JMP PAST ;And jump past all usual Pops READ: PUSH BX ;Push just about every register ever heard of PUSH CX PUSH DX PUSH DI PUSH SI PUSH DS PUSH ES MOV DI,BX ;Int 13H gets data address as ES:BX, switch to ES:DI ASSUME DS:CODE_SEG ;Make sure all labels found correctly PUSH CS ;Move CS into DS by pushing CS, popping DS POP DS MOV OLD_CX,CX ;Save original CX since we're about to use it CMP DH,0 ;DH holds requested head -- head 0? JNE NOT_FAT1 ;Nope, this can't be the first Fat sector CMP CX,6 ;If this is the directory, check if we have a JE FAT1 ; new disk. CMP CX,2 ;Track 0 (CH)? Sector 2 (CL)? JNE NOT_FAT1 ;If not, this sure isn't the FAT1 FAT1: CALL Find_sector ;DOS reads in this sector first to ; check disk format JCXZ NONE ;We'll use it for a check-sum. Do we have it MOV BX,DI ; stored yet? CX=0-->no. If yes, restore BX MOV CX,OLD_CX ; and CX from original values PUSHF ;And now do the Pushf and call of Int13H to read CALL INT13H ; FAT1 JC ERR ;If error, leave MOV CX,256 ;No error, FAT1 was read, check our value REPE CMPSW ; with CMPSW -- if no match, disk was changed JCXZ BYE ;Everything checks out, Bingo, exit. LEA SI,TABLE ;New Disk! Zero all the old disk's sectors MOV CX,TBL_LEN ;Loop over all entries, DL holds drive # CLR: CMP DS:[SI+2],DL ;Is this stored sector from the old disk? JNE NO_CLR ;Nope, don't clear this entry MOV WORD PTR DS:[SI],0 ;Match, zero this entry, zero first word NO_CLR: ADD SI,518 ;Move on to next stored sector (512 bytes of stored LOOP CLR ; sector and 3 words of identification & time-stamp) JMP BYE ;Reset for new disk, let's leave NONE: CALL STORE_SECTOR ;Store FAT1 if there was no match to it JC ERR ;Error -- exit ungraciously JMP BYE ;No Error, Bye. NOT_FAT1: ;The requested sector was not FAT1. Let's CALL Find_sector ;get it. Or do we have it already? JCXZ NO_MATCH ;No, jump to No_Match, store sector inc matches MOV CX,512 ;ES:DI and DS:SI already set up from Find_sector REP MOVSB ;Move 512 bytes to requested memory area CMP WORD PTR [BX+4],0FFFFH ;Is this a a directory sector? JE BYE ;Yes, don't reset time (already highest poss.) INC TIME ;No, reset the time, this sector just accessed MOV AX,TIME ;Move time into Time word of sector's 3 words MOV [BX+4],AX ; of identification JMP BYE ;And leave. If there's an article you'd like to NO_MATCH: ;see, by all means write in C/O PC Magazine. CALL STORE_SECTOR ;Don't have this sector yet, get it. JC ERR ;If read failed, exit with error BYE: CLC ;The exit point. Clear carry flag, set AX=1 MOV AX,1 ; CY=0 --> no error, AH=0 --> error code = 0 ERR: POP ES ;If error, preserve flags and AX with error code POP DS ;Pop all conceivable registers (except AX) POP SI POP DI POP DX POP CX ;Now that the flags are set, we want to get the POP BX ;old flags off the stack (put there by original PAST: POP CS:RET_ADR_WORD ;Int call) To do that we save the return address POP CS:RET_ADR_WORD[2] ;first and then pop the flags harmlessly POP CS:OLD_CX ;into Old_CX, and then jump to RET_ADR. JMP CS:RET_ADR ;Done with read. Now let's consider write. WRITE: PUSH BX ;Push all registers, past and present PUSH CX PUSH DX PUSH DI PUSH SI PUSH DS PUSH ES PUSH AX CMP AX,0301H ;Is this a write of one sector? JNE NOSAVE ;No, don't save it in the sector bank PUSH CS ;Yep, set DS (for call to Int13H label) and POP DS ; write this sector out PUSHF CALL INT13H JNC SAVE ;If there was an error don't save sector POP CS:OLD_CX ;Save AH error code, Pop old AX into Old_CX JMP ERR ;And jump to an ignoble exit SAVE: MOV OLD_CX,CX ;We're going to save this sector. MOV DI,BX ;Set up DI for string move (to store written CALL Find_sector ; sector. Do we have it in memory? (set SI) JCXZ LEAVE ;Nope, Leave (like above's Bye). XCHG DI,SI ;Exchange destination and source PUSH ES ;Set up DS:SI to point to where data written POP DS ; from. We'll then use a string move PUSH CS ;Set up ES so ES:DI points to sector bank POP ES ; SI was set by Find_sector, Xchg'd into DI MOV CX,512 ;Get ready to move 512 bytes REP MOVSB ;Here we go LEAVE: POP AX ;Here we leave JMP BYE ;Which only pops AX and then jumps to Bye NOSAVE: PUSH CS ;More than 1 sector written, don't save but POP DS ; do zero stored sectors that will be written MOV AH,0 ;Use AX as loop index (AL=# of sectors to write) TOP: PUSH CX ;Save CX since destroyed by Find_sector CALL Find_sector ;Do we have this one? JCXZ NOPE ;Nope if CX = 0 MOV WORD PTR [BX],0 ;There is a match, zero this sector NOPE: POP CX ;Restore CX, the sector index INC CL ;Move on to next one DEC AX ;Decrement loop index JNZ TOP ;And, unless that gives 0, go back again POPS: POP AX ;Pop 'em all, starting with AX POP ES POP DS POP SI POP DI POP DX POP CX POP BX JMP OLD_INT ;And go back to OLD_INT for write. DISK_CACHE ENDP Find_sector PROC NEAR ;This routine finds a sector in the sector bank PUSH AX ;And returns SI set to sector's entry, BX set ;to the beginning of the 'table' entry. ;If there was no match, CX = 0 LEA SI,SECTOR_data LEA BX,TABLE MOV AX,TBL_LEN ; When Int13H called, CH=trk #, CL=sec. # XCHG AX,CX ; DH=head #, DL=Drive #. Get Tbl_Len into CX FIND: CMP DS:[BX],AX ;Compare stored sector's original AX to current JNE NO ;If not, not. CMP DS:[BX+2],DX ;If so, check DX of stored sector with current JE GOT_IT ;Yes, there is a match, leave NO: ADD BX,518 ;Point to next Table entry ADD SI,518 ;And next sector too LOOP FIND ;Keep looping until there is a match GOT_IT: POP AX ;If there is no match, CX will be left 0 RET ;Return Find_sector ENDP STORE_SECTOR PROC NEAR ;This routine, as it says, stores sectors MOV BX,DI ;Original BX (ES:BX was original data address) MOV CX,OLD_CX ; and CX restored (CX=trk#, Sector#) PUSHF ;Pushf for Int 13H's Iret and call it CALL INT13H JNC ALL_OK ;If there was an exit, exit ignominiously JMP FIN ;If error, leave CY flag set, code in AH, exit ALL_OK: PUSH CX ;No error, push used registers PUSH BX ; and find space for sector in sector bank PUSH DX lea DI,SECTOR_data ;Point to sector bank LEA BX,TABLE ; and Table MOV CX,TBL_LEN ; and get ready to loop over all of them to CHK0: CMP WORD PTR DS:[BX],0 ;find if there is an unused sector JE FOUND ;If the first word is 0, use this sector ADD DI,518 ;But this one isn't so update DI, SI and ADD BX,518 ; loop again LOOP CHK0 MOV LOW_TIM,0FFFEH ;All sectors were filled, find least recently LEA DI,SECTOR_data ; used and write over that one LEA SI,TABLE MOV CX,TBL_LEN ;Loop over all stored sectors CHKTIM: MOV DX,LOW_TIM ;Compare stored sector to so-far low time CMP [SI+4],DX JA MORE_RECENT ;If this one is more recent, don't use it MOV AX,DI ;This one is older than previous oldest MOV BX,SI ;Store sector bank address (DI) and table MOV DX,[SI+4] ; entry (now in SI) MOV LOW_TIM,DX ;And update the Low Time to this one MORE_RECENT: ADD DI,518 ;Move on to next stored sector ADD SI,518 ;And next table entry LOOP CHKTIM ;Loop again until all covered MOV DI,AX ;Get Sector bank address of oldest into DI FOUND: mov highwater,cx ;remember how much we searched POP DX ;Restore used registers POP SI ;Old BX (data read-to-address) --> SI POP CX MOV [BX],CX ;Store the new CX as the sector's first word MOV [BX+2],DX ;2nd word of Table is sector's DX INC TIME ;Now find the new time MOV AX,TIME ;Prepare to move it into 3rd word of Table CMP DH,0 ;Is this directory or FAT? (time-->FFFF) JNE SIDE1 ;If head is not 0, check other head CMP CX,9 ;Head zero, trk# 0, first sector? (directory) JLE DIR ;Yes, this is a piece we always want stored JMP NOT_DIR ;No, definitely not FAT or directory SIDE1: CMP DH,1 ;Head 1? JNE NOT_DIR ;No, this is not FAT or directory CMP CX,2 ;Part of the top of the directory? JA NOT_DIR ;No, go to Not_Dir and set time DIR: MOV AX,0FFFFH ;Dir or FAT, set time high so always kept NOT_DIR:MOV [BX+4],AX ;Not FAT or dir, store the incremented time PUSH ES ;And now get the data to fill the sector POP DS ;SI, DI already set. Now set ES and DS for PUSH CS ; string move. POP ES MOV CX,512 ;Move 512 bytes REP MOVSB ;Right here CLC ;Clear the carry flag (no error) FIN: RET ;Error exit here (do not reset CY flag) STORE_SECTOR ENDP ;When Int13H called, CH=trk # CL=sector # ; DH=head # (0,1) DL=Drive # (0,1,2,3) ; AH=operation AL=number of sectors ; ES:BX=I/O buffer address ; Operations are: 2=Read Sector(s) 3=Write Sectors ; 4=Verify Sectors 5=Format track ;Format Buffer Contains 4 byte commands as reqd for 1 track ; Byte 1 = Track Number Byte 2 = Head Number ; Byte 3 = Sector Number Byte 4 = Bytes/Sector Code ;Bytes/Sector code is: 00=128 01=256, 02=512 03=1024 ;Carry flag is 0 if operation successful, 1 for error ;AL = Number of bytes actually processed for Read/Write/Verify ;Table entry layout is: ;1st word of table entry: sector's CX (track number and sector number) ;2nd word of Table entry: sector's DX (head number and drive number) ;3rd word is the incremented "time" ; unless sector is FAT or DIR, in which case it is FFFFh ;Remaining 256 words are 512 bytes of the sector's contents. zero proc near pop ax ;fix up the stack (offset) ; pop ax ;fix up the stack (CS) pop ax ;get back program length mov cx,ax ;Also, zero all the bytes shr cx,1 ;divide iterations by 2 push cs pop es ;set up es mov si,offset table mov di,offset sector_data repe movsw ;zero the world MOV DX,OFFSET TABLE ;To attach in memory, add # bytes to ADD DX,AX ; store to Table's location and use INT 27H ; Int 27H exit and make resident zero endp TABLE: DW 3 DUP(0) ;Table and sector storage begins right here Sector_data: ;First thing to write over is the following ; booster program. cr equ 13 lf equ 10 parmptr dw 81h ;address of 'current' byte in parms radix dw 10 ;radix for conversions drivemsg db cr,lf,'Disk ' drivewhere db ' ',' cache:' db cr,lf,'$' driveerrmsg db cr,lf,'Disk err - use A-D',cr,lf,'$' sizeerrmsg db cr,lf,'Size err - use 24-124',cr,lf,'$' sizemsg db cr,lf sizedec db 6 dup(' '),' bytes at ' lochex db 4 dup(' '),':0 ' remdec db 6 dup(' '),' free' db cr,lf,cr,lf,'$' asciitable db '0123456789ABCDEF' ;table of characters asciibin proc near ;si - source of characters (left end) ;ax - contents in binary ;cx - length in bytes xor ax,ax xor bx,bx asciiloop: mov bl,[si] ;get character pointed to by SI cmp bl,' ' ;is character a blank? je asciiexit ;if so, that is it. cmp bl,'0' jl asciierror mul radix ;multiply ax by radix cmp bl,'9' jg asciihex ;if character > 9 must be hex and bl,0fh ;pick up numeric part asciiadd: ;add to accumulator add ax,bx inc si ;scan right loop asciiloop cmp bl,bl ;set zero flag jmp asciiret asciihex: cmp radix,10 ;radix >10? jle asciierror ;if not, error or bl,20h ;make lower case cmp bl,'a' jl asciierror cmp bl,'f' jg asciierror sub bl,87 ;turn 'A' into 10, etc jmp asciiadd asciierror: xor ax,ax ;return a zero on error asciiexit: cmp bl," " ;set zero flag = no error asciiret: mov parmptr,si ;remember where we are at mov parml,cl ;remember our length ret asciibin endp binascii proc near ;di - target of characters (left just) ;dx - most significant bits ;ax - least significant bits ;storage - radix mov si,offset asciitable xor bh,bh ;clear bh xchg bp,dx ;ax,dx contain data binloop: xchg ax,bp ;get high word (dx) xor dx,dx ;clear result div radix ;divide ax by radix xchg bp,ax ;get low word (ax) div radix ;divide mov bl,dl ;get into a register mov dl,cs:[bx+si] ;get right ascii character mov [di],dl ;and drop at target dec di ;set up for next character cmp ax,0 ;make sure something's left jnz binloop ;if there is more loop ret binascii endp lineout proc near ;proc to type out a line mov byte ptr [di],cr ;move in carriage return inc di mov byte ptr [di],lf ;move in line feed inc di mov byte ptr [di],'$' ;move in stopper mov ah,9h ;do screen i/o int 21h ret lineout endp scanparm proc near ;get start of next parm in SI xor cx,cx mov al,' ' ;put blank in accumulator mov si,parmptr ;get offset of parameter mov cl,parml ;get length of remaining parm cmp cl,0 ;is there any parm left? je scanret ;if not, just exit scanloop: lodsb ;get byte pointed to by SI cmp al,' ' ;is it blank? jne scangot loop scanloop ;if so, loop on jmp scanset scangot: dec si ;back up over character scanset: mov parmptr,si ;remember where we are at mov parml,cl ;remember our length scanret: cmp al,' ' ;set zero flag ret scanparm endp Load_pgm PROC NEAR ;This procedure intializes everything call scanparm ;call scan for start of parm je noparm ;if none, skip checking parms call asciibin ;turn chars into binary in ax mov dx,offset sizeerrmsg jnz parmerr ;if errors, skip out mov tbl_len,24 ;set minimum size cmp ax,24 ;smaller than minimum? jl parmerr ;if so, complain cmp ax,124 ;larger than max? jng loadsize ;if not, do what he asks mov tbl_len,124 ;if error then set max jmp parmerr ;and complain loadsize: mov tbl_len,ax call scanparm ;call scan for start of parm je noparm ;if none, skip checking parms and al,255-20h ;make upper case mov drivewhere,al;store in message mov dx,offset driveerrmsg or al,20h ;make lower case cmp al,'a' ;drive must be a to d jl parmerr cmp al,'d' jg parmerr ;if not, will ignore sub al,'a' ;make a = 0, b = 1, etc mov drive,al mov dx,offset drivemsg parmerr: mov ah,9 ;dos function: type string int 21h noparm: ASSUME DS:INTERRUPTS ;The data segment will be the Interrupt area MOV AX,INTERRUPTS MOV DS,AX MOV AX,DISK_INT ;Get the old interrupt service routine MOV INT13H,AX ; address and put it into our location MOV AX,DISK_INT[2] ; INT13H so we can call it. MOV INT13H[2],AX MOV DISK_INT,OFFSET DISK_CACHE ;Now load the address of Cache MOV DISK_INT[2],CS ;routine into the Disk interrupt push cs ;back to normal addressibility pop ds assume ds:code_seg ;Make sure all labels found correctly MOV AX,TBL_LEN ;The number of sectors to store in cache MOV CX,518 ;Multiply by 518 (3 words of id and 512 MUL CX ; bytes of sector data) in AX push ax ;save ax xor dx,dx ;clear hi bytes mov di,offset sizedec+5 ;set target call binascii push cs ;cs - where we are loaded pop ax ;get it into ax for conversion mov radix,16 ;housekeeping xor dx,dx ;clear hi bytes mov di,offset lochex+3 ;set target call binascii push cs ;cs - where we are loaded pop bx ;get it into bx for subtraction mov ax,pspsize ;size of machine 5000h = 320k sub ax,bx ;knock off where we are at mov dx,ax ;get high bytes in accum ext mov cl,12 shr dx,cl ;orient correctly mov cl,4 shl ax,cl ;shift bytes in accum pop bx ;get our length off stack push bx sub ax,bx ;deduct length of this pgm sbb dx,0 ;if borrow, count it mov radix,10 ;now base 10 mov di,offset remdec+5 ;set target call binascii mov dx,offset sizemsg mov ah,9 ;dos function: type string int 21h call zero ;finish up Load_pgm ENDP CODE_SEG ENDS END FIRST ;END 8088 will go to FIRST first.