Underground

home *** CD-ROM | disk | FTP | other *** search

/ Underground / Underground CD1.iso / virii / zrodla / c / cache.asm < prev next >

Wrap

Assembly Source File | 1998-01-14 | 15.1 KB | 255 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 100H ;ORG = 100H to make this into a .COM file FIRST: JMP LOAD_CACHE ;First time through jump to initialize routine CPY_RGT DB '(C)1985 S.Holzner' ;A signature in bytes TBL_LEN DW 64 ;<-- # OF SECTORS TO STORE IN CACHE, MIN=24, MAX=124. ;THIS IS THE ONLY PLACE YOU MUST SET THIS NUMBER. EACH SECTOR = 512 BYTES. 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 DISK_CACHE PROC FAR ;The Disk interrupt will now come here. ASSUME CS:CODE_SEG CMP AX,201H ;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_MATCH ;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_MATCH ;get it. Or do we have it already? JCXZ NO_MATCH ;No, jump to No_Match, store sector MOV CX,512 ;ES:DI and DS:SI already set up from Find_Match 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,301H ;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 we don't want to 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_MATCH ; 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_Match, Xchg'd into DI MOV CX,512 ;Get ready to move 512 bytes REP MOVSB ;Here we go LEAVE: POP AX ;Here is the 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_Match CALL FIND_MATCH ;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_MATCH PROC NEAR ;This routine finds a sector in the sector bank PUSH AX ;And returns SI set to sector's entry, BX set LEA SI,SECTORS ; to the beginning of the 'table' -- the 3 words LEA BX,TABLE ;that precede all sectors. If there was no match MOV AX,TBL_LEN ; CX=0. 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_MATCH 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,SECTORS ;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,SECTORS ; 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: 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 File Alloc. Table 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 TABLE: DW 3 DUP(0) ;Table and sector storage begins right here SECTORS: ;First thing to write over is the following ; booster program. LOAD_CACHE PROC NEAR ;This procedure intializes everything LEA BX,CLEAR ASSUME DS:INTERRUPTS ;The data segment will be the Interrupt area MOV AX,INTERRUPTS MOV DS,AX MOV AX,word ptr DISK_INT ;Get the old interrupt service routine MOV word ptr INT13H,AX ; address and put it into our location MOV AX,word ptr DISK_INT[2] ; INT13H so we can call it. MOV word ptr INT13H[2],AX MOV word ptr DISK_INT,OFFSET DISK_CACHE ;Now load address of Cache MOV word ptr DISK_INT[2],CS ;routine into the Disk interrupt 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) MOV CX,AX ;Also, zero all the bytes so that ZERO: MOV BYTE PTR CS:[BX],0 ; Store_Sector will find 1st word a 0, INC BX ; indicating virgin territory. LOOP ZERO 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 LOAD_CACHE ENDP CLEAR: CODE_SEG ENDS END FIRST ;END "FIRST" so 8088 will go to FIRST first.