гEOпAINT фILE фORMAT -------------------- BY бRUCE жRIELING (BVRIELING@UNDERGRAD.MATH.WATERLOO.EDU) гEOпAINT IS AN EXCELLENT GRAPHICS PROGRAM WRITTEN FOR THE геос ENVIRONMENT. иTS DISK ACCESS IS RELATIVELY QUICK, COMPARED IT TO WHAT A COMPARABLE PROGRAM WOULD DO ON A NON-геос EQUIPPED ц64. пART OF THIS ACCOMPLISHMENT CAN BE ATTRIBUTED TO THE DISKтURBO THAT IS AN INTEGRAL PART OF геос. хOWEVER, THE SPECIAL гEOпAINT FILE-SAVING SCHEME DESERVES SOME OF THE CREDIT. жлир ---- гEOпAINT FILES ARE ALWAYS STORED IN жARIABLE лENGTH иNDEXED рECORDING FILES. жлир FILES OFFER ADVANTAGES NOT AVAILABLE WITHOUT геос. гENERALLY SPEAKING, жлир IS THE ULTIMATE IN релатиже FILES. тHE FORMAT OF A жлир FILE IS NOT THAT DIFFICULT TO FIGURE OUT. вHILE IN A REGULAR ц64 FILE, THE TWO BYTES DIRECTLY FOLLOWING THE филетыпе BYTE IN THE DIRECTORY WOULD POINT TO THE DATA FILE FOLLOWING, жлир FILES USE THESE TWO BYTES TO POINT TO A жлир хеадер блоцк (DON'T CONFUSE THE жлир хеадер BLOCK WITH THE инфо BLOCK). тHE FIRST TWO BYTES OF THIS BLOCK ARE $00/фф, AS THE HEADER BLOCK IS A маьимум OF ONE BLOCK LONG. (тHIS IS WHY WHEN YOU жалидате A геос DISK FROM ц64 MODE, гEOпAINT PICTURES ARE LOST. оNLY THE HEADER BLOCK IS RECOGNISED AS BEING PART OF THE FILE. тHE REST OF THE PICTURE GETS DEALLOCATED IN THE бам). тHE REMAINING 254 BYTES IN THE BLOCK ARE DIVIDED INTO 127 2-BYTE POINTERS TO TRACKS/SECTORS ON THE DISK. тHESE POINTERS POINT TO THE INDIVIDUAL RECORDS OF THE жлир FILE, WHICH MAY BE аны NUMBER OF BLOCKS LONG. тHE жлир TRACK/SECTOR POINTERS IN THE жлир HEADER BLOCK ONLY POINT TO THE фирст BLOCK OF THE CHAIN. фROM THEN ON, THE SECTORS CHAIN THEMSELVES TOGETHER USING THE NORMAL FORMAT IE. THE FIRST TWO BYTES OF EACH BLOCK POINT TO THE FOLLOWING BLOCK. а SAMPLE гEOпAINT жлир HEADER MIGHT LOOK LIKE THIS: 0000:00 фф 03 11 03 05 03 01 ........ 0008:04 03 00 фф 00 фф 00 фф ........ 0010:04 07 00 00 00 00 00 00 ........ ETC.... тHE FIRST TWO BYTES, $00/фф, TELL THE DRIVE THAT THIS IS THE LAST (AND ONLY) BLOCK IN THIS жлир хеадер сецтион (WILL NEVER BE MORE THAN 1 BLOCK, AS WAS MENTIONED EARLIER). тHE NEXT PAIR OF BYTES, $03/11, POINTS TO THE FIRST жлир RECORD. тHE NEXT TWO, $03/05, POINT TO THE SECOND RECORD. ыOU WILL NOTICE THAT 5TH RECORD CONTAINS THE VALUES $00/фф. тHIS MEANS THAT FOR THIS RECORD, THERE IS NO PICTURE DATA. вE WILL GET INTO EXACTLY WHAT THE DATA HELD IN THE RECORDS MEAN IN A MINUTE. тHE $00/фф ENTRIES INDICATE AN EMPTY RECORD. фINALLY, THE 9TH ENTRY, $00/00 INDICATES THE END OF THE гEOпAINT FILE. тHERE IS NO MORE DATA BEYOND THIS POINT. оNE NOTE SHOULD BE MADE. гEOпAINT IS NOT ALWAYS CONSISTENT IN ITS HANDLING OF THE DATA IN A HEADER BLOCK. сOMETIMES, IT WILL SHOW QUITE A FEW $00/фф COMBINATIONS BEFORE FINALLY TERMINATING WITH A $00/00. вHEN READING THE FILE, и ALWAYS READ THE ENTIRE HEADER, AS и DON'T TRUST THE END OF FILE METHOD MENTIONED ABOVE. йUST REMEMBER THAT ANY TRACK/SECTOR LINK THAT DOES NOT CONTAIN $00/фф OR $00/00 IS A VALID RECORD, WITH PICTURE DATA. лAYOUT ON сCREEN ---------------- геос ORIENTS THE DATA IN A гEOпAINT FILE SLIGHTLY DIFFERENTLY THAN IN A пHOTOсCRAP OR AN иCON. а PHOTOSCRAP STORES THE BYTES CORROSPONDING TO A SCREEN WHICH LOOKS LIKE THIS: 001 002 003 004 005 ....0012 013 014 015 016 017 ....0024 цONSECUTIVE BYTES ARE PLACED бесиде EACH OTHER. хOWEVER, IF YOU ARE AT ALL FAMILIAR WITH THE LAYOUT OF A ц64 HI-RES SCREEN, YOU WILL KNOW THIS IS VERY DIFFERENT FROM THE LAYOUT THAT THE жиц CHIP SEES DATA. гEOпAINT USES A FORMAT IDENTICAL TO THE жиц CHIP LAYOUT ON SCREEN. гEOпAINT PICTURES ARE STORED IN THE FOLLOWING FORMAT: 001 009 017 025 033 ..... 313 002 010 018 026 034 ..... 314 003 011 019 027 035 ..... 315 004 012 020 028 036 ..... 316 005 013 021 029 037 ..... 317 006 014 022 030 038 ..... 318 007 015 023 031 039 ..... 319 008 016 024 032 040 ..... 320 321 329 ..... 322 330 ..... 323 331 ..... 324 332 ..... 325 333 ..... 326 334 ..... 327 335 ..... 328 336 ..... аS YOU CAN SEE, THIS IS VERY DIFFERENT FROM THE пHOTOсCRAP FORMAT. цONSECUTIVE BYTES ARE нот STORED ON THE SCREEN BESIDE EACH OTHER. рATHER, THEY ARE STORED UNDERNEATH EACH OTHER INTO GROUPS OF 8 BYTES. тHIS MAKES MOVING THE DATA FROM THE DISK ONTO THE SCREEN THAT MUCH FASTER, AS THE DECOMPACTED BYTES CAN JUST BE STORED ON THE SCREEN AFTER EACH OTHER. оF COURSE, THIS MAKES PORTING геос PICS TO THE 128'S ждц THAT MUCH MORE DIFFICULT, AS THE ждц CONFORMS TO THE пHOTOсCRAP FORMAT. цOMPRESSION мETHOD ------------------ геос USES AN EXCELLENT COMPRESSION METHOD TO STORE FILES ON DISK. ыOU MAY HAVE NOTICED THAT NEARLY EMPTY PICTURES ON DISK CONSUME VERY LITTLE DISK SPACE. тHIS CAN BE CREDITED TO гEOпAINT'S SMART COMPRESSION TECHNIQUES. бASICALLY, THE FORMAT OF THE COMPRESSION HAS ONE цомманд BYTE FOLLOWED BY ONE OR MORE дата BYTES. тHE цомманд BYTE TELLS геос WHAT TO DO WITH FOLLOWING дата BYTES. тHERE ARE 4 COMMANDS FOR COMPRESSION: 1) иF THE цомманд BYTE IS LESS THAN 64, THIS INDICATES THAT THERE ARE 'цомманд' MANY дата BYTES FOLLOWING THAT ARE TO BE TAKEN AS INDIVIDUAL BYTES. тHIS IS THE LEAST EFFECTIVE METHOD OF COMPRESSION, AS NO COMPRESSION TAKES PLACE. 2) иF THE цомманд BYTE RANGES FROM 65 TO 127, THEN THIS IS A SPECIAL TYPE OF COMPRESSION. фIRST OF ALL, THE NEXT 8 BYTES IN THE FILE ARE READ IN AS дата. тHIS дата IS USED TO MAKE AN 8*8 'STAMP'. сECONDLY, THE AMOUNT OF TIMES TO 'STAMP' THIS 8*8 SQUARE IS CALCULATED (цомманд анд 63). тHEN, THE STAMPING IS DONE. 'сTAMPING' SOUNDS MORE DIFFICULT THAT IT REALLY IS. вHAT IT BOILS DOWN TO, IS REPEATING THE 8 BYTE дата STAMP 'цомманд анд 63' TIMES. 3) иF THE цомманд BYTE IS 129 OR GREATER, THEN THE FOLLOWING дата BYTE IS REPEATED 'цомманд анд 127' TIMES. тHIS IS DIFFERENT FROM #1, AS ONLY 1 дата BYTE IS CALLED IN, AND SIMPLY REPEATED. #1 CALLED IN 'цомманд' MANY дата BYTES. 4) иF THE цомманд BYTE IS зеро, WE HAVE REACHED THE END OF THE жлир RECORD FOR THE гEOпAINT PICTURE. иT SHOULD BE NOTED THAT THE цомманд BYTE WILL нежер BE 64 OR 128. иF IT IS, THERE HAS BEEN AN ERROR. фORMAT OF дATA аFTER дECOMPACTING --------------------------------- аFTER THE DATA HAS BEEN DECOMPACTED, IT REMAINS TO BE PLACED ON THE SCREEN. еACH жлир RECORD HOLDS 16 SCANLINES OF DATA, OR 2 CHARACTER LINES (DIFFERENT WAYS OF LOOKING AT THE SAME THING). тHE FORMAT OF THE DATA IS AS FOLLOWS: фIRST, THERE IS 640 BYTES OF PICTURE DATA, COMPRISING THE FIRST CHARACTER LINE (8 SCANLINES). рEMEMBER, гEOпAINT PICTURES ARE 640 PIXELS ACROSS. 640 PIXELS WORKS OUT TO 80 BYTES. а CHARACTER LINE IS 8 PIXELS DEEP, SO 80*8 COMES TO 640 BYTES. тHESE BYTES ARE FOLLOWED BY THE 640 BYTES FOR THE SECOND CHACACTER LINE (NEXT 8 SCANLINES). тHIS IS FOLLOWED BY 8 GARBAGE BYTES THAT ACCIDENTALY WORKED THEMSELVES INTO THE ORIGINAL гEOпAINT DESIGN. тHEY SHOULD BE SET TO ZERO. фINALLY, TWO SETS OF 80 BYTES OF COLOUR DATA FOLLOW. тHE FIRST SET COMPRISES THE COLOUR FOR THE FIRST LINE, THE SECOND 80 BYTES FOR THE SECOND LINE. тO WRAP THINGS UP, THE жлир RECORD IS TERMINATED BY A ZERO BYTE. тHE NEXT жлир RECORD WILL HOLD THE DATA FOR THE неьт 16 SCANLINES, AND SO ON. цONCLUSION ---------- тHAT ABOUT WRAPS UP THIS DISCUSSION ON гEOпAINT FORMAT FOR FILES. вE'VE DISCUSSED THE FORMAT OF жлир FILES ON DISK, LAYOUT OF PICTURE DATA ON SCREEN, COMPRESSION METHODS USED IN гEOпAINT FILES, AND THE FORMAT OF THE DATA ONCE DECOMPACTED. и HOPE THIS INFORMATION WILL COME IN HANDY FOR SOMEONE. ============================================================================== рASTERS - вHAT тHEY аRE AND хOW TO уSE тHEM BY бRUCE жRIELING - (BVRIELING@UNDERGRAD.MATH.WATERLOO.EDU) аNYONE WHO HAS FIDDLED AROUND WITH INTERRUPTS ON THE цOMMODORE 64 HAS UNDOUBTEDLY HEARD AT ONE TIME OR ANOTHER OF THE CONCEPT OF RASTERS BEING MENTIONED. рASTERS ARE THE 'ULTIMATE' ACHIEVEMENT OF INTERRUPT PROGRAMMING, OR SO THEY SAY. вHAT IS A RASTER? аND HOW DOES ONE GO ABOUT WRITING A PROGRAM TO USE THEM? оVERVIEW OF WHAT иNTERRUPTS ARE ALL ABOUT ----------------------------------------- а RASTER IS SORT FORM FOR THE CONCEPT OF A 'RASTER INTERRUPT'. бEFORE GOING INTO RASTERS, PERHAPS A BRIEF REVIEW OF INTERRUPTS IS IN ORDER. иNTERRUPTS ARE EVENTS GENERATED BY THE циа TIMER IN THE ц64 TO PERFORM CERTAIN TASKS. 60 TIMES A SECOND, THE циа CHIP SIGNALS AN INTERRUPT IS DUE TO BE PROCESSED (IE. THE INTERRUPT TIMER TIMED OUT). тHIS CAUSES THE 6510 цпу TO STOP EXECUTING THE CURRENT PROGRAM, SAVE THE REGISTERS ON THE STACK, AND BEGIN TO EXECUTE THE INTERRUPT CODE. сOME OF THE THINGS WHICH GET DONE DURING AN INTERRUPT INCLUDE THE KEYBOARD SCAN, AND UPDATING ти (THE SOFTWARE CLOCK). вHEN THE INTERRUPT CODE IS FINISHED, AN рти INSTRUCTION IS EXECUTED, WHICH BRINGS THE INTERRUPT'S EXECUTION TO A HALT. тHE REGISTERS ARE RETRIEVED FROM THE STACK, AND THE CURRENT PROGRAM IN MEMORY CONTINUES TO EXECUTE ONCE AGAIN. иT WILL CONTINUE TO DO SO UNTIL THE NEXT INTERRUPT OCCURS, ABOUT 1/60 OF A SECOND LATER. тHE ABOVE IS WHAT HAPPENS IN A NORMAL ц64 (THE ц128 FOLLOWS THE SAME IDEA, BUT MORE EVENTS OCCUR DURING A ц128 INTERRUPT). [еD. нOTE: иN ADDITION, THE ц=128 GENERATES ITS INTERRUPTS VIA A SCREEN RASTER INSTEAD OF THE циа CHIP.] хOWEVER, YOU CAN CHANGE THE NORMAL COURSE OF EVENTS, AND CAUSE SOME CODE OF YOUR DESIGN TO BE ADDED TO THE NORMAL LIST OF EVENTS WHICH OCCUR EVERY INTERRUPT. сOME OF THE SIMPLE FAVOURITES INCLUDE FLASHING THE BORDER 60 TIMES PER SECOND. (нOTE THAT WE HAVE NOT BEGUN THE TOPIC OF RASTERS YET; THIS HAS NOTHING TO DO WITH RASTERS. тHAT DISCUSSION BEGINS AT THE NEXT HEADING.) хOW DO YOU CHANGE THE INTERRUPT'S NORMAL COURSE OF ACTION? иT'S RATHER SIMPLE. тHE ц64 CONTAINS AN INTERRUPT жецтор AT LOCATIONS 788/9 WHICH IS 'JUMPED THROUGH' BEFORE THE кERNAL рOM GETS A CHANCE TO EXECUTE ITS CODE. иF YOU CHANGE THIS VECTOR TO POINT TO ыоур CODE, AND MAKE THE END OF YOUR CODE POINT TO THE NORMAL кERNAL LOCATION (WHERE THE INTERRUPT NORMALLY WOULD HAVE JUMPED TO, $еа31), AND YOU ARE CAREFUL NOT TO STEP ON ANYTHING, YOUR CODE WILL BE EXECUTED 60 TIMES PER SECOND. аN EXAMPLE IS IN ORDER: ; FLASHER ; ; THIS PROGRAM CAUSES THE BORDER TO FLASH 60 TIMES PER SECOND ; SETUP = * SEI ; DISABLE INTERRUPTS LDA #INTCODE ; DO THE SAME WITH THE HIGH BYTE STA 789 CLI ; RE-ENABLE INTERRUPTS RTS ; RETURN TO CALLER INTCODE = * INC $D020 ; CHANGE BORDER COLOUR JMP $EA31 ; EXIT BACK TO ROM тHE ABOVE IS AN EXAMPLE OF A VERY SIMPLE INTERRUPT ROUTINE. иF YOU WERE TO ASSEMBLE IT WITH AN ASSEMBLER, AND сыс TO THE сетуп ROUTINE, YOU WOULD SEE YOUR BORDER FLASH 60 TIMES PER SECOND. ыOU WILL NOTICE THE сеи AND цли MACHINE LANGUAGE INSTRUCTIONS USED ABOVE. тHEY ARE VERY IMPORTANT. вE DON'T WANT AN INTERRUPT OCCURRING IN BETWEEN THE ста 788 AND THE ста 789 INSTRUCTIONS. тHINK WHAT WOULD HAPPEN IF ONE DID: 788 WOULD HAVE BEEN MODIFIED, BUT 789 WOULD STILL BE POINTING TO THE HIGH BYTE OF THE кERNAL ADDRESS. рESULT: THE INTERRUPT WOULD HAVE JUMPED TO HEAVEN KNOWS WHERE. ыOU CAN BE VIRTUALLY GUARANTEED THAT IT WOULD нот BE POINTING TO A VALID PIECE OF INTERRUPT CODE. ыOUR MACHINE WOULD CRASH. тHE сеи INSTRUCTION TURNS INTERRUPTS офф, SO THAT THERE IS NO DANGER OF AN INTERRUPT OCCURRING DURING EXECUTION OF THE FOLLOWING ROUTINE. тHE цли TURNS THEM BACK ON. иF YOU FORGET TO TURN THEM BACK ON, AND ACCIDENTALLY LEAVE THEM OFF, YOUR KEYBOARD WILL FREEZE WHEN YOU RETURN TO BASIC, AND YOUR MACHINE WILL SEEM TO LOCK UP. тHE ABOVE WAS A VERY SIMPLE EXAMPLE. тHERE ARE MANY USEFUL THINGS WHICH CAN ALSO BE DONE ON AN INTERRUPT. и HAVE SEEN CODE WHICH PLAYED MUSIC IN THE BACKGROUND OF A RUNNING бASIC PROGRAM (IT PLAYED THE POPULAR .мус FILES). геос USES INTERRUPTS EXTENSIVELY TO CONTROL THE POINTING OF THE MOUSE, AND TO TRIGGER EVENTS. иNTERRUPTS ARE POWERFUL BEASTS, AND THE FOLLOWING CONCEPT CONCERNING RASTER INTERRUPTS SPECIFICALLY IS A PARTICULARLY USEFUL ANIMAL FOR SOME PEOPLE. тHE рASTER ---------- а RASTER IS A LOOSELY USED TERM. иT REFERS TO AN INTERRUPT THAT IS TRIGGERED WHEN THE RAY GUN ON THE BACK OF YOUR MONITOR DRAWS A CERTAIN LINE ON THE VIDEO SCREEN. тHERE ARE MANY DIFFERENT SOURCES WHICH CAN CAUSE AN INTERRUPT. ыOU ARE NOT LIMITED TO WHAT THE циа CHIP CAN DO. рASTERS DEPEND ON INTERRUPTS SPECIFICALLY GENERATED BY THE жидео CHIP. ыOU COULD MAKE THIS INTERRUPT CHANGE THE BORDER COLOUR OF THE SCREEN BELOW A CERTAIN SCREEN LINE. вHEN THE SCREEN LINE YOU SPECIFIED GETS REDRAWN, THE INTERRUPT GOES OFF. ыOUR CODE THEN QUICKLY CHANGES SOME MEMORY LOCATIONS TO CREATE A DIFFERENT VIDEO MODE OR EFFECT. ыOU COULD CAUSE THE BOTTOM HALF OF THE SCREEN TO GETS IT'S CHARACTER DEFINITIONS FROM ANOTHER, DIFFERENT CHARACTER SET. оR, YOU COULD MAKE THE TOP 3/4 OF YOUR SCREEN EXIST IN HI-RES MULTI-COLOUR GRAPHICS, AND KEEP THE BOTTOM 1/4 OF THE SCREEN IN TEXT MODE. сOME FACTS ABOUT THE VIDEO SCREEN: IT GETS REDRAWN EXACTLY 60 TIMES PER SECOND. иT CONTAINS 200 SCAN LINES ON THE NORMAL 25*40 DISPLAY, NUMBERED 50 TO 250 OR THEREABOUTS (NOTE THAT THERE ARE MORE VISIBLE SCAN LINES THOUGH: THE TOP AND BOTTOM BORDERS, FOR EXAMPLE). тHE ACTUAL RE-DRAWING OF THE SCREEN IS SYNCHRONIZED TO THE ELECTRICAL POWER COMING INTO YOUR HOUSE, 60 хZ. тHAT'S WHY SOME PROGRAMS BEHAVE DIFFERENTLY WHEN RUN ON еUROPEAN MACHINES. тHE POWER IS DELIVERED AT 50 хZ OVER THERE. вHY DO WE HAVE TO WORRY ABOUT A VIDEO INTERRUPT? иF THE SCREEN GETS REDRAWN 60 TIMES PER SECOND, AND REGULAR INTERRUPTS ALSO OCCUR AT 60 TIMES PER SECOND, WHY NOT SIMPLY PUT SOME CODE INTO THE REGULAR INTERRUPT TO DO WHAT WE WANT WITH THE SCREEN? бECAUSE THE TWO TYPES OF INTERRUPTS ARE NOT IN SYNC. нEITHER ONE OF THEM OCCURS еьацтлы 60 TIMES PER SECOND, AND THE DIFFERENCES ARE ENOUGH TO MAKE IT NEXT TO IMPOSSIBLE TO GET COORDINATED ACTIVITY OF ANY KIND HAPPENING ON THE SCREEN. вHEN WE USE THE VIDEO INTERRUPT, WE кнов WE ARE AT A CERTAIN LINE ON THE SCREEN, AS BEING ON THAT LINE IS WHAT CAUSED THE INTERRUPT TO HAPPEN IN THE FIRST PLACE. сO, LET'S SUMMARIZE. вE KNOW THAT REGULAR INTERRUPTS OCCUR 60 TIMES PER SECOND. вE ALSO KNOW THAT THE VIDEO SCREEN GETS RE-DRAWN 60 TIMES PER SECOND, AND THAT WE CAN CAUSE AN INTERRUPT TO BE GENERATED WHEN A CERTAIN LINE GETS DRAWN ON THE SCREEN. оNE SLIGHT DRAWBACK TO ALL OF THIS IS THAT ботх TYPES OF INTERRUPTS (REGULAR AND RASTER DRIVEN) TRAVEL THROUGH THE саме VECTOR (IE. ABOUT 120 INTERRUPTS PER SECOND, 60 OF ONE, AND 60 OF THE OTHER). ыOUR CODE WILL HAVE TO CHECK AND SEE WHAT THE SOURCE OF THE INTERRUPT WAS, AND ACT ACCORDINGLY. оR WILL IT? тHE SYSTEM NEEDS AN INTERRUPT TO OCCUR 60 TIMES PER SECOND TO DO HOUSEKEEPING, AND USES THE циа CLOCK TO GENERATE THE INTERRUPTS. вE WANT TO INTERRUPT EVERY TIME A CERTAIN SCAN LINE IS REACHED ON THE MONITOR, WHICH WILL ALSO JUST HAPPEN TO OCCUR AT 60 TIMES PER SECOND. вE ALSO HAVE TO MAKE SURE THAT THEY DON'T INTERFERE WITH EACH OTHER. тHE REGULAR INTERRUPTS SHOULD BE SENT TO THEIR рOM DESTINATION, WHILE OUR VIDEO INTERRUPTS SHOULD GO TO OUR CODE, AND NO WHERE ELSE. иF BOTH ARE OCCURRING AT 60 TIMES PER SECOND, WHY NOT DO THE JOB OF THE SYSTEM рOM, AND OUR VIDEO CODE ON THE саме INTERRUPT? вE KNOW THAT THE циа CHIP IS NOT GOOD FOR THIS; IT IS OUT OF SYNC WITH THE VIDEO IMAGE. вHY NOT TURN офф THE циа INTERRUPT, ENABLE THE RASTER/VIDEO INTERRUPT, AND DO BOTH JOBS ON ONE INTERRUPT? тHEN WE WOULD HAVE AN INTERRUPT SIGNAL THAT OCCURS 60 TIMES PER SECOND, AND IS IN PERFECT SYNC WITH THE VIDEO IMAGE. тHAT'S EXACTLY WHAT WE'RE GOING TO DO. аSTUTE READS WILL NOTICE A SLIGHT FLAW IN THE ABOVE LOGIC. фOR SIMPLIFICATION PURPOSES, и DIDN'T GET INTO THE FACT THAT YOU WILL NEED тво RASTER INTERRUPTS пер сцреен TO ACCOMPLISH ANYTHING USEFUL. вHY TWO? бECAUSE ANY CHANGE TO THE VIDEO MODE YOU PUT INTO EFFECT 3/4 OF THE WAY DOWN THE SCREEN WILL HAVE TO BE UNDONE AT THE топ OF THE NEXT SCREEN UPDATE. иF YOU DECIDE TO MAKE THE TOP 3/4 OF THE SCREEN A HI-RES IMAGE, AND THE BOTTOM 1/4 TEXT, YOU NEED ONE INTERRUPT 3/4 OF THE WAY DOWN THE SCREEN TO CHANGE FROM HI-RES TO TEXT, BUT YOU NEED A сецонд ONE AT THE TOP OF THE SCREEN TO CHANGE BACK TO HI-RES FROM TEXT. сO, WE WILL NOW HAVE 120 INTERRUPTS GOING OFF EVERY SECOND TO ACCOMPLISH OUR VIDEO DESIRES, WITH 60 OF THEM WORKING A DOUBLE SHIFT, MAKING SURE THE SYSTEM INTERRUPT CODE GETS EXECUTED ALSO. рEMEMBER THAT WE ARE WORKING WITH A SPECIFIC EXAMPLE. тHERE IS NO REASON WHY YOU COULDN'T SPLIT THE SCREEN INTO н DIFFERENT VIDEO MODES, AND HAVE (н+1)*60 INTERRUPTS GOING OFF PER SECOND. аS LONG AS YOU KEEP YOUR CODE SHORT (SO YOUR INTERRUPTS DON'T TAKE TOO LONG, AND HAVE ANOTHER INTERRUPT OCCUR BEFORE THE CURRENT ONE IS DONE - MESSY), IT WILL WORK BEAUTIFULLY. сO FAR, THIS IS ALL TALK. лET'S WRITE A FEW SHORT CODE SEGMENTS TO ACCOMPLISH SOME OF THE FEATS WE'VE JUST DISCUSSED. тHE FIRST WE'LL DO IS A RE-HASH OF THE ONE PRESENTED ABOVE. иT FLASHES THE BORDER AGAIN. иT DOES NOT DO ANY MID-SCREEN CHANGES OF VIDEO MODES OR ANYTHING FANCY LIKE THAT, SO ONLY 1 INTERRUPT PER SCREEN IS REQUIRED (IE. 60 PER SECOND, NOT 120 ETC.). тHIS PROGRAM SIMPLY SHOWS THE SAME IDEA, BUT THIS TIME USING VIDEO INTERRUPTS AS THE SOURCE RATHER THAN THE циа. ыOU PROBABLY WON'T NOTICE A DIFFERENCE DURING EXECUTION. ---------------------------------------------------------------------------- ; FLASHER - PART ии ; ; THIS PROGRAM CAUSES THE BORDER TO FLASH 60 TIMES PER SECOND ; THE SOURCE OF THE INTERRUPTS IS THE VIDEO CHIP ; SETUP = * SEI ; DISABLE INTERRUPTS LDA #$7F ; TURN OFF THE CIA INTERRUPTS STA $DC0D LDA $D01A ; ENABLE RASTER IRQ ORA #$01 STA $D01A LDA $D011 ; CLEAR HIGH BIT OF RASTER LINE AND #$7F STA $D011 LDA #100 ; LINE NUMBER TO GO OFF AT STA $D012 ; LOW BYTE OF RASTER LINE LDA #>INTCODE ; GET LOW BYTE OF TARGET ROUTINE STA 788 ; PUT INTO INTERRUPT VECTOR LDA #INTCODE ... RTS - рE-VECTORS THE INTERRUPT CODE TO THE NEW CODE. INC $D020 - цHANGES THE BORDER COLOUR. LDA $D019 STA $D019 - тHESE LINES CLEAR THE BIT IN THE INTERRUPT REGISTER WHICH TELLS THE SOURCE OF THE INTERRUPT (IN PREPERATION FOR THE NEXT). LDA #100 STA $D012 - тHIS LINE RESETS THE RASTER LINE TO GO OFF AT LINE NUMBER 100 AGAIN (SAME AS ABOVE). иT SHOULD BE RESET, SO THE NEXT INTERRUPT WILL KNOW WHAT LINE TO OCCUR ON. JMP $EA31 - еXIT BACK TO THE кERNAL рOM. а уSEFUL еXAMPLE ---------------- тHE FOLLOWING IS AN EXAMPLE OF A MORE SOPHISTICATED PIECE OF RASTER CODE. иT MAKES THE TOP HALF OF THE SCREEN BORDER WHITE, AND THE BOTTOM HALF BLACK. --------------------------------------------------------------------------- SETUP = * ; SOME EQUATES цолоур1 = 0 цолоур2 = 1 лине1 = 20 лине2 = 150 ; CODE STARTS SETUP = * SEI ; DISABLE INTERRUPTS LDA #$7F ; TURN OFF THE CIA INTERRUPTS STA $DC0D LDA $D01A ; ENABLE RASTER IRQ ORA #$01 STA $D01A LDA $D011 ; CLEAR HIGH BIT OF RASTER LINE AND #$7F STA $D011 LDA #лине1 ; LINE NUMBER TO GO OFF AT STA $D012 ; LOW BYTE OF RASTER LINE LDA #>INTCODE ; GET LOW BYTE OF TARGET ROUTINE STA 788 ; PUT INTO INTERRUPT VECTOR LDA # 1. интродуцтион тHIS ARTICLE DISCUSSES THE WELL-UNKNOWN фASTLOAD COMMAND OF THE 1571 AND 1581 DISK DRIVE бURST цOMMAND иNSTRUCTION сET. иF YOU LOOK IN THE BACK OF YOUR '71 (OR '81 и PRESUME) DISK DRIVE MANUAL, YOU WILL FIND THAT THE INFORMATION GIVEN ABOUT THE фASTLOAD UTILITY IS NOT EXACTLY ABUNDANT. тHE фASTLOAD COMMAND WAS INTENDED TO LOAD PROGRAM FILES INTO MEMORY FOR EXECUTION, BUT IT CAN BE USED JUST AS WELL FOR READING THROUGH SEQUENTIAL FILES THAT WOULD BE MUCH TOO LARGE TO LOAD INTO A SINGLE BANK OF INTERNAL MEMORY. тO MAKE USE OF THE фASTLOAD BURST COMMAND, и IMPLEMENT A WORD COUNTING UTILITY THAT WILL COUNT THE NUMBER OF LINES, WORDS, AND CHARACTERS IN A TEXT FILE ON A 1571 OR 1581 DISK DRIVE. тHE ADVANTAGE OF USING THE фASTLOAD COMMAND OVER REGULAR SEQUENTIAL FILE ACCESSING THROUGH THE KERNEL AND дос IS THAT THE фASTLOAD OPERATES ABOUT 3.5 TIMES FASTER ON BOTH DRIVES. 2. ворд цоунтинг утилиты тO USE THE WORD COUNTING PROGRAM, лоад AND рун IT LIKE A REGULAR басиц PROGRAM. иT WILL ASK YOU FOR THE NAME OF A FILE. еNTER THE NAME IF IT IS ON DEVICE NUMBER 8, OR PUT A ONE CHARACTER PREFIX AND A ":" IF IT IS ON ANOTHER DEVICE. а "B" MEANS DEVICE 9, "C" DEVICE 10, ETC. тHE FOLLOWING ARE EXAMPLES OF VALID NAMES: . FILENAME "FILENAME" ON DEVICE 8 . B:FILENAME "FILENAME" ON DEVICE 9 . A:FILENAME "FILENAME" ON DEVICE 8 тHE FILE MUST BE ON EITHER A 1571 OR 1581 DISK DRIVE; THE PROGRAM WILL NOT WORK WITH NON-BURST DEVICES. тHE PROGRAM WILL WORK WITH EITHER прг OR сея FILES, SINCE THE фASTLOAD COMMAND CAN BE TOLD NOT TO WORRY ABOUT THE FILE TYPE. и USE THE SAME DEFINITION OF A WORD AS THE уNIX "WC" COMMAND USES: A SEQUENCE OF CHARACTERS DELIMITED BY WHITESPACE, WHERE WHITESPACE IS DEFINED TO BE спаце, таб, AND невлине (цARRIAGE рETURN) CHARACTERS. тO GET THE LINE COUNT, и SIMPLY COUNT THE NUMBER OF невлинеS. иF THE LAST LINE OF THE FILE DOES NOT END WITH A невлине CHARACTER, THEN THE COUNT WILL BE ONE LINE SHORT. тHIS IS THE SAME AS THE уNIX WC COMMAND TOO. а PROPER TEXT FILE SHOULD HAVE ITS LAST LINE END WITH A невлине CHARACTER. оN MY йIFFYдос-IFIED 1571 AND 1581, и AM ABLE TO ACHIEVE A WORD COUNTING SPEED OF 5,400 CHARS/SEC AND 6,670 CHARS/SEC, RESPECTIVELY. и AM NOT SURE HOW MUCH OF A DIFFERENCE йIFFYдос MAKES, BUT и AM NOT WILLING TO RIP OUT THE ромS TO CHECK. и TESTED USING A 318к FILE. 3. бурст реад либрары тHIS SECTION PRESENTS THE BURST READING LIBRARY THAT YOU CAN INCORPORATE INTO YOUR OWN PROGRAMS AND DESCRIBES HOW THE BURST COMMANDS WORK. тHE LIBRARY HAS THREE CALLS: . BURSTоPEN ( .а=дEVICE, .ь=нAMEлEN, BURSTбUF=фILENAME ) : . BURSTрEAD () : BURSTбUF, BURSTсTATUS, BURSTбUFцOUNT . BURSTцLOSE () и DEFINE THREE COMMON STORAGE VARIABLES FOR USING THIS PACKAGE: "BURSTбUF", "BURSTсTATUS", AND "BURSTбUFцOUNT". "BURSTбUF" IS A 256 BYTE AREA WHERE THE DATA READ IN FROM THE DISK DRIVE IS STORED BEFORE PROCESSING, AND IS LOCATED AT $0б00. "BURSTсTATUS" IS A ZERO-PAGE LOCATION THAT KEEPS THE STATUS RETURNED FROM THE BURST COMMAND SYSTEM. тHIS IS NEEDED BY THE USER TO DETECT WHEN THE END OF FILE HAS BEEN ENCOUNTERED. "BURSTбUFцOUNT" GIVES THE NUMBER OF DATA BYTES AVAILABLE IN "BURSTбUF" AFTER AN OPEN OR READ OPERATION. иTS VALUE WILL BE SOMEWHERE BETWEEN 1 AND 254. а FULL SECTOR CONTAINS 254 BYTES OF DATA AND TWO BYTES OF CONTROL INFORMATION. "BURSTсTATUS" AND "BURSTбUFцOUNT" ARE DEFINED TO BE AT LOCATIONS $фе AND $фф, RESPECTIVELY. ыOU ARE ALLOWED TO ALTER THE VALUES OF THE TWO VARIABLES AND THE DATA BUFFER BETWEEN CALLS, IF YOU WISH. фOR REASONS NOT COMPLETELY UNDERSTOOD, INTERRUPTS MUST BE DISABLED FOR THE ENTIRE COURSE OF BURST READING A FILE. и SUSPECT THIS IS BECAUSE THE иря SERVICE ROUTINE READS THE INTERRUPT MASK REGISTER OF циа#1, THUS CLEARING THE сERIALдATAрEADY FLAG THAT THE BURST READ ROUTINE WAITS FOR. аNYWAY, THE OPEN ROUTINE DOES A сеи AND THE CLOSE ROUTINE DOES A цли, SO YOU DON'T HAVE TO DO THIS YOURSELF. иF AN ERROR OCCURS DURING THE EXECTION OF ONE OF THESE ROUTINES, IT WILL RETURN WITH THE CARRY FLAG SET AND WITH THE ERROR CODE IN THE .а REGISTER (SAME AS THE KERNEL (YES, и KNOW THAT цOMMODORE LIKES TO CALL IT THE "KERNаL")). еRROR CODES 0 TO 9 CORRESPOND TO THE STANDARD KERNEL CODES, ERROR CODE 10 MEANS THAT THE DEVICE IS NOT A BURST DEVICE, AND ERROR CODES 16 TO 31 CORRESPOND TO THE BURST CONTROLLER STATUS CODES 0-15. иF NO ERROR OCCURS, THE ROUTINES RETURN WITH THE CARRY FLAG CLEAR, OF COURSE. оNLY ONE FILE MAY BE OPEN AT A TIME FOR фASTLOADING, SINCE фASTLOAD TAKES OVER THE DISK DRIVE AND THE ENTIRE SERIAL BUS. еVEN REGULAR FILES CANNOT BE ACCESSED WHILE A FASTLOAD IS IN PROGRESS. тHUS, фASTLOAD IS NOT SUITABLE FOR ALL FILE PROCESSING APPLICATIONS, BUT IT WORKS VERY WELL FOR READING A FILE INTO MEMORY (LIKE FOR A TEXT EDITOR) AND FOR SUMMARIZATION OPERATIONS (LIKE WORD COUNTING). тHE BURST LIBRARY REQUIRES THAT THE KERNEL AND и/о SPACE BE IN CONTEXT WHEN IT IS CALLED. 3.1. бурст опен тHE WAY THAT A BURST COMMAND IS GIVEN IS TO GIVE A MAGICAL INCANTATION OVER THE COMMAND CHANNEL TO THE DISK DRIVE. ыOU CAN EITHER USE THE LOW-LEVEL SERIAL BUS CALLS (листн, сецнд, циоут, AND унлсн) OR USE THE опен AND цхроут CALLS. и USED THE LOW LEVEL CALLS FOR A LITTLE EXTRA ZIP. тHE BURST COMMAND FORMAT FOR фASTLOAD IS GIVEN IN THE BACK OF YOUR DRIVE MANUAL: . быте \ BIT: 7 6 5 4 3 2 1 0 э жALUE . -------+--------+-----+-----+-----+-----+-----+-----+-----+------- . 0 э 0 э 1 э 0 э 1 э 0 э 1 э 0 э 1 э "у" . 1 э 0 э 0 э 1 э 1 э 0 э 0 э 0 э 0 э "0" . 2 э п э ь э ь э 1 э 1 э 1 э 1 э 1 э 159 . 3 - ?? э э . -------+--------------------------------------------------+------- WHERE "ь" MEANS "DON'T CASE" AND "п" MEANS "PROGRAM". иF THE п BIT IS '0' THEN ONLY PROGRAM (прг) FILES CAN BE LOADED, AND IF IT IS '1' THEN SEQUENTIAL (сея) FILES CAN BE LOADED AS WELL. тHE PACKAGE AUTOMATICALLY SETS THIS FLAG FOR YOU. нOTE THAT YOU DON'T HAVE TO DO AN иNQUIRE дISK OR яUERY дISK фORMAT IN ORDER TO USE THIS COMMAND LIKE YOU HAVE TO DO WITH THE BLOCK READING AND WRITING COMMANDS. иF YOU WANT TO TRY GIVING THE INCANTATION YOURSELF, ENTER: опен1,8,15,"у0"+цхр$(159)+"филенаме" (WHERE "филенаме" IS THE NAME OF SOME FILE THAT EXISTS ON YOUR DISK) ON YOUR 128 AND YOUR DISK DRIVE WILL SPRING TO LIFE AND WAIT FOR YOU TO READ THE FILE DATA. ыOU CAN'T READ THE DATA FROM басиц, SO TO CANCEL THE COMMAND: цлосе1 тHE "BURSTоPEN" CALL OF THIS PACKAGE ACCEPTS THE NAME OF THE FILE TO BE LOADED AT THE START OF THE "BURSTбUF" BUFFER, THE LENGTH OF THE FILENAME IN THE .ь REGISTER, AND THE DEVICE NUMBER TO LOAD THE FILE FROM IN THE .а REGISTER. тHE BURST COMMAND HEADER AND THE FILENAME ARE SENT TO THE DISK DRIVE AS DESCRIBED ABOVE. тHE OPEN COMMAND ALSO READS THE FIRST SECTOR OF THE FILE, FOR TWO REASONS. фIRST, THE STATUS BYTE RETURNED FOR THE FIRST SECTOR HAS SPECIAL MEANING. сTATUS CODE $02 MEANS "FILE NOT FOUND". тHE PACKAGE TRANSLATES THIS INTO THE KERNEL ERROR CODE. сECOND, AND MOST IMPORTANT, THERE IS A BIZARRE FEATURE (READ: "BUG") IN THE фASTLOAD COMMAND. иF THE FILE TO BE READ IS ONLY ONE BLOCK LONG, THEN THE NUMBER OF BYTES REPORTED FOR THE BLOCK LENGTH IS TWO BYTES TOO SHORT. тHE FOLLOWING TABLE GIVES THE NUMBER OF BYTES REPORTED AND THE NUMBER OF ACTUAL BYTES IN THE SECTOR: . аCTUAL э 4 э 3 э 2 э 1 э 0 э . ---------+---------+---------+---------+---------+---------+ . рEPORTED э 2 э 1 э 0 э 255 э 255 э тHIS IS WHERE и RAN INTO PROBLEMS WITH зED-128; THE LOGIC OF MY PROGRAM SCREWED UP ON A ZERO LENGTH. и HAVE CORRECTED THE PROBLEM HERE, THOUGH. тHIS BUG IS BIZARRE BECAUSE IT ONLY HAPPENS IF THE FIRST SECTOR IS THE ONLY SECTOR IN THE FILE. тHE REPORTED LENGTH FOR ALL SUBSEQUENT SECTORS IS CORRECT. нOTE ALSO THAT 255 IS REPORTED FOR LENGTHS OF BOTH 1 AND 0. тHIS IS BECAUSE THERE IS NO ACTUAL ZERO LENGTH FOR цOMMODORE FILES. иF YOU опен1,8,2,"емпты" AND THEN IMMEDIATELY цлосе1 YOU GET A FILE WITH ONE CARRIAGE RETURN CHARACTER IN IT. тHE OPEN ROUTINE CALLS THE READ ROUTINE TO READ A SECTOR AND IF IT WAS THE ONLY SECTOR OF THE FILE, THE TWO ADDITIONAL BYTES ARE BURST-READ AND PUT INTO THE DATA BUFFER. нOTE THAT INCREMENTING THE REPORTED COUNT OF 255 TWICE GIVES THE CORRECT COUNT OF 1. аLSO INTERESTING IN THIS CASE IS THAT WHEN THE 1571/81 REPORTS THE 255, IT ACTUALLY TRANSFERS 255 BYTES OF DATA, ALL OF WHICH ARE BOGUS. иT SEEMS TO ME THAT THEY MADE THE 1581 BUG-COMPATIBLE WITH THE 1571 IN THIS RESPECT. тHE OPEN ROUTINE ALSO EXECUTES A сеи FOR REASONS DISCUSSED ABOVE. тHE INFORMATION RETURNED BY THE OPEN CALL IS THE SAME AS WHAT IS RETURNED FOR THE "BURSTрEAD" CALL DISCUSSED NEXT. 3.2. бурст реад оNCE THE фASTLOAD COMMAND IS STARTED, THE DRIVE STARTS WAITING TO TRANSFER THE DATA TO YOU. тHE TRANSFER OCCURS SECTOR BY SECTOR, WITH EACH SECTOR PRECEEDED BY A BURST STATUS BYTE. тHE DATA IS TRANSFERRED USING THE SHIFT REGISTER OF циа#1 AND THE HANDSHAKING IS DONE USING THE сLOW сERIAL цLOCK LINE OF циа#2. тO RECEIVE A BYTE, YOU TOGGLE THE сLOW сERIAL цLOCK LINE AND WAIT FOR THE сHIFT рEGISTER рEADY SIGNAL FROM циа#1 AND THEN READ THE DATA VALUE FROM THE SHIFT DATA REGISTER. оNE OF THE CLOCK REGISTERS IN THE циа IN THE 1571/81 IS USED AS THE BAUD RATE GENERATOR FOR THE SERIAL LINE. и THINK THAT IT USES A DELAY OF 4 MICROSECONDS PER BIT, WHICH GIVES A BAUD RATE OF 250,000 (31.25к/SEC). иN MY EXPERIMENTATION, THE MAXIMUM BAUD RATE и HAVE EVER ACHIEVED IN REALITY IS 200,000 (25к/SEC). и READ IN MY 1571 иNTERNALS BOOK THAT THE 250,000 BAUD RATE CANNOT ACTUALLY BE ACHIEVED BECAUSE OF ELECTRICAL PROBLEMS THAT и DON'T UNDERSTAND. тHIS IS AN IMPORTANT DIFFERENCE BECAUSE THE DATA COMES FLYING OFF THE SURFACE OF THE DISK AT AROUND 30к/SEC AND IF THE SERIAL BUS WERE FAST ENOUGH, IT COULD BE TRANSFERRED TO THE COMPUTER AS IT IS BEING READ. сOME THINGS WOULD BE SO MUCH MORE CONVENIENT IF WHOMEVER CREATED THE UNIVERSE HAD THOUGHT TO MAKE LIGHT GO JUST A LITTLE BIT FASTER. тHE BURST HANDSHAKING PROTOCOL SLOWS THE MAXIMUM TRANSFER RATE DOWN TO ABOUT 16к/SEC. оF COURSE, THE DISK DRIVE HAS MORE THINGS TO KEEP ON TOP OF THAN JUST TRANSFERRING DATA, SO THE ACTUAL BURST THROUGHPUT IS LOWER THAN THAT: ABOUT 5.4к/SEC WITH MY йIFFYдос-IFIED 1571 AND ABOUT 7к/SEC WITH A 1581. нOTE THAT YOU CAN PROBABLY INCREASE YOUR 1571'S BURST PERFORMANCE A BIT BY SETTING IT TO USE A SECTOR INTERLEAVE FACTOR OF 4, USING THE "у0>с"+цхр$(I) BURST COMMAND. бY DEFAULT, A 1571 WRITES FILES WITH AN INTERLEAVE OF 6. аLL OF THE SECTORS BEFORE THE LAST ONE WILL CONTAIN 254 BYTES OF DATA AND THE LAST ONE WILL CONTAIN A SPECIFIED NUMBER OF BYTES, FROM 1 TO 254. тHE STATUS CODE RETURNED FOR THE LAST SECTOR IS VALUE $1ф. иN THIS CASE, AN ADDITIONAL BYTE IS SENT BEFORE THE DATA BYTES THAT TELLS HOW MANY DATA BYTES THERE WILL BE. тHIS IS THE VALUE THAT IS BUGGED FOR ONE-SECTOR FILES AS DESCRIBED IN THE LAST SECTION. фOR THOSE WHO LIKE PICTURES, HERE ARE DIAGRAMS OF THE DATA TRANSFERRED FOR A SECTOR: . регулар сецтор ласт сецтор оф филе . +-------------------+ +--------------------+ . 0 э бURST сTATUS бYTE э 0 э бURST сTATUS = $1ф э . +-------------------+ +--------------------+ . 1 э э 1 э бYTE цOUNT = н э . ... + 254 дATA бYTES э +--------------------+ . 254 э э 2 э э . +-------------------+ ... э н дATA бYTES э . н+1 э э . +--------------------+ иF A SECTOR RETURNS A BURST STATUS CODE OTHER THAN 0 (OK) OR $1ф (END), THEN AN ERROR HAS OCCURRED AND THE DISK DRIVE ABORTS THE TRANSFER, CLOSES THE BURST CONNECTION, AND STARTS THE DRIVE LIGHT BLINKING. тHE "BURSTрEAD" CALL OF THIS PACKAGE READS THE DATA OF THE NEXT SECTOR OF THE OPENED FILE INTO THE "BURSTбUF" AND RETURNS THE "BURSTсTATUS" AND "BURSTбUFцOUNT" (BYTES READ). иN THE EVENT OF AN ERROR OCCURING, THIS ROUTINE RETURNS WITH THE CARRY FLAG SET AND THE TRANSLATED BURST ERROR CODE IN THE .а REGISTER (SAME AS BURSTоPEN). вHEN THE LAST SECTOR OF THE FILE HAS JUST BEEN READ, THIS ROUTINE RETURNS WITH A VALUE OF $1ф IN THE "BURSTсTATUS" VARIABLE. 3.3. бурст цлосе аFTER READING THE LAST DATA BYTE OF THE LAST SECTOR OF THE FILE, THE BURST CONNECTION AND IS CLOSED AUTOMATICALLY BY THE DISK DRIVE. тHE "BURSTцLOSE" ROUTINE IS NOT NECESSARY FOR COMMUNICATION WITH THE DISK DRIVE, BUT IS PROVIDED FOR COMPLETENESS AND TO CLEAR THE INTERRUPT DISABLE BIT (цли) THAT THE OPEN ROUTINE SET TO PREVENT INTERRUPTS WHILE BURST READING.