In This Issue...
Subscription Renewals
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New Macro Cross Assemblers Available
The high cost of dedicated microprocessor development systems has forced many technical people to look for alternate methods to develop programs for the various microprocessors. Combining your very versatile Apple II with the S-C Macro Assembler provides a cost effective and powerful development system.
There are now three cross-assembler modules ready for the S-C
Macro Assembler, and more to come. Each cross-assembler disk
costs $32.50 to registered owners of the S-C Macro Assembler.
You get both regular and language card versions, with
documentation of the special features and differences.
The 6809 cross-assembler is designed to work with the Stellation Mill. The MGO command starts the 6809 processor executing your assembled object code. Likewise, the Z-80 version is designed to work with the Microsoft Softcard.
We have begun working on a Motorola 68000 version....
When writing an editor or other single-keystroke command system, a very common need is a subroutine which branches according to the value of a character. In Pascal and some other languages there is even a special statement for this programming need: CASE. You might do it like this in Applesoft:
1000 GET A$
1010 IF A$ = "A" THEN 2000
1020 IF A$ = "C" THEN 3000
1030 et cetera
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You will often find the equivalent code in assembly language programs:
1000 LDA CHARACTER
1010 CMP #'A
1020 BEQ CHAR.WAS.A
1030 CMP #'C
1040 BEQ CHAR.WAS.C
1050 et cetera
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Of course, it frequently happens that the number of different values is small, and the code sequence above with several CMP-BEQ pairs is the most efficient. It loses a little of its appeal, though, when you have to do it for more than about ten different values. And what if the branch points are too far away for BEQ relative branches? Then you have to write:
1000 LDA CHARACTER
1010 CMP #'A
1020 BNE .1
1030 JMP CHAR.WAS.A
1040 .1 CMP #'C
1050 BNE .2
1060 JMP CHAR.WAS.C
1070 .2 et cetera
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That takes seven bytes of program for each value of the character.
Personally, I like to put the possible values and the corresponding branch addresses in a table, and search that table whenever necessary. Each table entry takes only three bytes. If the subroutine is used with several tables, and if there are a lot of possible values, then the tabular method saves a lot of memory.
I used the tabular method in my still-in-development word-processor. To speed and simplify the coding of the table entries, I wrote a macro definition JTBL as follows:
1020 .MA JTBL
1030 .DA #$]1,]2-1
1040 .EM
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This defines a macro JTBL with two parameters. The first one will be the hexadecimal value to compare the test-character with, and the second one will be the branch address for that value. For example, if I write the macro call:
1400 >JTBL 86,FLIP.CHARS
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the S-C Macro Assembler will generate:
.DA #$86,FLIP.CHARS-1
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The "-1" is appended to each branch address in the table, because I use the PHA-PHA-RTS method to perform the branch. Before I go any farther, here is the search and branch subroutine:
1220 SEARCH.AND.PERFORM.NEXT
1230 INY POINT TO NEXT ENTRY
1240 INY
1250 INY
1260 SEARCH.AND.PERFORM
1270 LDA T.BASE,Y GET VALUE FROM TABLE
1280 BEQ .1 NOT IN THE TABLE
1290 CMP CURRENT.CHAR
1300 BNE SEARCH.AND.PERFORM.NEXT
1310 .1 LDA T.BASE+2,Y LOW-BYTE OF BRANCH
1320 PHA
1330 LDA T.BASE+1,Y HIGH-BYTE OF BRANCH
1340 PHA
1350 LDY #0 (SINCE MOST BRANCHES WANT Y=0)
1360 RTS DO THE BRANCH!
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There are so far four different value-branch tables in my word processor. Here is an abbreviated listing:
1380 T.BASE
1390 T.ESC0 >JTBL 81,AUXILIARY.MENU
1400 >JTBL 82,SCAN.BEGIN
1410 >JTBL 83,TOGGLE.CASE.LOCK
. . . . . .
1540 >JTBL 9B,ESC0.ESC
1550 >JTBL 00,SC.BELL
1560 *--------------------------------
1570 T.ESC2 >JTBL 81,AUXILIARY.MENU
. . . . . .
1690 >JTBL EB,SCAN.RIGHT
1700 >JTBL ED,SCAN.DOWN
1710 >JTBL 00,ESC2.END
1720 *--------------------------------
1730 T.MAIN >JTBL C4,MAIN.DOS
1740 >JTBL C5,MAIN.EDIT
. . . . . .
1800 >JTBL D3,MAIN.SAVE
1810 >JTBL 00,MON.BELL
1820 *--------------------------------
1830 T.AUX >JTBL C3,COPY.BLOCK
1840 >JTBL C4,DELETE.BLOCK
. . . . . .
1890 >JTBL D3,SAVE.SEGMENT
1900 >JTBL 00,SC.BELL
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Notice that each of the four tables ends with a 00 value. The branch address after the 00 value tells where to branch if the current character does not match any values in the table.
When I want to compare the current character with entries in the T.MAIN table, here is how I do it:
2000 LDY #T.MAIN-T.BASE
2010 JSR SEARCH.AND.PERFORM
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The LDY instruction sets Y to the offset of the table from T.BASE, and the search subroutine references the table relative to T.BASE. I use JSR to call the search subroutine. The search subroutine uses PHA-PHA-RTS to effectively JMP to the chosen branch address. And then the value processor ends with RTS to return to the next line after the JSR SEARCH.AND.PERFORM.
Counting all four tables, I have 45 branches, occupying 3*45 = 135 bytes. If I had used the CMP-BEQ method, which occupy four bytes per value, it would have taken 4*45 = 180 bytes. The subroutine is only 23 bytes long, so I saved 22 bytes. But if I needed the longer CMP-BNE-JMP sequences throughout, I would have had 7*45 = 315 bytes! Wow! Long live tables!
Tables have even more advantages. For one, they are a lot easier to modify when you want to add or delete a value. For another, the program is easier to read when there is no rat's nest of branches to try to unravel. For me, it almost makes the assembly listing as easy to read as the reference manual!
Notice that it would be possible to overlap tables using my subroutine. I might need at some times to search for 13 different values, and at others to search for only 7 of those same values, with the same branches. If so, the seven entries in common would be grouped at the end of the 13-entry table. The table has two labels, like this:
3000 T.13 >JTBL C1,DO.A
3010 >JTBL C4,DO.D
. . . . .
3050 >JTBL CF,DO.O
3060 T.7 >JTBL C2,DO.B
3070 >JTBL C5,DO.E
. . . . .
3120 >JTBL D7,DO.W
3130 >JTBL 00,DO.NOTHING
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What about speed? Well, it is pretty fast too. The CMP-BNE-JMP takes five cycles for each value that does not compare equal, and finally seven cycles for the one which compares equal. If the tenth comparison bingos, that is 9*5+7 = 52 cycles. The subroutine takes 171 cycles for the same search. Over three times longer, but still less that 120 microseconds longer. You would have to perform the search over 8000 times in one day to add a whole second of computer time!
Here is a small program to accompany Bill Morgan's Automatic Catalog in the June '82 issue of AAL. This routine adds an AUTO/MANUAL command toggle to the S-C Macro Assembler. Using CTRL-A when the cursor is at the beginning of a line enters the AUTO line numbering mode and waits for input of a line number and/or RETURN. Entering another CTRL-A while in AUTO mode and at the start of a line executes a MANUAL command.
In addition, I have added some code to provide slow and fast listings at a single keypress. CTRL-S does a SLOW LIST command, which is cancelled by a 'RETURN' during listing. CTRL-L will provide a listing at normal speed (assuming the slow list has been cancelled.)
The patch is implemented as follows:
1. Enter the S-C Macro Assembler
2. :$101D:33 N 1000G
3. :BLOAD AUTO/MANUAL PATCH
4. :$138D: 4C 28 32 (JMP PATCH instead of JSR BELL)
5. :BSAVE AUTO/MAN S-C MACRO ASM,A$1000,L$2300
Note: You may omit step 2 if you have already installed Bill's automatic CATALOG.
1000 *-------------------------------- 1010 * AUTO/MANUAL TOGGLE 1020 * 1030 * BY ROBERT F. O'BRIEN 1040 * 14, CLONSHAUGH LAWN, DUBLIN 5. 1050 *-------------------------------- 1060 .OR $3228 1070 .TF AUTO/MANUAL PATCH 1080 *-------------------------------- 1090 CH .EQ $24 1100 SC.SLOW .EQ $11D2 1110 SC.REENTER .EQ $135E 1120 SC.RETURN .EQ $13C3 1130 SC.INSTALL .EQ $152A 1140 SC.LIST .EQ $183F 1150 MON.BELL .EQ $FF3A 1160 *-------------------------------- 1170 AUTO.MANUAL.COMMAND 1180 CMP #$81 CTRL-A? 1190 BEQ AUTO.TOGGLE 1200 CMP #$8C CTRL-L? 1210 BEQ LIST 1220 CMP #$93 CTRL-S? 1230 BEQ SLOW.LIST 1240 * 1250 BACK JSR MON.BELL 1260 JMP SC.REENTER BACK TO ASSEMBLER 1270 *-------------------------------- 1280 AUTO.TOGGLE 1290 LDA CH 1300 CMP #1 BEGINNING OF LINE? 1310 BEQ AUTO.CMD 1320 CMP #6 AFTER LINE NUMBER? 1330 BEQ MANUAL.CMD 1340 BNE BACK 1350 *-------------------------------- 1360 AUTO.CMD 1370 LDX #0 1380 .1 LDA AUTO.TEXT,X GET CHARACTER 1390 JSR SC.INSTALL PROCESS CHAR 1400 CPX #5 1410 BCC .1 1420 JMP SC.REENTER 1430 AUTO.TEXT .AS -/AUTO / 1440 *-------------------------------- 1450 MANUAL.CMD 1460 LDX #0 1470 STX CH GO TO START OF LINE 1480 .1 LDA MANUAL.TEXT,X 1490 JSR SC.INSTALL 1500 CPX #6 1510 BCC .1 1520 JMP SC.RETURN 1530 MANUAL.TEXT .AS -/MANUAL/ 1540 *-------------------------------- 1550 LIST LDA CH 1560 CMP #1 BEGINNING OF LINE? 1570 BNE BACK 1580 JSR SC.LIST 1590 JMP SC.RETURN 1600 *-------------------------------- 1610 SLOW.LIST 1620 LDA CH 1630 CMP #1 1640 BNE BACK 1650 JSR SC.SLOW SET SLOW MODE 1660 JSR SC.LIST 1670 JMP SC.RETURN |
Volume 5, Number 6 of Call A.P.P.L.E. has an article giving a DOS patch to replace the volume number printed during catalog with number of free sectors remaining on the disk.
The routine as published works for both Applesoft and Integer BASIC, but does not work with the language card version of the S-C Assembler. Only a few changes were needed to make it work with all three.
A call to Bob gave me the location of the decimal print routine in the S-C Macro Assembler, Language Card Version.
The original code as published in CAll A.P.P.L.E. checked location $E006 to see what language is in use. My code looks at $E001, which has a different value in each of the three:
Language $E001
--------------------------
Applesoft: $28
Integer BASIC: $00
S-C Macro Assembler: $94
The code in lines 1320-1370 checks which language is in use and jumps to the right routine. I also changed the zero page locations used to count the number of free sectors because the S-C Assembler print routine expects the two-byte value to be in $D3 and $D4.
The rest of the code works as explained in the Call A.P.P.L.E. article. I refer you to it for more details and as an excellent lesson on reducing the size of code.
Install the two patches to DOS by BLOADing the two binary files FREE.SECTORS.1 and FREE.SECTORS.2. The type CATALOG to see the how many free sectors you have.
1000 *SAVE S.FREE SECTORS 1010 *-------------------------------- 1020 * FREE SECTORS PATCH FOR DOS 3.3 1030 *-------------------------------- 1040 LOBYTE .EQ $D3 1050 HIBYTE .EQ $D4 1060 *-------------------------------- 1070 SECTOR.MAP .EQ $B3F2 1080 LANG.ID .EQ $E001 LANGUAGE ID 1090 PRT.INT .EQ $E51B INTEGER BASIC PRINT ROUTINE 1100 PRT.FP .EQ $ED24 APPLESOFT PRINT ROUTINE 1110 PRT.SC .EQ $DE00 S-C ASSEMBLER PRINT ROUTINE 1120 *-------------------------------- 1130 .OR $BA69 1140 .TF FREE.SECTORS.1 1150 *-------------------------------- 1160 FREE.SECTOR.PATCH 1170 LDY #$C8 1180 .1 LDA SECTOR.MAP,Y 1190 BEQ .4 NO FREE SECTORS IN THIS BYTE 1200 .2 ASL SHIFT INTO CARRY 1210 BCC .2 SECTOR IN USE 1220 PHA SECTOR FREE 1230 INC LOBYTE COUNT IT 1240 BNE .3 1250 INC HIBYTE 1260 .3 PLA SECTOR MAP BYTE AGAIN 1270 BNE .2 IF ANY LEFT 1280 .4 DEY NEXT BYTE OF SECTOR MAP 1290 BNE .1 1300 LDX LOBYTE VALUE IN X AND A 1310 LDA HIBYTE 1320 LDY LANG.ID CHECK WHICH LANGUAGE 1330 BMI SCASM $94: S-C ASSEMBLER 1340 BEQ INTEGR $00: INTEGER BASIC 1350 JMP PRT.FP $28: APPLESOFT 1360 INTEGR JMP PRT.INT 1370 SCASM JMP PRT.SC 1380 *-------------------------------- 1390 .OR $ADB9 1400 .TF FREE.SECTORS.2 1410 *-------------------------------- 1420 NOP FILLER 1430 LDA #0 ZERO THE COUNT 1440 STA LOBYTE 1450 STA HIBYTE 1460 JSR FREE.SECTOR.PATCH 1470 *-------------------------------- |
It seems that whenever I purchase a new hardware product for my Apple, I spend countless hours honing my most precious software tools to make them compatible with it. I purchased my Videx Videoterm card for use with Pascal, and had no intention of using it with the S-C Assembler. Then one fateful day I made a temporary patch to Version 4.0 -- just to see what it would look like -- and I was immediately hooked....
You won't believe what it's like to assemble with 80 columns of display! You can actually write source files that are legible on the screen, with no wraparound on comments -- even during assembly. What you see on the display is what you would see on a printer, only cleaner.
When I upgraded to the S-C Macro Assembler, I was compelled to produce a configuration file that would modify the new assembler to work with the Videoterm board. The resulting source file is included with this article.
The assembled SCM80 file will reconfigure a copy of the S-C Macro Assembler Version 1.0 that is currently resident in memory (for more about this concept, see "Controlling Software Configuration", AAL April '82).
Once the mods are installed you will be able to use your Videx for everything except: (1) Using the Escape-L sequence to LOAD a disk file whose name appears on the display, and (2) Using the copy key (right arrow). You will still be able to use Escape-L to generate the normal dashed comment line, and you can use the other escape functions to move the cursor and clear portions of the screen.
SCM80 will display control characters (and other selected strings intended to be so) in inverse on your screen, provided you have the standard (inverse) alternate character generator ROM installed in your Videoterm. If you have some other ROM installed, these characters and strings may be printed in Chinese. In this case you may want to modify the new character output routine!
SCM80 will also permit painless switching of case while using the assembler. A control-A keypress will always be recognized as a "shift lock" signal, while a control-Z will be treated as a "shift unlock". This feature makes it easy to write easy-to-read source files.
The assembled SCM80 code is moved into memory immediately following the assembler, and is located at one of two places, depending on which flavor (vanilla or language card) of the assembler you're using. The flavor of the configuration file is made to match that of the assembler through the use of a conditional flag (LCVERSION) and several conditional assembly statements. Another equate variable, SLOTNUM, allows you to specify the slot in which your Videx board resides.
How It All Works
There are two primary steps involved in installing the modified code in the assembler: (1) Moving the new code into the area of memory immediately following the assembler, and (2) Patching the existing assembler code to point to the new routines and then returning or cold-starting the system.
The SCM80 code contains both the new Videoterm support routines and the routines used to install those support routines. It loads in at $4000, stuffs the Videoterm routines just beyond the assembler code, and then performs the return or cold start. Depending on the flavor, a few other small tasks are performed in the process; let's take a closer look.
Lines 1280-1310 contain the two constants used to tailor SCM80 to assembler flavor and Videoterm slot number. The last two lines are the starting addresses where the new code will be relocated, depending on the flavor. The LCVERSION flag is used to determine the base address of the assembler in lines 1340-1380; this base address is used throughout the rest of the listing to determine absolute patch addresses within the assembler.
The Videoterm support routines are contained in lines 3240-3770. Lines 3400-3700 contain replacement routines for two of the routines in the line editor portion of the assembler. The NEW.WARM.ENTRY routine in lines 3240-3260 is intended to keep the Videoterm in the saddle during a RESET or system warm start.
The code in lines 3820-4740 are replacements for some of the standard monitor routines. Several of these routines have no other purpose than to support the escape cursor movements. In the case of the language card flavored RDKEY, an extra subroutine is provided to unprotect the RAM during case-shift sequences (more about that in a minute).
Lines 1770-2040 use the monitor's MOVE routine to slip the support routines into their designated origin at $3200 or $F400. The vanilla version patches the assembler's symbol table address to make room for the move; the language card version unprotects RAM prior to the move.
The patching of the assembler is done in lines 2050-2920. unused code is NOP-ed out here, and jumps are strategically poked in to point to the new routines. A replacement escape jump table created in lines 2950-3090 gets installed in the assembler, so the new escape routines can be accessed in the standard manner. The assembler's cold start routines are patched to point to the resilient NEW.WARM.ENTRY routine (more about that in a moment, too).
Lines 2870-2920 complete the installation and patching process. For the vanilla version, a simple RTS returns control to the calling program. The language card version first write protects RAM and then performs a DOS cold start. Once the assembled code has been installed and the patches made, the installation portion of SCM80 is of no use, so a cold start should be performed to reset the assembler's file pointers, leaving only the SCM80 code that is now supporting your Videoterm.
Assembly and Installation
You'll note the absence of any .TF directive in the listing, meaning you'll have to manually save this file when you're done. This is because although the resulting object code will be located in continuous memory, it has origins (.OR directives) at two locations. The actual length of the file is calculated by a variable called LENGTH. The instructions for assembly are contained in the source file's title block. I call my vanilla patch file SCM80, and the language card version SCM80.LC.
With the assembler code resident in memory, there are several ways of installing the patches. Perhaps the most straightforward is to BRUN the assembled patch file, or BLOAD it and type 4000G as a monitor command. If you're using the vanilla assembler, you'll need to force a cold start of the assembler by typing "NEW" or 1000G as a monitor command; this action will ensure all the internal patches have been installed into DOS as well. The language card version cold starts itself, and requires no intervention.
A cleaner way is to use an EXEC file. The following file will bring up the vanilla version of the assembler:
REM LOAD ASM
CALL -151 Enter the monitor
BLOAD S-C.ASM.MACRO Load the Assembler
BLOAD SCM80 Load the patches
4000G Install them, and
1000G Start the assembler!
To load the language card patches with an EXEC file, refer to Bob's EXEC file on the top of Page 4 of the May '82 AAL, and replace "3D3G" with the following two lines:
BLOAD SCM80.LC Load the LC patches
4000G Install them and cold start!
The character I/O is being vectored through routines at the end of the assembler; for the language card version, these routines are somewhere in $F4XX. If you decide to issue an "FP" command from that version, you'll find yourself in "Never-Never Land". It's good practice to issue a "PR#n" first (where "n" is the Videoterm's slot number). When you type "INT" to restart the assembler, the special I/O routines will automatically be hooked in.
A Funny Thing Happened on the Way...
Bob thought it would be enlightening to touch on some some of the crazy things that went on during the development of these routines. I always marvel at people like Bob, Mike, Bill, and Lee, who have a gift for writing machine language, and can sit down and bang out a line editor in a few hours.
The rest of us aren't quite so fortunate. SCM80 took my three days to write, even though I had done some quick patches on Version 4.0. A couple of good ones popped up during that time, and I'll pass them along.
I was determined to interface the Videoterm using only its terminal functions, avoiding any internal Videoterm ROM routines that would make the interface version-dependent (my card matches neither the descriptions nor the ROM source listings contained in my manual!).
The Videoterm will not move its flashing cursor to a GOTOXY Location unless the cursor is first placed there and then a character is output; under BASIC, you can't just HTAB and VTAB to a position and GET a character -- you have to print a character first (even a null character will do it), in order to move the cursor!
After spending several hours fighting with the Videoterm over who was controlling the input and output cursor locations, I finally decided to designate my own locations for CH and CV (normally at $24 and $25) for use by the editing routines.
The other frustration I incurred was doing the case-switching in the replacement RDKEY routine. I was using the language card version, and had carefully checked my code, but the assembler just wouldn't switch case for me. True confession: it took almost fifteen minutes before it dawned on me that the assembler's case flag (at $D016) was write protected! Hence, the special unprotect subroutine called by the new RDKEY.
One final note concerns the contortions in the replacement COUT and WARM.ENTRY routines (at least I saw these coming!). We need to keep our new RDKEY routine in the DOS input hook to keep things working predictably. The Videoterm, when installed by placing it in the output hook and calling it to output a character, takes over the input hook as well. In addition, we have a replacement COUT routine that is designed to detect and modify control characters for display prior to their output.
In order to avoid arm-wrestling with the Videoterm over who controls the input hook, I used a strange but effective technique. During the installation and patch portion, I install the Videoterm in the designated slot, hook it in, and send a bogus character to make sure it has installed its warm entry I/O locations in DOS ( $AA52-$AA56 for 48K machines). The code immediately following uses an internal assembler routine to calculate the address of the DOS output hook, regardless of memory size. The contents of the DOS output hook are then moved into the new COUT routine, immediately following a JMP, and the same COUT routine is forced into the DOS hook, along with the new RDKEY routine. Whenever a character is output, it will first be given to COUT; when COUT has done its work, the character is then passed to the Videoterm's warm entry.
During the installation and patch, the warm start vector within the assembler was modified to point to the NEW.WARM.START routine, which re-installs COUT and RDKEY, keeping everything in sync. A RESET will always restore this condition, no matter what the Videoterm may have in mind!
The S-C Macro Assembler is a wonderful piece of software, and the upgrade is a steal at $27.50. The only thing that can top it is being able to use it with 80 columns of display!
If you find any errors in my patches, or come up with some new features, contact me at (206) 779-9508.
1000 .LIST OFF 1010 *-------------------------------- 1020 * SCM80 1030 * Patches for S-C Macro Assembler V1.0 1040 * for Videx Videoterm Card 1050 * 1060 * Date: 7/10/82 1070 * 1080 * Don Taylor 1090 * infoTool corporation 1100 * Drawer 809, Poulsbo, WA 98370 1110 * 1120 * To assemble this file: 1130 * 1140 * 1. Set SLOTNUM to slot number of videx card 1150 * 1160 * 2. Set LCVERSION flag for 1170 * .EQ 1 for Language card version ($D000) 1180 * .EQ 0 for Standard version ($1000) 1190 * 1200 * 3. Assemble as usual 1210 * 1220 * 4. Use VAL LENGTH to get length in hex 1230 * 1240 * 5. BSAVE SCM80, A$4000, L$LENGTH 1250 * 1260 *-------------------------------- 1270 * 1280 SLOTNUM .EQ 3 VIDEX slot 1290 LCVERSION .EQ 1 SCM80 version 1300 PATCH.AREA .EQ $3200 1310 LC.PATCH.AREA .EQ $F400 1320 * 1330 *-------------------------------- 1340 .DO LCVERSION 1350 SCM.BASE .EQ $D000 1360 .ELSE 1370 SCM.BASE .EQ $1000 1380 .FIN 1390 *-------------------------------- 1400 * Program Constants 1410 *-------------------------------- 1420 MON.CSW .EQ $36 1430 MON.KSW .EQ $38 1440 MON.A1L .EQ $3C 1450 MON.A2L .EQ $3E 1460 MON.A4L .EQ $42 1470 SCM.POINTER .EQ $58 1480 SCM.CURR.CHAR .EQ $61 1490 SCM.ED.BEGLIN .EQ $80 1500 NEW.CH .EQ $98 1510 NEW.CV .EQ $99 1520 SCM.WBUF .EQ $200 1530 DOS.COLD.ENTRY .EQ $3D3 1540 DOS.IOHOOK .EQ $3EA 1550 FLAGS .EQ $7F8 VIDEX Flag Byte 1560 KEYBOARD .EQ $C000 1570 KEYSTROBE .EQ $C010 1580 SCM.WARM.ENTRY .EQ SCM.BASE+$003 1590 SCM.SHIFT.FLAG .EQ SCM.BASE+$016 1600 SCM.SYM.TABLE .EQ SCM.BASE+$01D 1610 SCM.TEST.DOS .EQ SCM.BASE+$31E 1620 SCM.RDL.EOL .EQ SCM.BASE+$35E 1630 SCM.RDL3 .EQ SCM.BASE+$3C3 1640 SCM.ESC.TABLE .EQ SCM.BASE+$467 1650 SCM.ESC.L .EQ SCM.BASE+$483 1660 SCM.RDKEY.NO.CASE .EQ SCM.BASE+$520 1670 SCM.RDKEY.WITH.CASE .EQ SCM.BASE+$4CA 1680 SCM.SPC .EQ SCM.BASE+$D92 1690 MON.MOVE .EQ $FE2C 1700 MON.OUTPORT .EQ $FE95 1710 MON.COUT .EQ $FDED 1720 MON.RTS .EQ $FF58 1730 *-------------------------------- 1740 .OR $4000 1750 START1 .EQ * 1760 *-------------------------------- 1770 MOVE.CODE 1780 LDA #HERE 1790 STA MON.A1L 1800 LDA /HERE 1810 STA MON.A1L+1 1820 LDA #THERE 1830 STA MON.A2L 1840 LDA /THERE 1850 STA MON.A2L+1 1860 *-------------------------------- 1870 .DO LCVERSION 1880 BIT $C083 Unprotect language card RAM 1890 BIT $C083 1900 LDA #LC.PATCH.AREA 1910 STA MON.A4L 1920 LDA /LC.PATCH.AREA 1930 STA MON.A4L+1 1940 .ELSE 1950 LDA #$33 Modify symbol table address 1960 STA SCM.SYM.TABLE 1970 LDA #PATCH.AREA 1980 STA MON.A4L 1990 LDA /PATCH.AREA 2000 STA MON.A4L+1 2010 .FIN 2020 *-------------------------------- 2030 LDY #0 2040 JSR MON.MOVE 2050 INSTALL.PATCHES 2060 LDA #$EA "NOP-OUT" unused code: 2070 STA SCM.BASE+$343 2080 STA SCM.BASE+$344 2090 STA SCM.BASE+$028 2100 STA SCM.BASE+$029 2110 STA SCM.BASE+$02A 2120 LDX #9 2130 .1 STA SCM.BASE+$298,X 2140 DEX 2150 BPL .1 2160 LDX #14 2170 .2 STA SCM.BASE+$4DE,X 2180 DEX 2190 BPL .2 2200 LDX #48 2210 .3 STA SCM.BASE+$B35,X 2220 DEX 2230 BPL .3 2240 LDA #$20 Install Videx during a 2250 STA SCM.BASE+$295 cold start 2260 LDA #INSTALL.VECTORS 2270 STA SCM.BASE+$296 2280 LDA /INSTALL.VECTORS 2290 STA SCM.BASE+$297 2300 LDA #HOME Patch clear screen routine 2310 STA SCM.BASE+$2A6 2320 LDA /HOME 2330 STA SCM.BASE+$2A7 2340 LDA #NEW.WARM.ENTRY Set up warm start so 2350 STA SCM.BASE+$309 VIDEX card stays in.. 2360 LDA /NEW.WARM.ENTRY 2370 STA SCM.BASE+$30A 2380 LDA #$10 Patch Escape Routine 2390 STA SCM.BASE+$486 2400 LDY #27 2410 .4 LDA NEW.ESC.TABLE,Y 2420 STA SCM.ESC.TABLE,Y 2430 DEY 2440 BPL .4 2450 LDA #$18 Modify MON.RDKEY jump addr 2460 STA SCM.BASE+$4D9 2470 LDA #$4C Patch jump to new DISP LINE 2480 STA SCM.BASE+$B32 2490 LDA #NEW.E.DISP.LINE 2500 STA SCM.BASE+$B33 2510 LDA /NEW.E.DISP.LINE 2520 STA SCM.BASE+$B34 2530 LDA #80 Patch E.INPUT Routine 2540 STA SCM.BASE+$CA8 2550 STA SCM.BASE+$CAC 2560 LDA #NEW.CH 2570 STA SCM.BASE+$CB1 2580 LDA #NEW.CV 2590 STA SCM.BASE+$CB3 2600 LDA #VTAB 2610 STA SCM.BASE+$CB5 2620 LDA /VTAB 2630 STA SCM.BASE+$CB6 2640 LDA #SLOTNUM Install VIDEX in hook 2650 JSR MON.OUTPORT 2660 JSR DOS.IOHOOK 2670 LDA #$8D Send CR to get VIDEX warm 2680 JSR MON.COUT entry point in DOS hook, 2690 LDY #8 then find warm entry address 2700 JSR SCM.TEST.DOS 2710 LDY #1 2720 LDA (SCM.POINTER),Y 2730 STA FAKE.COUT+1 Save warm entry as normal 2740 INY VIDEX COUT entry 2750 LDA (SCM.POINTER),Y 2760 STA FAKE.COUT+2 2770 LDA #COUT Hook in new I/O routines 2780 STA MON.CSW 2790 LDA /COUT 2800 STA MON.CSW+1 2810 LDA #RDKEY 2820 STA MON.KSW 2830 LDA /RDKEY 2840 STA MON.KSW+1 2850 JSR DOS.IOHOOK 2860 *-------------------------------- 2870 .DO LCVERSION 2880 BIT $C080 Write protect RAM 2890 JMP DOS.COLD.ENTRY 2900 .ELSE 2910 RTS 2920 .FIN 2930 *-------------------------------- 2940 * 2950 NEW.ESC.TABLE 2960 .DA HOME-1 2970 .DA ADVNCE-1 2980 .DA BS-1 2990 .DA LF-1 3000 .DA UP-1 3010 .DA CLREOL-1 3020 .DA CLREOP-1 3030 .DA MON.RTS-1 3040 .DA MON.RTS-1 3050 .DA UP-1 3060 .DA BS-1 3070 .DA ADVNCE-1 3080 .DA SCM.ESC.L-1 3090 .DA LF-1 3100 *-------------------------------- 3110 * New routines to bind into the 3120 * S-C Macro assembler 3130 *-------------------------------- 3140 LENGTH1 .EQ *-START1 3150 HERE .EQ * 3160 .DO LCVERSION 3170 .OR $F400 3180 .ELSE 3190 .OR $3200 3200 .FIN 3210 .TA HERE 3220 START2 .EQ * 3230 *-------------------------------- 3240 NEW.WARM.ENTRY 3250 JSR INSTALL.VECTORS 3260 JMP SCM.WARM.ENTRY 3270 * 3280 INSTALL.VECTORS 3290 LDA #COUT 3300 STA MON.CSW 3310 LDA /COUT 3320 STA MON.CSW+1 3330 LDA #RDKEY 3340 STA MON.KSW 3350 LDA /RDKEY 3360 STA MON.KSW+1 3370 JSR DOS.IOHOOK 3380 RTS 3390 * 3400 NEW.E.DISP.LINE 3410 LDA SCM.ED.BEGLIN 3420 STA NEW.CV 3430 LDA #0 3440 STA NEW.CH 3450 JSR VTAB 3460 JSR SCM.SPC 3470 INC NEW.CH 3480 INC NEW.CH 3490 LDX #0 3500 .1 LDA SCM.WBUF,X 3510 BEQ .5 3520 ORA #$80 3530 CMP #$A0 Control char? 3540 BCS .2 No.. 3550 AND #$7F Flag it as inverse 3560 .2 LDY NEW.CH 3570 CPY #80 End of screen line? 3580 BCC .4 No.. 3590 LDY #0 Set CH to beg of line 3600 STY NEW.CH 3610 LDY NEW.CV 3620 CPY #23 3630 BCS .3 3640 INC NEW.CV No.. 3650 BNE .4 ..Always 3660 .3 DEC SCM.ED.BEGLIN 3670 .4 JSR MON.COUT 3680 INC NEW.CH 3690 INX 3700 BNE .1 ..Always 3710 .5 JMP CLREOP 3720 * 3730 NEW.E.ZAP 3740 LDA #0 EOL mark 3750 STA SCM.WBUF,X 3760 JSR CLREOL 3770 RTS 3780 *-------------------------------- 3790 * Monitor Replacement Routines 3800 *-------------------------------- 3810 * 3820 HOME LDA #$8C Send Form Feed Char 3830 JMP MON.COUT 3840 * 3850 CLREOL LDA #$9D Send CLEAREOL char 3860 JMP MON.COUT 3870 * 3880 CLREOP LDA #$8B Send CLEAREOS char 3890 JMP MON.COUT 3900 * 3910 ADVNCE LDA #$9C Non-destructive space 3920 JMP MON.COUT 3930 * 3940 BS LDA #$88 Backspace 3950 JMP MON.COUT 3960 * 3970 LF LDA #$8A Linefeed 3980 JMP MON.COUT 3990 * 4000 UP LDA #$9F Reverse Linefeed 4010 JMP MON.COUT 4020 *-------------------------------- 4030 .DO LCVERSION 4040 RDKEY LDA KEYBOARD 4050 BPL RDKEY 4060 STA KEYSTROBE 4070 ORA #$80 4080 CMP #$81 Shift lock? 4090 BNE .1 4100 JSR UNPROTECT.LC.RAM 4110 LSR SCM.SHIFT.FLAG 4120 BPL .2 Return with errant key 4130 .1 CMP #$9A Shift unlock? 4140 BNE .3 No, return with key 4150 JSR UNPROTECT.LC.RAM 4160 SEC 4170 ROR SCM.SHIFT.FLAG 4180 .2 BIT $C080 Reprotect LC RAM 4190 LDA #$96 Return with errant key 4200 .3 RTS 4210 * 4220 UNPROTECT.LC.RAM 4230 BIT $C083 Enable Bank 2 4240 BIT $C083 4250 RTS 4260 .ELSE 4270 RDKEY LDA KEYBOARD 4280 BPL RDKEY 4290 STA KEYSTROBE 4300 ORA #$80 4310 CMP #$81 Shift lock? 4320 BNE .1 4330 LSR SCM.SHIFT.FLAG 4340 BPL .2 Return with errant key 4350 .1 CMP #$9A Shift unlock? 4360 BNE .3 No, return with key 4370 SEC 4380 ROR SCM.SHIFT.FLAG 4390 .2 LDA #$96 Return with errant key 4400 .3 RTS 4410 .FIN 4420 *-------------------------------- 4430 * 4440 VTAB LDA #$9E Send GOTOXY char 4450 JSR MON.COUT 4460 CLC Create ASCII x-posn 4470 LDA NEW.CH 4480 ADC #160 4490 JSR MON.COUT 4500 CLC Create ASCII y-posn 4510 LDA NEW.CV 4520 ADC #160 4530 JMP MON.COUT 4540 * 4550 COUT 4560 PHA Test for inverse 4570 PLA 4580 BMI FAKE.COUT Not inverse: Take as is 4590 ORA #$80 Restore to "Normal" Apple ASCII 4600 CMP #$A0 Control char? 4610 BCS .1 No.. 4620 ORA #$40 Yes: Make it printable 4630 .1 TAY Save char 4640 LDA FLAGS+SLOTNUM 4650 PHA Save flag byte 4660 ORA #1 Switch in alt char set 4670 STA FLAGS+SLOTNUM 4680 TYA Get char back 4690 JSR FAKE.COUT 4700 PLA Restore flag byte 4710 STA FLAGS+SLOTNUM 4720 RTS 4730 FAKE.COUT 4740 JMP $FFFF Address will be fixed later.. 4750 *-------------------------------- 4760 LENGTH2 .EQ *-START2 4770 THERE .EQ HERE+LENGTH2-1 4780 LENGTH .EQ LENGTH1+LENGTH2 4790 *-------------------------------- 4800 .EN |
If you are at all interested in Apple graphics, or writing animated hi-res games, this book is for you. Jeffrey Stanton, the author, may already be known to you. He is the editor of "The Book of Apple Software, and also has several Apple arcade games on the market. "Apple Graphics & Arcade Game Design" (AGAG) is 288 pages long, and retails for $19.95. (I am selling it for $18 plus shipping.) A coupon in the back enables you to purchase all of the source code shown in the book on diskette for only $15.
There are two parts to the book: first, a thorough explanation of Apple graphics, with numerous examples in both Applesoft and assembly language; second, design and programming of all the parts of a working arcade game.
AGAG is written for the advanced Applesoft or beginning assembly language programmer. You learn about both lo-res and hi-res graphics at the assembly language level. You learn the fundamentals, and then proceed to program scene scrolling, page flipping, laser fire, bomb drops, explosions, scoring, and paddle control routines. Sorry, nothing much about sound generation.
AGAG's pages are divided into 8 chapters as follows:
1. ( 25 pages) Applesoft Hi-Res
2. ( 34 pages) Lo-Res Graphics
3. ( 17 pages) Machine Language Access to Applesoft
Hi-Res Routines
4. ( 23 pages) Hi-Res Screen Architecture
5. ( 36 pages) Bit-Mapped Graphics
6. ( 90 pages) Arcade Graphics
7. ( 44 pages) Games that Scroll
8. ( 5 pages) What Makes a Good Game
I noticed a few errors in the book: on page 149, flow chart lines are incorrectly drawn; on page 284, there is a large block of repeated text, and therefore possibly a missing block which should have been in the space. The word "initialize" is always incorrectly spelled "initilize". The index is very brief, only about 70 lines long; I believe it should be about 3 or 4 times longer to really help in locating items of interest.
Jeff does not seem to know about the existence of the S-C Macro Assembler. He repeatedly mentions the TED, Big-Mac, Merlin Assemblers, and occasionally refers to Lisa and DOS ToolKit. All the listings are in the Big-Mac format. You should have no trouble adapting them to the S-C format.
AGAG is an excellent tutorial, and includes many useful programs and ideas for anyone interested in Apple graphics. I heartily recommend the book, ranking it just under "Beneath Apple DOS" in importance and utility.
I just received the July AAL and liked the little article on the "FILEDUMP" command. I had already done just about the same thing.
In fact, I make a lot of changes to DOS. Too many to POKE in every time I boot up. So I started looking around for a simple way to replace the DOS image on a disk without disturbing the programs already on it, and without using MASTER.CREATE. The July Call A.P.P.L.E. had a program to do it, only it seems much more complicated than my solution.
I used the S-C Macro Assembler to create a text file like this:
:1000 LOAD HELLO
:1010 POKE -21921,0:POKE -18448,0:POKE
-18447,157:POKE-18453,0:CALL-18614
:TEXT WRITE.DOS
Note the leading blank before the LOAD and the first POKE. It is there to leave room for Applesoft's "]" prompt.
Whenever I want to write the DOS image on a disk, I use the SHOW command to list out WRITE.DOS, and then trace over the two command lines from Applesoft. Presto-Changeo, a new copy of DOS goes out to the disk. I suppose you could even EXEC it, though I prefer to trace over it and haven't tried EXECing.
The LOAD HELLO is there to get the boot file name into DOS's filename buffer. You can use whatever filename you want, of course. POKE-21921 tell DOS that the last command was an INIT for its startup procedure (i.e. AA5F:00). POKE-18448 and -18447 start the write at 9D00 (B7F0:00 9D). POKR -18453 sets the expected volume number to zero, so a match to any volume will occur (B7EB:00). The CALL is to the "write DOS image" code inside DOS.
Last month I described the BIT instruction incorrectly. The next to the last paragraph on page 2 (in "Run-Anywhere Subroutine Calls") should read:
The BIT instruction copies bit 7 of $FF58 into the N-status bit, and bit 6 into the Overflow status bit. This, in other words (since $FF58 has $60 in it) clears N and sets Overflow.
BIT does not affect Carry Status in any way. BIT also sets or clears the Z-status bit, according to the value of the logical product of the A-register and the addressed byte. If you want Z and/or N to be flags to the calling program, you will have to modify them after the BIT instruction.
One of the more common questions we get is: "How do I best use the .IN and .TF directives to handle very large programs?"
The main technique we use is the Assembly Control File (ACF), a short source file which is mostly made up of .IN statements to call the other modules. Here is an example, called SAMPLE.ACF:
1000 .IN SAMPLE.EQUATES
1010 .PG
1020 .IN SAMPLE.CODE.1
1030 .PG
1040 .IN SAMPLE.CODE.2
1050 .PG
1060 .IN SAMPLE.DATA
1070 .PG
|
SAMPLE.EQUATES is all the definitions for the program, SAMPLE.CODE.1 and SAMPLE.CODE.2 are the main body of the program, and SAMPLE.DATA contains all the variables and ASCII text. When you want to assemble the program, just LOAD SAMPLE.ACF and type MON C then ASM. The Macro Assembler will load each file and assemble it, in the order they are listed in the ACF. The "MON C" shows you the "LOAD file name" for each file, helping you to tell what's where.
Using this technique, a program can conveniently be broken into as many modules as you want, and can be as large as you want. The Macro Assembler itself is 26 source files on two disks! To spread the files across more than one disk, just add drive (and/or slot) specifiers to all the file names.
You can also use the ACF to do global search-and-replace operations on the entire program. Here are the commands to search SAMPLE for all occurrences of the label MON.COUT:
:LOAD SAMPLE.ACF
:REP / .IN/LOAD/A
:REP / .PG/FIND "MON.COUT"/A
:TEXT COUT.SEARCH
:MON I
:EXEC COUT.SEARCH
|
This converts SAMPLE.ACF into an EXEC file that will list each occurrence of "MON.COUT" in every module of the program. Here's what the file looks like now:
1000 LOAD SAMPLE.EQUATES
1010 FIND "MON.COUT"
1020 LOAD SAMPLE.CODE.1
1030 FIND "MON.COUT"
1040 LOAD SAMPLE.CODE.2
1050 FIND "MON.COUT"
1060 LOAD SAMPLE.DATA
1070 FIND "MON.COUT"
|
The ACF is also a good place for the .OR and .TF statements, comments about the assembly process, and any condition flags. Here is a more complicated version of SAMPLE.ACF:
1000 *--------------------------------
1010 * SAMPLE FILE TO DEMONSTRATE ACF
1020 *--------------------------------
1030 LC.FLAG .EQ 0 =0 IF UPPER CASE ONLY
1040 * =1 IF LOWER CASE VERSION
1050 *--------------------------------
1060 .OR $803
1070 .DO LC.FLAG
1080 .TF B.SAMPLE.LC
1090 .ELSE
1100 .TF B.SAMPLE.UC
1110 .FIN
1120 *--------------------------------
1130 .IN SAMPLE.EQUATES
1140 .PG
1150 .IN SAMPLE.CODE
1160 .PG
1170 .DO LC.FLAG
1180 .IN SAMPLE.LOWER.CASE.ROUTINES
1190 .PG
1200 .ELSE
1210 .IN SAMPLE.NORMAL.ROUTINES
1220 .PG
1230 .FIN
1240 .IN SAMPLE.DATA
1250 .PG
|
To use this ACF, just LOAD it, EDIT line 1030 to set LC.FLAG to 0 or 1, set MON C, and ASM. The Macro Assembler will load the appropriate source files for the version you want and direct the object code to the correct target file. To turn this ACF into an EXEC file for searching, you must delete lines 1000-1120, 1170, 1200, and 1230 before doing the REP commands.
For more information on the .IN and .TF directives, see pages 4-6 and 5-3/4 in the Macro Assembler manual. Conditional assembly is discussed on pages 5-9/10 and in chapter 7.
Version 4.0 of the S-C Assembler stopped after any assembly error. Many users requested that I modify it to continue to the end of assembly, and display the error count at the end. So I did.
Now some users are requesting that I change it back. They walk away during assembly, and the error messages scroll off the screen. (But you can put .LIST OFF at the beginning, and then only the error lines will list.)
There is a very simple patch for this. The byte at $1D6F ($DD6F in the language card version) is now $18. Change it $38 and assembly will stop after the first error message.
When I added the lower-case options to the S-C Macro Assembler, I overlooked the fact that within .AS and .AT strings, and in ASCII literal constants, you would want lower case codes to be assembled. The assembler as it now is converts all lower case codes to upper case during assembly. For example, ".AS /Example/" would assemble all upper case ASCII, just as though you had written ".AS /EXAMPLE/"
The following patches will correct this problem, allowing you to specify lower case strings and constants when you wish.
$2961:EA EA EA EA EA EA
$31B8<1235.124BM
$1074:B8 31
$118C:B8 31
$11B2:B8 31
$187F:B8 31
$23FA:B8 31
$31CF:C8 84 7B C9 60 90 04 29 5F 85 61 60
$1240:20 CF 31
BSAVE ASM.WITH.LC.IN.AS,A$1000,L$21DB
(or whatever file name you wish)
The patches above are for the version which runs in mother-board RAM. The Language card version has different addresses, and you must first write-enable the language card. Assuming you are currently running the language card version, perform the patch as follows:
$C083 C083
$EAAD:EA EA EA EA EA EA
$F304<D235.D24BM
$D074:04 F3
$D18C:04 F3
$D1B2:04 F3
$D87F:04 F3
$E546:04 F3
$F31B:C8 84 7B C9 60 90 04 29 5F 85 61 60
$D240:20 1B F3
BSAVE LC.ASM.WITH.LC.IN.AS,A$D000,L$2327
(or whatever file name you wish)
Be aware that the above patches may conflict with other patches you may already have applied to your copy of the assembler. If you have already used the area from $31B8 through $31DB, or $F304 through $F326, you will need to use a different area and change the references accordingly.
Early users of the ES-CAPE Applesoft Editing system (formerly known as AED II) have really come to appreciate the blinking underline cursor -- it simply doesn't tire the eyes as much as the standard flashing blank does. With the following subroutine, you can add this special touch to your own assembly language or BASIC programs!
The subroutine hooks into the monitor keyboard input vector at $38 and $39. Each time the monitor RDKEY subroutine is called, my KEYIN subroutine gets control. If the character on the screen at the cursor position is not an underline, I alternate the display of an underline and the original character every 1/4 second. If the original character was an underline, I alternate it with a blank. (If I alternate an underline with an underline, it is difficult to see anything happen!)
Lines 1210-1250 store the KEYIN subroutine's address in the keyboard input vector. When a request for a key press is made by an Applesoft INPUT command, for example, we get control at line 1270. The A-register has the current screen character. I save the A- and X-registers, because KEYIN must exit with the original values unchanged.
Lines 1290-1320 test the current screen character to see whether it is already an underline or not. If it is, I use a blank for the alternating character. Otherwise, I use the original screen contents for an alternating character. I push the alternating character onto the stack.
Lines 1330-1500 do the alternating. I look at the character on the screen: if it is an underline, I substitute the alternating character; if not, I store an underline. The lines 1430-1500 delay for about 1/4 second before the next alternation. If a keypress occurs, the loop ends by branching to ".5" at line 1540. You may wish to vary the blink rate by changing the value loaded into the Y-register at line 1430.
When a key is pressed we end up at line 1540, where I pop the alternating character off the stack. The I call the monitor bell subroutine for a short (10 half-cycles) bell. This makes an audible "click" for user feedback. (If you don't appreciate clicking keyboards, just delete lines 1550 and 1560.) Then I restore the Y-, X-, and A-registers to their original values, and jump into the monitor's KEYIN subroutine at $FD26. The monitor restores the original character to the screen, and returns with the keypress value in the accumulator.
I have set the subroutine origin to $300, but you can assemble it anywhere you like. In fact, it will run anywhere you put without reassembly, just so you load the correct address into $38 and $39 in the HOOK routine.
After assembly, assuming it is origined at $300, you can BSAVE it with "BSAVE B.UNDERLINE,A$300,L$3C. Then to activate this routine from Applesoft, just BRUN the file B.UNDERLINE. All keyboard input through the standard monitor RDKEY subroutine ($FDOC) or Applesoft GET and INPUT statements will be prompted by the underline cursor. An "IN#0" will restore the familiar flashing blank. Have fun!
1000 *SAVE S.UNDERLINE CURSOR 1010 *-------------------------------- 1020 * BLINKING UNDERLINE CURSOR 1030 * WRITTEN BY BILL LINN 1040 *-------------------------------- 1050 .OR $300 1060 *-------------------------------- 1070 MON.CH .EQ $24 1080 MON.BASL .EQ $28 1090 MON.KSWL .EQ $38 1100 MON.RNDL .EQ $4E 1110 *-------------------------------- 1120 DOS.REHOOK .EQ $3EA 1130 *-------------------------------- 1140 MON.BELL2 .EQ $FBE4 1150 MON.WAIT .EQ $FCA8 1160 MON.KEYIN3 .EQ $FD26 1170 *-------------------------------- 1180 BLANK .EQ $A0 1190 UNDERLINE .EQ $DF 1200 *-------------------------------- 1210 KEYBOARD .EQ $C000 1220 *-------------------------------- 1230 HOOK LDA #KEYIN SET INPUT HOOK 1240 STA MON.KSWL 1250 LDA /KEYIN 1260 STA MON.KSWL+1 1270 JMP DOS.REHOOK 1280 *-------------------------------- 1290 KEYIN PHA SAVE SCREEN CHAR 1300 STX MON.RNDL SAVE X-REG 1310 CMP #UNDERLINE IF CHAR ON SCREEN IS 1320 BNE .1 AN UNDERLINE 1330 LDA #BLANK THEN ALTERNATE WITH BLANK 1340 .1 PHA SAVE CHAR TO ALTERNATE 1350 *-------------------------------- 1360 * ALTERNATE UNTIL KEY IS PRESSED 1370 *-------------------------------- 1380 .2 LDA #UNDERLINE 1390 LDY MON.CH 1400 CMP (MON.BASL),Y 1410 BNE .3 1420 PLA GET ALTERNATE CHAR 1430 PHA MAINTAIN ON STACK ALSO 1440 .3 STA (MON.BASL),Y 1450 LDY #80 80*256 BETWEEN BLINKS 1460 .4 LDA KEYBOARD KEY PRESSED? 1470 BMI .5 YES, CLICK AND RETURN 1480 DEX 1490 BNE .4 1500 DEY 1510 BNE .4 1520 BEQ .2 ...ALWAYS 1530 *-------------------------------- 1540 * A KEY HAS BEEN PRESSED 1550 *-------------------------------- 1560 .5 PLA POP STACK ONCE 1570 LDY #10 MAKE A "CLICK" 1580 JSR MON.BELL2 1590 LDY MON.CH 1600 LDX MON.RNDL RESTORE X-REG 1610 PLA RESTORE ORIGINAL SCREEN CHAR 1620 JMP MON.KEYIN3 |
I had already started writing my own debugger when I discovered QUICKTRACE; it was just what I needed and saved me all that work.
It has a good display that does not interfere with the normal Apple text screen. You can even trace code that sets the KSWL and CSWL switches and outputs to the screen. The tracing display takes the bottom four lines, but pressing the "P" key causes the normal bottom four lines to be displayed.
Tracing can be in one of three modes: single-step, trace, and background. Single-step and trace are what you would expect, analogous to the commands in the old Apple monitor ROM. Background turns off the display of executed instructions until a breakpoint occurs or the "ESC" key is pressed. This makes background the fastest mode.
Breakpoints can be set to stop when:
QUICKTRACE can be BRUN at any point in memory and then called from your code by a JSR, or you can preset the QUICKTRACE program counter and start tracing at any location.
Subroutines can be executed at full 6502 speed (not traced). If you already know what the subroutine does there is no need to trace through it. Normally DOS calls are automatically done this way to prevent timing problems.
Overall I feel that QUICKTRACE is one of the five or so best programs I have ever purchased and no machine code programmer should be without it.
One feature not to be overlooked: QUICKTRACE is not copy protected.
QUICKTRACE was programmed by John Rogers and it is distributed by Anthro-Digital Software (formerly called Aurora Systems). It only costs $50.
Current Advertising Rates
For the September 1982 issue the price will be $60 for a full page, $35 for a half page. To be included, I must receive your camera-ready copy by August 20th.