Over the years I have shared many tidbits about Color BASIC.
This is another one.
A recent post by Juan Castro to the Groups.IO Color Computer mailing list caught my attention, mostly because he called me out by name in the subject line:
As a reminder, Color BASIC allows 1 or 2 character variable names. They must start with a letter (A-Z) and the second character can be either letter (A-Z) or number (A-0). BUT, the BASIC interpreter does let you type longer names for variables, but it only honors the first two characters. Here is a screenshot from a past blog post here (which I’d link to if I was not so lazy):
Color BASIC variables may be very long, but only the first two characters are used.
This is a reminder that, if you try to use variables longer than two characters, you have to make sure you always keep the first two characters unique since “LONGVARIABLE” and “LOST” and “LO” are all the same variable to BASIC.
…but not all variable name limits are the same.
To break the rule I just said, in Color BASIC, some variable names are forbidden. A forbidden variable is one you cannot use because it is already reserved for a keyword or token. For example, FOR is a keyword:roar
FOR I=1 TO 10 PRINT I NEXT I
Because of this, even though BASIC only honors the first two characters of a variable name, you still cannot use “FOR” as a variable.
FOR=42 ?SN ERROR
But you can use “FO”, since that is not long enough to be recognized as a BASIC token or keyword.
FO=42 PRINT FO 42
There are a number of two-character tokens, such as “TO” in the FOR/NEXT statement (“FOR I=1 TO 10”), and “AS” in the Disk BASIC FIELD statement (“FIELD #1,5 AS A$”), as well as “FN” which is used in DEF FN.
AS=42 ?SN ERROR
FN=42 ?SN ERROR
TO=42 ?SN ERROR
This means if you wrote something for Color BASIC or Extended Color BASIC that uses “AS” as a variable, that would not work under Disk Extended Color BASIC.
BASIC ignores spaces
In recent years, someone pointed me to the fact that when scanning a BASIC line (either type in directly or when parsing a line of code in a program), spaces get ignored by the scanner. This means:
N M = 42 PRINT N M 42
That one surprised me when I learned it. This is probably why, when printing two variables, a semicolon is required between them:
N = 10 M = 20 PRINT N;M 10 20
And if you had done this (remember to CLEAR between these tests so variables are erased each time):
N = 10 M = 20 NM = 30 PRINT N M 30 PRINT N;M;N M 10 20 30
By the way, if you have ever wondered about that space printed in front of numeric variables when you do things like “PRINT X”, I covered why this happens in an earlier blog and included a simple patch to BASIC that removes that feature.
How to turn a forbidden variable into a non-forbidden one for fun and profit
Well, Juan Casto showed that using this “BASIC ignores spaces” quirk as a way to use forbidden variables. From his post:
Now it seems obvious. BASIC’s interpreter looks for keywords like “FOR” and will not recognize “F O R” or “FO R” as that token. The detokenizer honors the spaces.
But when it comes to variables, the spaces are ignored by the parser, so “T O” will not match as a token for “TO”, but will be processed as a variable “TO”.
Go figure.
Admittedly, space in two-character variable names look silly, but now I can finally update my old *ALLRAM* BBS to use the variable “TO$” for who a message is to:
FR$="ALLEN HUFFMAN" T O$="JUAN CASTRO" SB$="THAT'S REALLY COOL"
I suspect this was discovered by the early pioneers of BASIC, likely soon after the original Color Computer was released in 1980. If you know of a reference to this behavior from some early newsletter or magazine article, please let me know.
And as to Juan … thanks for sending me down a BASIC rabbit hole again…
Just when I thought I was out, they pull me back in.
In part 3 I showed a simple assembly language routine that would uppercase a string.
In part 5, this routine was made more better by contributions from commenters.
Today, I revisit this code and update it to use “what I now know” (thank you, Sean Conner) about being able to pass strings into a USR function without using VARPTR.
First, here is the code from part 5:
* UCASE.ASM v1.01 * by Allen C. Huffman of Sub-Etha Software * www.subethasoftware.com / alsplace@pobox.com * * 1.01 a bit smaller per Simon Jonassen * * DEFUSRx() uppercase output function * * INPUT: VARPTR of a string * RETURNS: # chars processed * * EXAMPLE: * CLEAR 200,&H3F00 * DEFUSR0=&H3F00 * A$="Print this in uppercase." * PRINT A$ * A=USR0(VARPTR(A$)) * ORGADDR EQU $3f00
opt 6809 * 6809 instructions only opt cd * cycle counting
org ORGADDR
start jsr INTCNV * get passed in value in D tfr d,x * move value (varptr) to X ldy 2,x * load string addr to Y beq null * exit if strlen is 0 ldb ,x * load string len to B ldx #0 * clear X (count of chars conv)
loop lda ,y+ * get next char, inc Y ; lda ,y * load char in A cmpa #'a * compare to lowercase A blt nextch * if less, no conv needed cmpa #'z * compare to lowercase Z bgt nextch * if greater, no conv needed lcase suba #32 * subtract 32 to make uppercase leax 1,x * inc count of chars converted nextch jsr [CHROUT] * call ROM output character routine ; leay 1,y * increment Y pointer cont decb * decrement counter bne loop * not done yet ; beq exit * if 0, go to exit ; bra loop * go to loop
exit tfr x,d * move chars conv count to D jmp GIVABF * return to caller
null ldd #-1 * load -2 as error return jmp GIVABF * return to caller
In the header comment you can see an example of the usage, and that it involved using VARPTR on a string to get the string’s descriptor location in memory, then pass that address into the USR function.
Now that I know we can just pass a string in directly, I thought it would be fun (?) to update this old code to use that method. Here is what I came up with. Note that I changed the “*” comments to “;” since the a09 assembly does not support those. If you wanted to run this in EDTASM, you would have to change those back.
; UCASE3.ASM v1.02 ; by Allen C. Huffman of Sub-Etha Software ; www.subethasoftware.com / alsplace@pobox.com ; ; 1.01 a bit smaller per Simon Jonassen ; 1.02 converted to allow passing a string in to USR ; ; DEFUSRx() uppercase output function ; ; INPUT: string ; RETURNS: # chars converted or -1 if error ; ; EXAMPLE: ; CLEAR 200,&H3F00 ; DEFUSR0=&H3F00 ; A$="Print this in uppercase." ; PRINT A$ ; A=USR0(A$) ; PRINT "CHARS CONVERTED:";A ; A=USR0("This is another test"); ; PRINT "CHARS CONVERTED:";A ; ORGADDR EQU $3f00
start jsr CHKSTR ; ?TM ERROR if not a string. ; X will be VARPTR, B will be string length tstb beq reterror ; exit if strlen is 0 ldy 2,x ; load string addr to Y ldx #0 ; clear X (count of chars conv)
loop lda ,y+ ; get next char, inc Y cmpa #'a ; compare to lowercase A blo nextch ; if less, no conv needed cmpa #'z ; compare to lowercase Z bhi nextch ; if greater, no conv needed suba #32 ; subtract 32 to make uppercase leax 1,x ; inc count of chars converted nextch jsr [CHROUT] ; call ROM output character routine decb ; decrement counter bne loop ; not done yet
tfr x,d ; move chars conv count to D bra return
reterror ldd #-1 ; load -1 as error return jmp GIVABF ; return to caller
Here are the changes… In the original version, I have this:
start jsr INTCNV * get passed in value in D tfr d,x * move value (varptr) to X ldy 2,x * load string addr to Y beq null * exit if strlen is 0 ldb ,x * load string len to B ldx #0 * clear X (count of chars conv)
That first jsr INTCNV expects a number parameter and, if not a number, it exits with ?TM ERROR. If it gets past that, the number is in the D register and it gets transferred over to X. In this case, the number is the value returned by VARPTR:
A=USR0(VARPTR(A$))
That value is the address of the 5-byte string descriptor that contains the address of the actual string data and the length of that data. Y is loaded with 2 bytes in from wherever X points which makes Y contain the address of the string data.
After this is a bug, I think. Looking at the comments, I think that “beq null” should be one line lower, like this:
start jsr INTCNV * get passed in value in D tfr d,x * move value (varptr) to X ldy 2,x * load string addr to Y ldb ,x * load string len to B beq null * exit if strlen is 0 ldx #0 * clear X (count of chars conv)
That way, Y is loaded with the address of the string data, then b is loaded with the length of that data, and the branch-if-equal check is now checking B. If the length is 0, it is an empty string so no processing can be done on it. (That’s a bug, right?)
The new code is this:
start jsr CHKSTR ; ?TM ERROR if not a string. ; X will be VARPTR, B will be string length tstb beq reterror ; exit if strlen is 0 ldy 2,x ; load string addr to Y ldx #0 ; clear X (count of chars conv)
The first line is something I learned from Sean Conner‘s excellent writeup on USR. That is an undocumented ROM call which checks is a variable is a string. If it isn’t, it will return back to BASIC with a ?TM ERROR. By having that check there, if the user tries to pass in a number, that error will be seen. As a bonus, if you try to EXEC that code, that, too, will show ?TM ERROR.
After that, B should be the length of the string so tstb checks that to be 0 (empty string) then the rest of the code is similar.
As I write this, I could have altered the order of my new code to do the tstb/beq after the ldy and then it would be closer to how the original worked. But since the original appears buggy, I won’t worry about that.
Now if I load this and set it up, I should see this:
DEF USR0=&H3F00
A=USR0(42) ?TM ERROR
A=USR0("This is a test") THIS IS A TEST
Also, I notice that the value I return can be -1 if you pass in an empty string…
A=USR0("") OK PRINT A -1
…and if it is non-empty, it is only the count of the characters that had to be converted. So “Hello World” converts the “ello” and “orld” for a return value of 8. It does not touch the uppercase “H” and “W” or the space.
I am not sure that is really useful. The code could be modified to return the length of the string it processed, but at least this way you know that a positive non-zero return value means it did do some work.
What do you use your computer for? [_] Word Processing [_] Businesss [_] Games/Fun [_] Telecom [_] Programming [_] Home Apps. [_] Music/MIDI [_] Graphics
I wrote a BASIC program which will create 68 files named “0.TXT” to “67.TXT”. Each file is 2304 bytes so it takes up a full granule. (That is not really important. It just helps makes things obvious if you look at the disk with a hex editor and want to know which file is at which sector.)
After making these files, it uses code from some of my other examples to scan through the directory and display it (FILEGRAN.BAS code, shown later in this post) and then it scans the directory and prints which granule each 1-gran file is using.
I can start with a freshly formatted disk then run this program and see where RS-DOS put each file.
Will it match the order RS-DOS used when making one huge file that takes up all 68 grans? Let’s find out…
10 '68FILES.BAS 20 PRINT "RUN THIS ON A BLANK DISK." 30 INPUT "DRIVE #";DR 40 'SWITCH TO THAT DRIVE 50 DRIVE DR 60 'GOTO 140 70 'MAKE FILES 0-67 80 FOR G=0 TO 67 90 F$=MID$(STR$(G),2)+".TXT" 100 PRINT "MAKING ";F$; 110 OPEN "O",#1,F$ 120 CLOSE #1:PRINT 130 NEXT 140 'FILEGRAN.BAS 150 'DIR WITHOUT FILE SIZES 160 CLEAR 512:DIM SP$(1) 170 ' S - SECTOR NUMBER 180 FOR S=3 TO 11 190 ' SP$(0-1) - SECTOR PARTS 200 DSKI$ DR,17,S,SP$(0),SP$(1) 210 ' P - PART OF SECTOR 220 FOR P=0 TO 1 230 ' E - DIR ENTRY (4 P/SECT.) 240 FOR E=0 TO 3 250 ' GET 32 BYTE DIR ENTRY 260 DE$=MID$(SP$(P),1+E*32,32) 270 ' FB - FIRST BYTE OF NAME 280 FB=ASC(LEFT$(DE$,1)) 290 ' SKIP DELETED FILES 300 IF FB=0 THEN 440 310 ' WHEN 255, DIR IS DONE 320 IF FB=255 THEN 470 330 ' PRINT NAME AND EXT. 340 'PRINT LEFT$(DE$,8);TAB(9);MID$(DE$,9,3); 350 ' FIRST TWO CHARS ONLY 360 PRINT LEFT$(DE$,2);"-"; 361 'PRINT #-2,LEFT$(DE$,2);","; 370 ' FILE TYPE 380 'PRINT TAB(13);ASC(MID$(DE$,12,1)); 390 ' BINARY OR ASCII 400 'IF ASC(MID$(DE$,13,1))=0 THEN PRINT "B"; ELSE PRINT "A"; 410 ' STARTING GRANULE 420 PRINT USING("## ");ASC(MID$(DE$,14,1)); 421 'PRINT #-2,ASC(MID$(DE$,14,1)) 430 CL=CL+1:IF CL=5 THEN CL=0:PRINT 440 NEXT 450 NEXT 460 NEXT 470 END
I modified this program to output to the printer (PRINT #-2) and then capture that output in the Xroar emulator in a text file. That gave me data which I put in a spreadsheet.
Next, I used a second program on a freshly formatted disk to create one big file fully filling up the disk. (The very last PRINT to the file will create a ?DF ERROR, which I now think is a bug. It should not do that until I try to write the next byte, I think.)
10 '1BIGFILE.BAS 20 PRINT"RUN THIS ON A BLANK DISK." 30 INPUT "DRIVE #";DR 40 'SWITCH TO THAT DRIVE 50 DRIVE DR 60 'MAKE ONE BIG 68 GRAN FILE 70 OPEN "O",#1,"1BIGFILE.TXT" 80 FOR G=0 TO 67 90 PRINT G; 100 T$=STRING$(128,G) 110 FOR T=1 TO 18 120 PRINT "."; 130 PRINT #1,T$; 140 NEXT 150 PRINT 160 NEXT 170 CLOSE #1 180 END
I ran another test program which would read the directory, then print out the granule chain of each file on the disk.
10 ' FILEGRAN.BAS 20 ' 30 ' 0.0 2025-11-20 BASED ON FILEINFO.BAS 40 ' 50 ' E$(0-1) - SECTOR HALVES 60 ' FT$ - FILE TYPE STRINGS 70 ' 80 CLEAR 1500:DIM E$(1),FT$(3) 90 FT$(0)="BPRG":FT$(1)="BDAT":FT$(2)="M/L ":FT$(3)="TEXT " 100 ' 110 ' DIR HOLDS UP TO 72 ENTRIES 120 ' 130 ' NM$ - NAME 140 ' EX$ - EXTENSION 150 ' FT - FILE TYPE (0-3) 160 ' AF - ASCII FLAG (0/255) 170 ' FG - FIRST GRANULE # 180 ' BU - BYTES USED IN LAST SECTOR 190 ' SZ - FILE SIZE 200 ' GM - GRANULE MAP 210 ' 220 DIM NM$(71),EX$(71),FT(71),AF(71),FG(71),BU(71),SZ(71),GM(67) 230 ' 240 INPUT "DRIVE";DR 250 ' 260 ' FILE ALLOCATION TABLE 270 ' 68 GRANULE ENTRIES 280 ' 290 DIM FA(67) 300 DSKI$ DR,17,2,G$,Z$:Z$="" 310 FOR G=0 TO 67 320 FA(G)=ASC(MID$(G$,G+1,1)) 330 NEXT 340 ' 350 ' READ DIRECTORY 360 ' 370 DE=0 380 FOR S=3 TO 11 390 DSKI$ DR,17,S,E$(0),E$(1) 400 ' 410 ' PART OF SECTOR 420 ' 430 FOR P=0 TO 1 440 ' 450 ' ENTRY WITHIN SECTOR PART 460 ' 470 FOR E=0 TO 3 480 ' 490 ' DIR ENTRY IS 32 BYTES 500 ' 510 E$=MID$(E$(P),E*32+1,32) 520 ' 530 ' NAME IS FIRST 8 BYTES 540 ' 550 NM$(DE)=LEFT$(E$,8) 560 ' 570 ' EXTENSION IS BYTES 9-11 580 ' 590 EX$(DE)=MID$(E$,9,3) 600 ' 610 ' FILE TYPE IS BYTE 12 620 ' 630 FT(DE)=ASC(MID$(E$,12,1)) 640 ' 650 ' ASCII FLAG IS BYTE 13 660 ' 670 AF(DE)=ASC(MID$(E$,13,1)) 680 ' 690 ' FIRST GRANUAL IS BYTE 14 700 ' 710 FG(DE)=ASC(MID$(E$,14,1)) 720 ' 730 ' BYTES USED IN LAST SECTOR 740 ' ARE IN BYTES 15-16 750 ' 760 BU(DE)=ASC(MID$(E$,15,1))*256+ASC(MID$(E$,16,1)) 770 ' 780 ' IF FIRST BYTE IS 255, END 790 ' OF USED DIR ENTRIES 800 ' 810 IF LEFT$(NM$(DE),1)=CHR$(255) THEN 1500 820 ' 830 ' IF FIRST BYTE IS 0, FILE 840 ' WAS DELETED 850 ' 860 IF LEFT$(NM$(DE),1)=CHR$(0) THEN 1480 870 ' 880 ' SHOW DIRECTORY ENTRY 890 ' 900 PRINT NM$(DE);TAB(9);EX$(DE);" ";FT$(FT(DE));" "; 910 IF AF(DE)=0 THEN PRINT"BIN"; ELSE PRINT "ASC"; 920 ' 930 ' CALCULATE FILE SIZE 940 ' SZ - TEMP SIZE 950 ' GN - TEMP GRANULE NUM 960 ' SG - SECTORS IN LAST GRAN 970 ' GC - GRANULE COUNT 980 ' 990 SZ=0:GN=FG(DE):SG=0:GC=0 1000 ' 1010 ' GET GRANULE VALUE 1020 ' GV - GRAN VALUE 1030 ' 1040 GV=FA(GN):GM(GC)=GN:GC=GC+1 1050 ' 1060 ' IF TOP TWO BITS SET (C0 1070 ' OR GREATER), IT IS THE 1080 ' LAST GRANULE OF THE FILE 1090 ' SG - SECTORS IN GRANULE 1100 ' 1110 IF GV>=&HC0 THEN SG=(GV AND &H1F):GOTO 1280 1120 ' 1130 ' IF NOT, MORE GRANS 1140 ' ADD GRANULE SIZE 1150 ' 1160 SZ=SZ+2304 1170 ' 1180 ' MOVE ON TO NEXT GRANULE 1190 ' 1200 GN=GV 1210 GOTO 1040 1220 ' 1230 ' DONE WITH GRANS 1240 ' CALCULATE SIZE 1250 ' 1260 ' FOR EMPTY FILES 1270 ' 1280 IF SG>0 THEN SG=SG-1 1290 ' 1300 ' FILE SIZE IS SZ PLUS 1310 ' 256 BYTES PER SECTOR 1320 ' IN LAST GRAN PLUS 1330 ' NUM BYTES IN LAST SECT 1340 ' 1350 SZ(DE)=SZ+(SG*256)+BU(DE) 1360 PRINT " ";SZ(DE) 1370 ' 1380 ' SHOW GRANULE MAP 1390 ' 1400 C=0:PRINT " "; 1410 FOR I=0 TO GC-1 1420 PRINT USING"##";GM(I); 1430 C=C+1:IF C=10 THEN PRINT:PRINT " ";:C=0 ELSE PRINT " "; 1440 NEXT:PRINT 1450 ' 1460 ' INCREMENT DIR ENTRY 1470 ' 1480 DE=DE+1 1490 NEXT:NEXT:NEXT 1500 END 1510 ' SUBETHASOFTWARE.COM
Since there is only one big file on this disk, fully filling it, it only has one 68-entry granule chain to print. I modified the code to PRINT#-2 these values to the virtual printer so I could then copy the numbers into the same spreadsheet:
Now it seems clearly obvious that RS-DOS does something different when making a new file, versus what it does when expanding an existing file into a new granule.
I wanted a way to visualize this so, of course, I wrote a program to help me create a full ASCII representation of the granules, then edited the rest by hand.
Interesting! For small files, it alternates tracks starting before Track 17 (FAT/Directory) then after, repeating. For a big file, it starts like that before Track 17, then after and continues to the end of Track 35, then goes before Track 17 and works back to the start of the disk.
The Micro Works Digisector DS-69 / DS-68B digitizers were really cool tech in the 1980s. Looking back, I got to play with video digitizers, the Super Voice speech synthesizer that could “sing”, and even the E.A.R.S. “electronic audio recognition system” for voice commands. All of this on my Radio Shack Color Computer 3 in the late 1980s.
How many decades did it take for this tech to become mainstream in our phones or home assistants? We did it first ;-)
The DS-69 could capture 128×128 or 256×56 photos with 16 grey levels (4-bit greyscale). It also had a mode where it would capture 64 grey scales, though there was no viewer for this and I cannot find any attempts I made to use this mode.
I did, however, find some BASIC which I *think* I wrote that attempted to read a .PIX file and print it out to a printer using different ASCII characters to represent 16 different levels of grey. For example, a space would be bright white at level 0, and a “#” might be the darkest at level 15.
First, GREYTEST.BAS just tried to print blocks using these characters. I was testing.
5 DIM GR(15):FORA=0TO15:READGR(A):NEXT 10 PRINT#-2,"Grey Scale Printer Test:":PRINT#-2 15 FORA=0TO10:FORB=0TO15:PRINT#-2,STRING$(5,GR(B));:NEXT:PRINT#-2:NEXT 99 END 100 REM * Grey Scale Characters (0-15) 105 DATA 32,46,58,45,105,43,61,84,86,37,38,83,65,36,77,20
I asked the Google search engine, and its Gemini A.I. answered:
Dec. ASCII Value Character ----- --------------------------- 32 Space (invisible character) 46 . (period or full stop) 58 : (colon) 45 - (hyphen or minus sign) 105 i (lowercase i) 43 + (plus sign) 61 = (equals sign) 84 T (uppercase T) 86 V (uppercase V) 37 % (percent sign) 38 & (ampersand) 83 S (uppercase S) 65 A (uppercase A) 36 $ (dollar sign) 77 M (uppercase M) 20 NAK (Negative Acknowledge - a non-printable control character)
I must have been manually counting how many “dots” made up the characters and sorting them. I recall starting with the HPRINT font data in ROM (which is what my MiniBanners program used) to count the set dots in each letter, but the printer fonts would be different so I expect this table came from trial and error.
The 20 NAK (non printable) is an odd one, so I wonder if my printer DID print something for that – like a solid block graphic.
Proving memory is not always faulty, I also found TEST.BAS which appeared to open a .PIX file and print it out using this code:
0 POKE150,44:PRINT#-2,CHR$(27)CHR$(33)CHR$(27)CHR$(77)CHR$(27)CHR$(64)CHR$(15) 1 PRINT#-2 5 DIM GR(15):FORA=0TO15:READGR(A):NEXT 10 OPEN"D",#1,"SMILE.PIX",1:FIELD#1,1ASA$ 11 PRINTLOF(1) 15 FORA=1TO64:PRINTA:FORB=0TO127:GET#1,A+B*64:GR=ASC(A$) 20 PRINT#-2,CHR$(GR(GR AND15)); 25 NEXT:PRINT#-2:NEXT:CLOSE 99 END 100 REM * Grey Scale Characters (0-15) 105 DATA 32,46,58,47,62,63,61,84,86,37,38,90,65,69,77,35
I see line 10 opens the file with DIRECT mode with a field size of 1 assigned to string variable A$. This means doing a GET #1,X (where X is a byte offset in the file) would get that byte into A$ so I could get the ASCii value of it (0-15) and use that to know which character to print.
I have no idea if this worked… So let’s give it a try.
I see the program print “8192”, which is the Length Of File. A 128×128 image of bytes would be 16384 in size, so I am guessing each byte has two pixels in it, each 4-bits.
I see I am ANDing off the upper bits in line 20. It looks like I am throwing away every other pixel since no attempt I made to read those other 4-bits. This is likely because this was printing on an 80 column printer, which would not print 128 characters on a line. Instead, 64 would fit.
And, wow! It actually works! I had to reduce the font size down for it to display in the WordPress blog, but here is the output. Step back from the monitor if you can’t see it.
Since this is a symmetrical pattern, if we can figure out how to draw one quadrant, we can draw the others.
The pattern is 19 characters wide, which contains a center column of asterisks, and a left and right column that are spaces except for the center row of asterisks.
“As if they had planned it,” this means the pattern in each quadrants is 8 characters, matching the number of bits in a byte.
I typed it up to figure out what the bit pattern would be. (Actually, I typed up a bit of it, then pasted that into Copilot and had it tell me the bit pattern.)
That’s a mess, but in the left the “.” would represent the blank space down the left side up to the row of 19 asterisks. After that is the 8-bit pattern with “-” representing a space in the pattern (0 bit) and the “*” representing the asterisk (1 bit).
This let me quickly cobble together a proof-of-concept:
1 READ V 2 A$=STRING$(19,32):MID$(A$,10,1)="*" 3 FOR B=0 TO 7 4 IF V AND 2^B THEN MID$(A$,9-B,1)="*":MID$(A$,B+11,1)="*" 5 NEXT 6 PRINT A$:A$(L)=A$ 7 L=L+1:IF L<8 THEN 1 8 PRINT STRING$(18,42) 9 FOR B=7 TO 0 STEP -1:PRINT A$(B):NEXT 10 DATA 2,81,48,114,9,4,162,81
Line 10 are the 8 rows of byte data for a quadrant of the snowflake.
Line 1 reads the first value from the DATA statement.
Line 2 builds a string of 19 spaces, then sets the character at position 10 (in the center) to an asterisk. Every row has this character set.
Line 3 begins a loop representing each bit in the byte (0-7).
Line 4 checks the read DATA value and ANDs it with the bit value (2 to the power of the the FOR/NEXT loop value). If it is set, the appropriate position in the left side of the string is set to an asterisk, and then the same is done for the right side. To mirror, the left side is center-minus-bit, and the right side is center-plus-bit.
Line 5 is the NEXT to continue doing the rest of the bits.
Line 6 prints the completed string, then stores that string in an A$() array. L has not been used yet so it starts at 0.
Line 7 increments L, and as long as it is still ess than 8 (0-7 for the first eight lines of the pattern) it goes back to line 1 to continue with the next DATA statement.
Line 8 once 8 lines have been done, the center row of 19 asterisks is printed.
Line 9 is a loop to print out the A$() lines we saved, backwards. As they were built in line 6, they went from 0 to 7. Now we print them backwards 7 to 0.
…and there we have a simple way to make this pattern, slowly:
Logiker 2025 pattern on a CoCo.
On a CoCo 3, adding a WIDTH 40 or WIDTH 80 before it would show the full pattern:
Logiker 2025 pattern on a CoCo 3.
My example program can be made much smaller by packing lines together and removing unnecessary spaces. One minor optimization I already did was doing the bits from 0 to 7 which removed the need to use “STEP -1” if counting backwards. Beyond that, this is the raw proof-of-concept idea of using bytes.
Other options folks have used in past challenges included rune-length type encoding (DATA showing how many spaces, then how many asterisks, to make the pattern) so that probably is worth investigating to see if it helps here.
Then, of course, someone will probably figure out a math pattern to make this snowflake.
A correction, and discovering the order RS-DOS writes things…
A correction from part 2… This example program had “BIN” and “ASC” mixed up. 0 should represent BINary files, and 255 for ASCii files. I fixed it in line 920. (I will try to edit/fix the original post when I get a moment.)
10 ' FILEINFO.BAS 20 ' 30 ' 0.0 2023-01-25 ALLENH 40 ' 0.1 2023-01-26 ADD DR 50 ' 0.2 2023-01-27 MORE COMMENTS 55 ' 0.3 2025-11-18 BIN/ASC FIX 60 ' 70 ' E$(0-1) - SECTOR HALVES 80 ' FT$ - FILE TYPE STRINGS 90 ' 100 CLEAR 1500:DIM E$(1),FT$(3) 110 FT$(0)="BPRG":FT$(1)="BDAT":FT$(2)="M/L ":FT$(3)="TEXT " 120 ' 130 ' DIR HOLDS UP TO 72 ENTRIES 140 ' 150 ' NM$ - NAME 160 ' EX$ - EXTENSION 170 ' FT - FILE TYPE (0-3) 180 ' AF - ASCII FLAG (0/255) 190 ' FG - FIRST GRANULE # 200 ' BU - BYTES USED IN LAST SECTOR 210 ' SZ - FILE SIZE 220 ' 230 DIM NM$(71),EX$(71),FT(71),AF(71),FG(71),BU(71),SZ(71) 240 ' 250 INPUT "DRIVE";DR 260 ' 270 ' FILE ALLOCATION TABLE 280 ' 68 GRANULE ENTRIES 290 ' 300 DIM FA(67) 310 DSKI$ DR,17,2,G$,Z$:Z$="" 320 FOR G=0 TO 67 330 FA(G)=ASC(MID$(G$,G+1,1)) 340 NEXT 350 ' 360 ' READ DIRECTORY 370 ' 380 DE=0 390 FOR S=3 TO 11 400 DSKI$ DR,17,S,E$(0),E$(1) 410 ' 420 ' PART OF SECTOR 430 ' 440 FOR P=0 TO 1 450 ' 460 ' ENTRY WITHIN SECTOR PART 470 ' 480 FOR E=0 TO 3 490 ' 500 ' DIR ENTRY IS 32 BYTES 510 ' 520 E$=MID$(E$(P),E*32+1,32) 530 ' 540 ' NAME IS FIRST 8 BYTES 550 ' 560 NM$(DE)=LEFT$(E$,8) 570 ' 580 ' EXTENSION IS BYTES 9-11 590 ' 600 EX$(DE)=MID$(E$,9,3) 610 ' 620 ' FILE TYPE IS BYTE 12 630 ' 640 FT(DE)=ASC(MID$(E$,12,1)) 650 ' 660 ' ASCII FLAG IS BYTE 13 670 ' 680 AF(DE)=ASC(MID$(E$,13,1)) 690 ' 700 ' FIRST GRANUAL IS BYTE 14 710 ' 720 FG(DE)=ASC(MID$(E$,14,1)) 730 ' 740 ' BYTES USED IN LAST SECTOR 750 ' ARE IN BYTES 15-16 760 ' 770 BU(DE)=ASC(MID$(E$,15,1))*256+ASC(MID$(E$,16,1)) 780 ' 790 ' IF FIRST BYTE IS 255, END 800 ' OF USED DIR ENTRIES 810 ' 820 IF LEFT$(NM$(DE),1)=CHR$(255) THEN 1390 830 ' 840 ' IF FIRST BYTE IS 0, FILE 850 ' WAS DELETED 860 ' 870 IF LEFT$(NM$(DE),1)=CHR$(0) THEN 1370 880 ' 890 ' SHOW DIRECTORY ENTRY 900 ' 910 PRINT NM$(DE);TAB(9);EX$(DE);" ";FT$(FT(DE));" "; 920 IF AF(DE)=0 THEN PRINT"BIN"; ELSE PRINT "ASC"; 930 ' 940 ' CALCULATE FILE SIZE 950 ' SZ - TEMP SIZE 960 ' GN - TEMP GRANULE NUM 970 ' SG - SECTORS IN LAST GRAN 980 ' 990 SZ=0:GN=FG(DE):SG=0 1000 ' 1010 ' GET GRANULE VALUE 1020 ' GV - GRAN VALUE 1030 ' 1040 GV=FA(GN) 1050 ' 1060 ' IF TOP TWO BITS SET (C0 1070 ' OR GREATER), IT IS THE 1080 ' LAST GRANULE OF THE FILE 1090 ' SG - SECTORS IN GRANULE 1100 ' 1110 IF GV>=&HC0 THEN SG=(GV AND &H1F):GOTO 1280 1120 ' 1130 ' ELSE, MORE GRANS 1140 ' ADD GRANULE SIZE 1150 ' 1160 SZ=SZ+2304 1170 ' 1180 ' MOVE ON TO NEXT GRANULE 1190 ' 1200 GN=GV 1210 GOTO 1040 1220 ' 1230 ' DONE WITH GRANS 1240 ' CALCULATE SIZE 1250 ' 1260 ' FOR EMPTY FILES 1270 ' 1280 IF SG>0 THEN SG=SG-1 1290 ' 1300 ' FILE SIZE IS SZ PLUS 1310 ' 256 BYTES PER SECTOR 1320 ' IN LAST GRAN PLUS 1330 ' NUM BYTES IN LAST SECT 1340 ' 1350 SZ(DE)=SZ+(SG*256)+BU(DE) 1360 PRINT " ";SZ(DE) 1370 DE=DE+1 1380 NEXT:NEXT:NEXT 1390 END 1400 ' SUBETHASOFTWARE.COM
To test this routine, I created a program that let me type a file size (in bytes) and then it would make a .TXT file with that size as the filename (i.e, for 3000 bytes, it makes “3000.TXT”) and then I could run it through this program and see if everything matched.
It opens a file with the size as the filename, then writes out “*” characters to fill the file. This will be painfully slow for large files. If you want to make it much faster, share your work in a comment.
10 ' MAKEFILE.BAS 20 ' 30 ' 0.0 2025-11-18 ALLENH 40 ' 50 INPUT "FILE SIZE";SZ 60 F$=MID$(STR$(SZ),2)+".TXT" 70 OPEN "O",#1,F$ 80 FOR A=1 TO SZ:PRINT #1,"*";:NEXT 90 CLOSE #1 100 DIR 110 GOTO 50 120 ' SUBETHASOFTWARE.COM
I was able to use this program in the Xroar emulator to create files of known sizes so I could verify the FILEINFO.BAS program was doing the proper thing.
It seems to be, so let’s move on…
A funny thing happened on the way to the disk…
I have been digging in to disk formats (OS-9 and RS-DOS) lately, and learning more things I wish I knew “back in the day.” For instance, I was curious how RS-DOS allocates granules (see part 1) when adding files to the disk. I wrote a test program that would write out 2304-byte blocks of data (the size of a granule) full of the number of the block. i.e., for the first write, I’d write 2304 0’s, then 2304 1’s and so on. My simple program looks like this:
10 'GRANULES.BAS 20 OPEN "O",#1,"GRANULES.TXT" 30 FOR G=0 TO 67 40 PRINT G; 50 T$=STRING$(128,G) 60 FOR T=1 TO 18 65 PRINT "."; 70 PRINT #1,T$; 80 NEXT 90 PRINT 100 NEXT 110 CLOSE #1
I ran this on a freshly formatted disk and let it fill the whole thing up. The very last write errors with a ?DF ERROR (disk full) so it never makes it to the close. I guess you can’t write that last byte without an error?
Now I should be able to look a the bytes on the disk and see where the 0’s went, the 15’s went, and so on, and see the order RS-DOS allocated those granules.
I made a simple test program for this:
0 'GRANDUMP.BAS 10 CLEAR 512 20 FOR G=0 TO 67 30 T=INT((G)/2):IF T>16 THEN T=T+1 40 IF INT(G/2)*2=G THEN S1=10:S2=18 ELSE S1=1:S2=9 50 'PRINT "GRANULE";G;TAB(13);"T";T;TAB(20);"S";S1;"-";S2 54 DSKI$0,T,S1,A$,B$ 55 PRINT "GRANULE";G;ASC(A$) 60 NEXT G
Ignore the commented out stuff. Initially I was just getting it to convert a granule to Track/Sectors with code to skip Track 17 (FAT/Directory). And, to be honest, I had an AI write this and I just modified it ;-)
I then modified it to PRINT#-2 to the printer, and ran it in Xroar with the printer redirected to a text file. That gave me the following output:
Now I can see the order that RS-DOS allocates data on an empty disk.
The number in the third column represents the value of the bytes written to that 2304 granule. When I see “GRANULE 67” contains “34” as data, I know it was the 35th (numbers 0-34) granule written out.
Granules 0-33 are on tracks 0-16, then track 17 is skipped, then the remaining granules 34-67 are on tracks 18-34.
You can see that RS-DOS initially writes the data close to track 17, reducing the time it takes to seek from the directory to the file data. This makes sense, though as a teen, I guess I had some early signs of O.C.D. because I thought the directory should be at the start of the disk, and not in the middle ;-)
I brought this data into a spreadsheet, then sorted it by the “data” value (column 3). This let me see the order that granules are allocated (written to). I will add some comments:
GRANULE 33 0 <- first went to gran 33 GRANULE 32 1 <- second went to gran 32
And down the rabbit hole I go. Again. I have tasked an A.I. with creating some simple scripts to manipulate RS-DOS disk images (just for fun; the toolshed “decb” command already exists and works great and does more). While I understood the basic structure for an RS-DOS disk, I did not understand “how” RS-DOS actually allocated those granules. Now I have some insight. Perhaps I can make my tools replicate writing in the same way that RS-DOS itself does.
Look for a part 4. I have some more experiments to share.
Step 1: Rename the .PIX file so it has the extension .data. This is needed for GIMP to recognize it as a “raw” data file.
Step 2: Open this image in GIMP by expanding “Select File Type” and choosing Raw image data. That should allow the .data file to show up in the browser to open it.
Step 3: The file will open and you must adjust settings to tell GIMP more about the image. Under Pixel format, select Grayscale 4-bit. For the Width and Height, set them to 256 (if it is a 32K file) or 128 (if it is 8K). Now you should be able to Open the image.
Step 4: With the image open, you will need to Invert it to get the colors correct (Colors -> Invert) and rotate the image clockwise (Image -> Transform -> Rotate 90 clockwise).
Step 5: That should give you a 256×256 or 128×128 16-greyscale image you can now save out in whatever format you wish. GIMP can save based on the extension you give it when exporting. (File -> Export As… then change the extension to .PNG or .GIF or whatever.)
Tada!
Neat.
Or, I had A.I. write this quick conversion script… It can convert one file at a time, or run it in a directory with .PIX files and it will do them all. It currently only supports the 128×128 16-grey and 256×256 16-grey photos. I recall there was a 64-grey mode, so if I find one of those images, I will update the script to do them, too.
#!/usr/bin/env python3
import sys
import glob
from PIL import Image
def convert_pix(pix_file):
with open(pix_file, 'rb') as f:
data = f.read()
if len(data) == 32768:
width, height = 256, 256
elif len(data) == 8192:
width, height = 128, 128
else:
print(f"Invalid file size for {pix_file} (expected 8192 or 32768 bytes)")
return
pixels = []
for byte in data:
pixels.append(byte >> 4)
pixels.append(byte & 0x0F)
# Create image
img = Image.new('P', (width, height))
img.putdata(pixels)
# Rotate right 90 degrees (CW)
img = img.rotate(-90)
# Invert colors
inverted_pixels = [15 - p for p in img.getdata()]
img.putdata(inverted_pixels)
# Set greyscale palette
palette = []
for i in range(16):
v = i * 255 // 15
palette.extend([v, v, v])
img.putpalette(palette)
# Save as PNG
output_file = pix_file.replace('.PIX', '.png').replace('.pix', '.png')
img.save(output_file)
print(f"Converted {pix_file} ({width}x{height}) to {output_file}")
def main():
if len(sys.argv) == 1:
pix_files = glob.glob('*.PIX') + glob.glob('*.pix')
if not pix_files:
print("No .PIX files found in current directory")
sys.exit(1)
else:
pix_files = sys.argv[1:]
for pix_file in pix_files:
convert_pix(pix_file)
if __name__ == "__main__":
main()
You can find it on my GitHub along with documentation on what all it needs to run:
I am writing this so one of the 6809 experts who reads this can chime in and tell me a better way…
Often I post things so they can get in the search engines in case anyone else looks for that topic later. This is one of those.
Using DEF USR is a great way to put up to ten “easy to execute” routines in an assembly language program. Each of those routines can also do different things based on the numeric (or string) parameter passed in to the USR() call.
If you aren’t trying to be that fancy, but do want multiple functions for whatever reason, what methods are there? Please leave a comment with the best ways to call multiple functions using EXEC from Color BASIC.
Dispatch table
One method that comes to mind is using a dispatch table at the start of the machine language program. If the code is built to compile at &H3F00, then doing an EXEC &H3F00 will run that program. If there are more functions, you have to figure out where they are located and provide those address to the user. This is fine, until you make a change to the code and then those locations shift.
Instead, the start of the program could begin with a series of “branch always” instructions. For example:
org $7f00
start1 bra install start2 bra uninstall
The branch always instruction is one byte, and it is followed by a second byte which is how many bytes away the function is. This makes each entry take two bytes. Thus, install is at &H7F00 and uninstall is at &H7F02. A whole series of functions could be done this way, and the user just has to remember which is which — &H7F00, &H7F02, &H7F04, etc. Having every two bytes be an entry makes it easy to remember.
;------------------------------------------------------------------------------ ; Absolute addresses of ROM calls ;------------------------------------------------------------------------------ CHROUT equ $A002
;------------------------------------------------------------------------------ ; This code can be called by EXEC/EXEC xxxx. ;------------------------------------------------------------------------------ ; Dispatch table at the start of the program. start1 bra install start2 bra uninstall
install leax <msginst,pcr ; X points to message bra print ; print will do the RTS ;rts
uninstall leax <msguninst,pcr ; X points to message ;bra print ; print will do the RTS ;rts
;------------------------------------------------------------------------------ ; PRINT subroutine. Prints the 0-terminated string pointed to by X plus CR ;------------------------------------------------------------------------------ print lda ,x+ beq printdone jsr [CHROUT] bra print printdone lda #13 jmp [CHROUT] ; JMP CHROUT will do an rts. ;rts
;------------------------------------------------------------------------------ ; Data storage for the string messages ;------------------------------------------------------------------------------ msginst fcc "INSTALLED" fcb 0
msguninst fcc "UNINSTALLED" fcb 0
end
One potential issue is that branch can only jump so far. If large functions are being called, you might find they cannot be reached from this dispatch table. One option would be to switch to “long branch”, but then you add more bytes and your dispatch table might be every three bytes – &H7F00, &H7F03, &H7F06, &H7F09, &H7F0C, etc.
That is a fine solution though every 2 may “look” nicer than every 3.
As a workaround, the dispatch table could remain short branches, but they go to a longer one just below it:
org $7f00
start1 bra install start2 bra uninstall
; If a short branch cannot reach, it can call a second long branch: uninstall lbra realuninstall
Above, perhaps “install” is within reach of the “bra”, but “uninstall” is too far away. Simply make the “bra uninstall” branch to a spot with a long branch. A few more bytes, a few more clock cycles, but now the dispatch table can remain “every 2 bytes”.
But there has to be a better way…
Leave your suggestions in the comments.
Until next time…
Bonus
Here is a BASIC loader for that example. RUN it, then EXEC &H7F00 or &H7F02 and be amazed. (Loader generated using Sean Conner’s a09 assembler.)
Hat tip to Erico Monteiro for sending me down another quick benchmarking rabbit hole…
NOTE: This technique will work poorly for ASCII TEXT characters, since the PEEK value is not the same as the PRINT CHR$ value for some characters. It works fine with the graphics blocks (128-255). See the example at the end.
In general, I expect PEEK to be faster than looking up a variable. PEEK only has to process whatever is in the parentheses:
V=PEEK(1024)
Parsing the decimal 1024 can be slow. Using hex is faster (&H400). Using a variable can be even faster (unless there are a ton of variables BASIC has to scan to before finding the target one):
V=PEEK(L)
Erico just showed me technique using an array to store all the characters on the CoCo’s 32 column screen. PRINT@ can be used to put characters on the screen quickly, and when you want to PRINT@ the character somewhere else, you can PRINT@ whatever character used to be there by taking it from the array.
I expected PEEK would be faster than accessing elements of an array so I did a test where I looped through 512 characters using PEEK versus an array:
0' peek-vs-array.bas
10 TIMER=0:FORA=1024 TO 1536 20 Z=PEEK(A) 30 NEXT:PRINT TIMER
40 DIMB(511):TIMER=0:FOR A=0 TO 511 50 Z=B(A) 60 NEXT:PRINT TIMER
At line 10, I loop through all the locations of the 32×16 screen. One by one, Z is set to the value of that location. The value of the loop (1024-1536) matches the POKE/PEEK memory location of the screen.
At line 40, I have an array B() that would be loaded with all the bytes in the screen. The elements of the array (0-511) match the PRINT@ location of the screen.
My results:
123 127
Very close, though the array access is slightly slower. I confirmed PEEK is indeed faster … in this example.
Let’s pretend the loop is a “background” screen and we would PEEK and POKE to restore it versus PRINT@ from the array. (In this example, I am just getting what is there and printing that same thing there again, just for timing.)
0' peek-vs-array2.bas
10 TIMER=0:FOR A=1024 TO 1536 20 Z=PEEK(A):POKEA,Z 30 NEXT:PRINT TIMER
40 DIMB(511):TIMER=0:FOR A=0 TO 511 50 Z=B(A):PRINT@A,CHR$(Z); 60 NEXT:PRINT TIMER
And my results:
210 258
PEEK is faster here, too.
But I have now seen “real code” using this to put a CHR$() player graphic on the screen, and erase it as it moved across the screen (restoring the background as it goes) and the array was faster.
This is another example of why benchmarking a specific item is not always useful. For example, if using PRINT to put things on the screen, you are using the 0-511 location which matches the 0-511 array. If using PEEK, you have one location that is the display screen and another that would be the “saved” background screen. Each time you want to update something, you have to take the location (offset) and add it to the background (to get that one) and the foreground (to get that one). That doubling of math could make it slower versus PRINT@ using 0-511 and CHR$(B(x)) using the same 0-511.
So while PEEK is faster by itself, if you do that and need more math to use it, ARRAYs could win.
50 DIM B(511):TIMER=0:FOR A=0 TO 511 60 Z=B(A):PRINT@A,CHR$(Z); 70 NEXT:PRINT TIMER
The first test loops 0-511 then uses “math” to calculate the background memory location, and more “math” to calculate the foreground memory location. Twice the math, twice the slowness.
The second does not match because the array and PRINT@ location.
333 259
Array is faster than two maths.
But, we can cut that math in half but have the FOR loop go through screen memory, then only add to that to get the background. &H3E00 (15872) background minus &H400 (1024) foreground is &H3A00 (14848). I am using hex because it is quicker for BASIC to parse an &H value than a decimal value.
