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  "PageContent": "<h3>Sub-Etha Software | \"In Support of the CoCo and OS-9 since 1990!\"</h3>See also:part 1, part 2, part 3, part 4, part 5, part 6, part 7 and part 8.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,&amp;H3F00*   DEFUSR0=&amp;H3F00*   A$=\"Print this in uppercase.\"*   PRINT A$*   A=USR0(VARPTR(A$))*ORGADDR     EQU     $3f00GIVABF      EQU     $B4F4   * 46324INTCNV      EQU     $B3ED   * 46061CHROUT      EQU     $A002opt\t    6809    * 6809 instructions onlyopt\t    cd      * cycle countingorg     ORGADDRstart       jsr     INTCNV  * get passed in value in Dtfr     d,x     * move value (varptr) to Xldy     2,x     * load string addr to Ybeq     null    * exit if strlen is 0ldb     ,x      * load string len to Bldx     #0      * clear X (count of chars conv)loop        lda     ,y+\t    * get next char, inc Y;\t        lda     ,y      * load char in Acmpa    #'a     * compare to lowercase Ablt     nextch  * if less, no conv neededcmpa    #'z     * compare to lowercase Zbgt     nextch  * if greater, no conv neededlcase       suba    #32     * subtract 32 to make uppercaseleax    1,x     * inc count of chars convertednextch      jsr     [CHROUT] * call ROM output character routine;           leay    1,y     * increment Y pointercont        decb            * decrement counterbne\t    loop    * not done yet;           beq     exit    * if 0, go to exit;           bra     loop    * go to loopexit        tfr     x,d     * move chars conv count to Djmp     GIVABF  * return to callernull        ldd     #-1     * load -2 as errorreturn      jmp     GIVABF  * return to caller* lwasm --decb -o ucase2.bin ucase2.asm -l* lwasm --decb -f basic -o ucase2.bas ucase2.asm -l* lwasm --decb -f ihex -o ucase2.hex ucase2.asm -l* decb copy -2 -r ucase2.bin ../Xroar/dsk/DRIVE0.DSK,UCASE2.BINIn 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.See also: Color BASIC and VARPTRNow 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,&amp;H3F00;   DEFUSR0=&amp;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     $3f00CHROUT      EQU     $A002CHKSTR      EQU     $B146       ; Undocumented ROM callINTCNV      EQU     $B3ED       ; 46061GIVABF      EQU     $B4F4       ; 46324org     ORGADDRstart       jsr     CHKSTR      ; ?TM ERROR if not a string.; X will be VARPTR, B will be string lengthtstbbeq     reterror    ; exit if strlen is 0ldy     2,x         ; load string addr to Yldx     #0          ; clear X (count of chars conv)loop        lda     ,y+\t        ; get next char, inc Ycmpa    #'a         ; compare to lowercase Ablo     nextch      ; if less, no conv neededcmpa    #'z         ; compare to lowercase Zbhi     nextch      ; if greater, no conv neededsuba    #32         ; subtract 32 to make uppercaseleax    1,x         ; inc count of chars convertednextch      jsr     [CHROUT]    ; call ROM output character routinedecb                ; decrement counterbne\t    loop        ; not done yettfr     x,d         ; move chars conv count to Dbra     returnreterror    ldd     #-1         ; load -1 as errorreturn      jmp     GIVABF      ; return to callerend; lwasm --decb -o ucase3.bin ucase3.asm -l -m; lwasm --decb -f basic -o ucase3.bas ucase3.asm -l -m; lwasm --decb -f ihex -o ucase3.hex ucase3.asm -l -m; decb copy -2 -r ucase3.bin ../Xroar/dsk/DRIVE0.DSK,UCASE3.BIN; a09 -fbasic -oucase3_a09.bas ucase3.asmHere are the changes… In the original version, I have this:start       jsr     INTCNV  * get passed in value in Dtfr     d,x     * move value (varptr) to Xldy     2,x     * load string addr to Ybeq     null    * exit if strlen is 0ldb     ,x      * load string len to Bldx     #0      * clear X (count of chars conv)That first jsr INTCNV expects a number parameter and, if not a number, it exits with ?TM ERROR. If it gets past that, the number is in the D register and it gets transferred over to X. In this case, the number is the value returned by VARPTR:A=USR0(VARPTR(A$))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 Dtfr     d,x     * move value (varptr) to Xldy     2,x     * load string addr to Yldb     ,x      * load string len to Bbeq     null    * exit if strlen is 0ldx     #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 lengthtstbbeq     reterror    ; exit if strlen is 0ldy     2,x         ; load string addr to Yldx     #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=&amp;H3F00A=USR0(42)?TM ERRORA=USR0(\"This is a test\")THIS IS A TESTAlso, I notice that the value I return can be -1 if you pass in an empty string…A=USR0(\"\")OKPRINT 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.Spot any bugs? Comment, if you will.Until next time…",
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