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2liners/the art of 2-liners/SCRN_PLOT_your_sound_routine.md
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2liners/the art of 2-liners/SCRN_PLOT_your_sound_routine.md
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# Introduction
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This aricle will explain a new (?) technique to poke subroutines using Applesoft (without using POKEs at ALL :D ) and actually spare several characters if you're into 2-liners.
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## Generating various sounds in 2-liners.
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Using a sound generating routine, we are going to see different techniques to interface assembly routines with Applesoft in the context of 2-liners.
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The routines will be taken of the book "Assembly Lines" by Roger Wagner. The book is available freely as a PDF. It is a goldmine. I'm not sure if this is legal or not but whatever, here's the link to download a copy.
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https://archive.org/details/AssemblyLinesCompleteWagner/mode/2up
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### How it usually works
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We all know that the speaker of the Apple II is rather limited. What's worse is that there's no way in Applesoft to generate other sounds than
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- a beep, using PRINT CHR$(7)
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- a click, by accessing address 49200, for example using a PEEK or a POKE
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The latest technique is called 1-bit sound. It sends a voltage signal to the Apple speaker that will just produce a click because it has been "activated". It is 1-bit because it's either on or off: we're sending voltage or not.
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To generate different tones we need to activate the speaker in two nested loops. The inner loop controls the pitch while the outer loop controls the duration ...
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This is usually done with some 6502 using delays between accesses to memory 49200 ($C030) ...
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One of those routines is provided in Assembly Lines book by Roger Wagner (p. 57).
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The routine is the following:
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```
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0300- A6 07 LDX $07 ; load value in X from byte $07 as duration
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0302- A4 06 LDY $06 ; load value in Y from byte $06 as pitch
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0304- AD 30 C0 LDA $C030 ; activate the "speaker"
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0307- 88 DEY ; decrement the pitch value
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0308- D0 FD BNE $0307 ; until it reaches zero
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030A- CA DEX ; decrement the duration
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030B- D0 F5 BNE $0302 ; until it reaches zero
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030D- 60 RTS ; all done
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```
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Usage from Applesoft is then the following:
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POKE 6, P: POKE 7, D: CALL S
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Where P is the "pitch" and D is the duration ...
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## Integration with Applesoft: the regular way
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But if we want this routine available for Applesoft, we have to either load it from disk (which is not allowed in a 2-liner) or to POKE it into memory before usage.
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Like this:
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10 S=768: FOR L = 0 TO 13 : READ V : POKE S+L ,V : NEXT L: REM 38 + 1 character (":")
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20 DATA 166, 7, 164, 6, 173, 48, 192, 136, 208, 253, 202, 208, 245, 96: REM +53 chars = 92 chars
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As you can see, this takes 92 characters if we were to use it in a 2-liner ...
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And each call to generate a sound would take 21 additional characters assuming we use variables for pitch and duration:
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POKE 6,P : POKE 7,D : CALL S
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## Integration with Applesoft: relocation of routine in page zero
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Can this be reduced ?
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Well, first we could relocate it in page zero ... after all, it's only 14 bytes ... of course this all depends on what you need in page zero.
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For example, bytes $34-$4F are used by Monitor, it is doubtful you have a need for it (but who knows) ... this would result in,
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for example (not all memory location work):
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10 FOR L = 60 TO 73 : READ V : POKE L,V : NEXT L: REM 31+1 chars
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20 DATA 166, 7, 164, 6, 173, 48, 192, 136, 208, 253, 202, 208, 245, 96: REM +53 chars = 85 chars
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Each call to generate a sound would take 22 additional characters (because we didn't store the calling address in S)
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But this is still a lot of bytes just to emit an interesting (?) sound ...
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The main problem is the data we have to poke ... it ranges from 0 to 255 ...
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It means, in basic, values above 99 will take triple the space needed !
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The DATA line, if we omit "DATA" is 49 characters long for only 14 bytes !
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Hexadecimal representation of bytes take only two characters, so it would be only 28 characters in the end. This is the way to explore/experiment.
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There are ways to send monitor commands via Applesoft but even the monitor does not accept less than 3 characters per byte, that is two characters for the byte + one space like "300:16 07 14 06 AD 30 C0 88 D0 FD CA D0 F5 60".
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Such a program would be like this (see http://nparker.llx.com/a2/shlam.html for more info)
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100 A$="300:A6 07 A4 06 AD 30 C0 88 D0 FD CA D0 F5 60 N D823G": REM 58+1 chars
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110 FOR X=1 TO LEN(A$): POKE 511+X,ASC(MID$(A$,X,1))+128: NEXT: REM +52+1 chars = 112 chars
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120 POKE 72,0: CALL -144 : REM + 17 chars = 129 chars
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As you can see, this is worse !
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The simple fact that we need 3 characters to "express" one byte is intolerable ...
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What if we could use hexadecimal (without spaces) right in Applesoft code ?
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Here's a possibility:
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The technique here is a double trick: first it uses the string stored in A$ directly from the Applesoft code (in $800), reading the bytes in A$ as stored in the program in $809 (decimal 2057).
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The second trick is that A$ contains "coded" hexadecimal code. An "A" equals to a "0" and a "P" equals to an "F" (ascii of "A" + 15).
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0->A, 1->B, 2->C, 3->D, 4->E, 5->F, 6->G, 7->H, 8->I, 9->J, A->K, B->L, C->M, D->N, E->O, F->P
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So, A6 07 A4 06 AD 30 C0 88 D0 FD CA D0 F5 60 translates to KG AH KE AG KN DA MA II NA PN MK NA PF GA
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And then we have :
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0 A$="KGAHKEAGKNDAMAIINAPNMKNAPFGA" : REM 33+1 chars
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1 S=768: FOR I = 2057 TO 2084 STEP 2: POKE S+N, (PEEK(I)-65)*16 + PEEK(I+1) - 65: N=N+1: NEXT: REM +74 chars = 108 chars
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That could be further reduced to
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0 A$="KGAHKEAGKNDAMAIINAPNMKNAPFGA" : REM 33+1 chars
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1 S=768: FOR I = 2057 TO 2084 STEP 2: POKE S+N, 16*PEEK(I) + PEEK(I+1) - 1105: N=N+1 : NEXT: REM +71 chars = 105 chars
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Not really helping us !
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So here comes the technique I've developed for this particular case.
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Notice that it can be used for all kinds of subroutines .... just be aware that we're "printing" routines and that the TEXT page lines are not sequential (line 1 is not in $400+40 chars)
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This new (?) technique involves using four very simple instructions: PRINT, SCRN, COLOR and PLOT.
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We will be using the GR/TEXT capabilities of Applesoft to poke a program in TEXT page 1.
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How does it work ?
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First we start from our 14 routine bytes: A6 07 A4 06 AD 30 C0 88 D0 FD CA D0 F5 60
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We leave every number as it is, but we replace all the letters with new letters according to this:
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A becomes J, B becomes K, C->L, D->M, E->N and F becomes O.
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We now have J6 07 J4 06 JM 30 L0 88 M0 OM LJ M0 O5 60
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We will now take advantage of the GR/TEXT screen and the SCRN function.
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We are going to print every low-nibble (4 bits) of each char on line 1 of TEXT (which is line 0 of GR), this means we print "6746M0080MJ050"
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we will print every high-nibble of each char on line 2 of TEXT (which is line 2 of GR), this means we print "J0J0J3L8MOLMO6"
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Then, we will move/copy line 2 of GR, using SCRN to get its "value" (color), to line 1 of GR.
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The result is that in line 0 of GR, we'll have our sound routine.
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Here's the resulting code:
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0 HOME: REM 4 chars (not counted)
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1 ?"6746M0080MJ050": REM 17+1 chars
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2 ?"J0J0J3L8MOLMO6": REM +17+1 chars = 36 chars
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3 FOR I = 0 TO 13 : REM +10+1 chars = 47 chars we're going to SCRN that TEXT line in VTAB 2
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4 COLOR = SCRN(I,2): REM +15+1 chars = 63 chars we have a value 0-15
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5 PLOT I,1: REM +7+1 chars = 71 chars we PLOT it on line 1, actually adding 16*color to the byte in $400+I
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6 NEXT : REM +4 chars = 75 chars
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Even with the "HOME" statement at first (which is needed but might already be included in your 2-liner), we have 75+4+1 chars = 80 chars
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This is still better than the traditional POKE technique ...
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This method can be used to POKE/PLOT longer routines ... just make sure to take into account the fact that one line is 40 chars max, so you
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if you need to handle more bytes, simply add a embracing loop to repeat as needed ... don't forget you can do "NEXT I,J" instead of "NEXT:NEXT" !
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Of course, if you need line 1 of TEXT or line 0 of GR, you'll see the routine ... it's probably better using Hires 2-liners....
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One last thing.
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Roger Wagner's assembly lines contains another routine to handle sound that might be very useful for 2-liners.
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Instead of using
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POKE 6,P: POKE 7,D: CALL 1024
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it's using
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CALL 1024, P, D
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This means saving 12 characters every time you want to emit a sound.
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However, the routine itself (see page 148 of the book) is not 14 bytes but 24 bytes. That's 10 bytes more.
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If you want to output just one "unsual" sound (not CHR$(7) and not PEEK(49200)), use the 14 bytes routine.
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But if you need more tunes, use the 24 bytes routine !
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The 24 bytes routine uses 95 characters by itself ... it's almost as good as the "usual" routine we presented first that had 92 chars but it will take 9 characters less to call it !
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10 HOME : REM 4 (not counted)
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20 ? "0L7660L7676746M0080MJ050" : REM 27+1
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30 ? "24N8024N80J0J0J3L8MOLMO6" : REM +27+1 = 56
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40 FOR I = 0 TO 23 : REM +10+1 chars = 67
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50 COLOR = SCRN(I,2) : REM +15+1 chars = 83
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60 PLOT I,1 : REM +7+1 chars = 91
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70 NEXT: REM +4 chars = 95
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100 REM LET'S HEAR SOMETHING
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120 FOR I = 0 TO 255
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130 CALL 1024 , I, 10
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140 NEXT
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I hope you enjoyed this little tutorial on "how I did it" ! ....
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Can you do better than this ? If so, don't hesitate to post, I'd be happy to see what you've come up with !
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