mirror of
https://github.com/RevCurtisP/C02.git
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157 lines
5.1 KiB
Plaintext
157 lines
5.1 KiB
Plaintext
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/* Atari VCS Color Bars Program */
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#pragma origin $F800 //2k Cartridge
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#include <vcshead.h02> //TIA and RIOT Registers
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#include <vcsinit.h02> //Initialize VCS
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zeropage char clrbkg; //Color Background
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zeropage char clrofs; //Color Offset
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zeropage char clrmsk; //Color/B&W Mask
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zeropage char score; //Two Digit BCD Score
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zeropage char timer; //Two Digit BDC Timer
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zeropage char scrone; //Offset into Ones Digit
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zeropage char tmrone;
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zeropage char scrten; //Offset into Tens Digit
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zeropage char tmrten;
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zeropage char scrgfx; //Score Graphics Data
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zeropage char tmrgfx; //Score Timer Graphics
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zeropage char temp; //Scratch Variable
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/* Generate Ones Digit Offset */
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char ofsone() {
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temp = A & $0F;
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temp++;
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A<<; A<<;
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return A + temp;
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}
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/* Generate Tens Digit Offset */
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char ofsten() {
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A = A & $F0;
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A>>; A>>;
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temp = A;
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temp++;
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A>>; A>>;
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return A + temp;
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}
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/* Prepare Score and Timer for Display */
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void prepst() {
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scrone = ofsone(score);
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scrten = ofsten(score);
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tmrone = ofsone(timer);
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tmrten = ofsten(timer);
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}
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/* Display Score and Timer */
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void dispst() {
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X = 5; //5 lines in digit
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}
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ScoreLoop: ; 43 - cycle after bpl ScoreLoop
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ldy DigitTens ; 3 46 - get the tens digit offset for the Score
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lda DigitGfx,y ; 5 51 - use it to load the digit graphics
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and #$F0 ; 2 53 - remove the graphics for the ones digit
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sta ScoreGfx ; 3 56 - and save it
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ldy DigitOnes ; 3 59 - get the ones digit offset for the Score
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lda DigitGfx,y ; 5 64 - use it to load the digit graphics
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and #$0F ; 2 66 - remove the graphics for the tens digit
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ora ScoreGfx ; 3 69 - merge with the tens digit graphics
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sta ScoreGfx ; 3 72 - and save it
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sta WSYNC ; 3 75 - wait for end of scanline
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;---------------------------------------
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sta PF1 ; 3 3 - @66-28, update playfield for Score dislay
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ldy DigitTens+1 ; 3 6 - get the left digit offset for the Timer
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lda DigitGfx,y ; 5 11 - use it to load the digit graphics
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and #$F0 ; 2 13 - remove the graphics for the ones digit
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sta TimerGfx ; 3 16 - and save it
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ldy DigitOnes+1 ; 3 19 - get the ones digit offset for the Timer
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lda DigitGfx,y ; 5 24 - use it to load the digit graphics
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and #$0F ; 2 26 - remove the graphics for the tens digit
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ora TimerGfx ; 3 29 - merge with the tens digit graphics
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sta TimerGfx ; 3 32 - and save it
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jsr Sleep12 ;12 44 - waste some cycles
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sta PF1 ; 3 47 - @39-54, update playfield for Timer display
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ldy ScoreGfx ; 3 50 - preload for next scanline
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sta WSYNC ; 3 53 - wait for end of scanline
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;---------------------------------------
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sty PF1 ; 3 3 - @66-28, update playfield for the Score display
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inc DigitTens ; 5 8 - advance for the next line of graphic data
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inc DigitTens+1 ; 5 13 - advance for the next line of graphic data
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inc DigitOnes ; 5 18 - advance for the next line of graphic data
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inc DigitOnes+1 ; 5 23 - advance for the next line of graphic data
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jsr Sleep12 ;12 35 - waste some cycles
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dex ; 2 37 - decrease the loop counter
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sta PF1 ; 3 40 - @39-54, update playfield for the Timer display
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bne ScoreLoop ; 2 42 - (3 43) if dex != 0 then branch to ScoreLoop
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sta WSYNC ; 3 45 - wait for end of scanline
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;---------------------------------------
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stx PF1 ; 3 3 - x = 0, so this blanks out playfield
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sta WSYNC ; 3 6 - wait for end of scanline
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/* Generate Vertical Sync Signal */
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void vtsync() {
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X=49; //49*64 Cycles (37 Scanlines)
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A=2; //Set Bit 2 (D1)
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WSYNC=A; //Wait for end of Scanline
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VSYNC=A; //Turn On Vertical Sync
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TIM64T=X; //Set Timer
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WSYNC=A; //Wait 2 More Scanlines
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WSYNC=A;
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A=0; //Clear Bit 2 (D1)
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WSYNC=A; //Wait for End of 3rd Scanline
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VSYNC=A; //Turn Off Vertical Sync
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return;
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}
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/* Execute Vertical Blank Code */
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void vtblnk() {
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clrmsk = (SWCHB & 8) ? $FF : $0F;
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if (SWCHB & 64) clrofs--; else clrofs++;
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A=0; //Clear All Bits
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return;
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}
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/* Execute Kernel Code */
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void kernel() {
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do WSYNC=A; while(INTIM);
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VBLANK=0; //Turn Off Vertical Blank
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X=192; //Draw 192 Scanlines
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do {
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clrbkg = X;
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if (!SWCHB & 128) clrbkg<<;
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A = clrbkg + clrofs & clrmsk; //Set Background Color
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WSYNC = A; //Wait for end of Scanline
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COLUBK = A; //Set Background Color
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X--;
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} while (X);
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return;
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}
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/* Execute Overscan Code */
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void ovrscn() {
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WSYNC=A; //Wait for end of Scanline
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A=2; //Set Bit 2 (D1)
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VBLANK=A; //Turn On Vertical Blank
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TIM64T = 32; //Delay 32*64 Cycles (27 Scanlines)
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do {
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WSYNC=A; //Wait for end of Scanline
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} while(INTIM);
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return;
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}
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irqbrk: //Code to Execute when BRK Instruction is Encountered
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main: //Start of Program Code
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vtsync(); //Generate Vertical Sync Signal
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vtblnk(); //Generate Vertical Blank Signal
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kernel(); //Execute Kernal Code
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ovrscn(); //Execute Overscan Code
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goto main;
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#include <vcsfoot.h02> //Finalization Code
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