mirror of https://github.com/RevCurtisP/C02.git
73 lines
1.8 KiB
Plaintext
73 lines
1.8 KiB
Plaintext
/* 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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/* 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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