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  1. On entry, PPUMask is #%00011110, all backgrounds set rendering. And PPUCtrl is 88, NMI enabled and sprites from 0x1000 area.
  2.  
  3.   ;ADDED CODE
  4. TestZapperMode:
  5.   BIT PPUStatus
  6.   LDA #$3F
  7.   STA PPUAddr
  8.   LDA #$00
  9.   STA PPUAddr
  10.   LDA #$0F
  11.   TAX
  12. .LoopClearPalette:
  13.   STA $2007
  14.   DEX
  15.   BPL .LoopClearPalette
  16.   JSR WaitForNMI
  17.   LDX #$00
  18.   LDA #$08
  19.   BIT $4016 ;0=Detected; 1=Not detected.
  20.   BEQ .Check1Failed ;No zapper, high/light detected.
  21.   INX
  22. .Check1Failed:
  23.   BIT $4017 ;0=Detected; 1=Not detected.
  24.   BEQ .SeeIfZappers ;No zapper, high/light detected.
  25.   INX
  26.   INX
  27. .SeeIfZappers:
  28.   TXA
  29.   BEQ NoZapperGame ;No zapper used ATM.
  30.   TAY;Y=Which conrollers to check for white. 0000 0021
  31.   BIT PPUStatus ;Reset latch.
  32.   LDA #$3F
  33.   STA PPUAddr
  34.   LDX #$00
  35.   STX PPUAddr
  36.   LDA #$30
  37.   STA PPUData ;Write 30 to first palette space, making whole screen white.
  38.   STX PPUScroll
  39.   STX PPUScroll
  40.   STY Frame ;Frame=Controllers possibly light guns.
  41.  
  42. .KeepPollingZapper:
  43.   TYA ;Put value of possibly zappers in A. Bits=0000 0021
  44.   LSR A ;See if 1 slot is.
  45.   BCC .CheckPlayer2 ;Nope.
  46.   PHA ;Save other bit for now.
  47.   LDA #$08
  48.   LDX #$00
  49.   BIT $4016 ;Test bit.
  50.   BEQ .JumpZapperGame-1 ;If true, PLA and put the zapper slot to X and jump to the game mode.
  51.   PLA ;Retrieve P2 possibly zapper bit.
  52. .CheckPlayer2
  53.   LSR A ;Test P2 possible bit.
  54.   BCC .CheckLoopAgain ;Nope, see if frame has ended now. If not, loop again and keep checking.
  55.   LDA #$08 ;Test bit.
  56.   LDX #$01 ;Zapper value.
  57.   BIT $4017 ;Test
  58.   BNE .CheckLoopAgain ;Nope, no zapper.
  59.   LDA #$68 ;68 is loaded for a PLA instruction, but LDA doesn't hurt this program if it runs anyway, so that's why it's used to PLA in certain circumstances above.
  60. .JumpZapperGame:
  61.   JMP ZapperGame ;Jump to zapper stuff.
  62.  
  63. .CheckLoopAgain:
  64.   CPY Frame ;See if frame is still equal.
  65.   BEQ .KeepPollingZapper ;Yes, keep on going. If not, continue to main game.
  66.  
  67.  
  68. NoZapperGame:
  69.   ;ADDED CODE
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https://ideone.com/Y4tSt
language:
Assembler 32bit (gcc 8.3)
created:
14 years ago
visibility:
public

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