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132 lines
4.4 KiB
Plaintext
132 lines
4.4 KiB
Plaintext
;k2line.a02 - Two Line Kernal Assembly Language File for C02
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;Requires Constants PLYR0H and PLYR1H,
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;Variables PLYR0D and PLYR1D, and Pointers PLYR0P and PLYR1P
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PLYR0H EQU $D0 ;Player 0 Height
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PLYR1H EQU $D1 ;Player 1 Height
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PLYR0D EQU $D2 ;Player 0 Draw Counter
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PLYR1D EQU $D3 ;Player 1 Draw Pointer
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PLYR0P EQU $D4 ;Player 0 Graphics Pointer
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PLYR1P EQU $D6 ;Player 1 Graphics Pointer
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PLYR0T EQU $D8 ;Player 0 Pointer Offset
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PLYR1T EQU $DA ;Player 1 Pointer Offset
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SCNLNS EQU $DF ;Number of Scanlines
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;setpl0() - Set Player 0 Data
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;Args: A = Player 0 Height
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; Y,X = Pointer to Player 0 Graphics Data
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SETPL0: STA PLYR0H ;Save Player 0 Height
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DEC PLYR0H ;and Decrement
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STX PLYR0P ;Save Player 0 Pointer
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STY PLYR0P+1
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RTS
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;setpl1() - Set Player 1 Data
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;Args: A = Player 1 Height
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; Y,X = Pointer to Player 1 Graphics Data
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SETPL1: STA PLYR1H ;Save Player 1 Height
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DEC PLYR1H ;and Decrement
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STX PLYR1P ;Save Player 1 Pointer
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STY PLYR1P+1
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RTS
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;prppl0() - Prep Player Variables
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;Args: A = Player 0 Y-Position
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PRPPL0: LDX #1 ;Divide Y-Position by 2
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SEC
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SBC #1
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LSR ;and Set Vertical Delay if No Remainder
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STA TEMP0
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BCS PRPPN0
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STX VDELP0
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PRPPN0: LDA SCNLNS ;PLYR0D = SCNLNS + PLYR0H - PLYR0Y
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CLC
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ADC PLYR0H
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SEC
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SBC TEMP0
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STA PLYR0D
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LDA PLYR0P ;PLYR0T = PLYR0P + PLYR0H - PLYR0Y - 1
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CLC
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ADC PLYR0H
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SEC
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SBC TEMP0
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STA PLYR0T
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LDA PLYR0P+1
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SBC #0
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STA PLYR0T+1
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RTS
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;prppl1() - Prep Player 1 Variables
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;Args: A = Player 1 Y Position
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PRPPL1: LDX #1
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CLC ;Increment Y-Position
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ADC #1 ; to compensate for priming of GRP1
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LSR ;Divide by 2
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STA TEMP1 ; and set Vertical Delay if No Remainder
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BCS PRPPN1
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STX VDELP1
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PRPPN1: LDA SCNLNS ;PLYR1D = SCNLNS + PLYR1H - PLYR1Y
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CLC
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ADC #1
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ADC PLYR1H
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SEC
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SBC TEMP1
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STA PLYR1D
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LDA PLYR1P ;PLYR1T = PLYR1P + PLYR1H - PLYR1Y - 1
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CLC
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ADC PLYR1H
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SEC
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SBC TEMP1
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STA PLYR1T
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LDA PLYR1P+1
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SBC #
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STA PLYR1T+1
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RTS
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;prpdsp() - Prep Display
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PRPDSP: LDA #0
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STA WSYNC ;Wait for Horizontal Sync
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STA HMOVE ;Move Objects
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STA VDELP0 ;Clear Player 0 Vertical Delay
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STA VDELP1 ;Clear Player 0 Vertical Delay
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RTS
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;dsplns() - Display Two Line Kernal
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DSPLNS: LDY SCNLNS ; (13) Set Number of Lines to Draw
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LDA PLYR1H ; 2 9 - Get Player 1 Height
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DCP PLYR1D ; 5 14 - Decrement counter and compare with height
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BCS DSPLNP ; 2 16 - (3 18) If not on current scanline
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LDA #0 ; 2 18 - Load Blank Line
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BYTE $2C ; 4 22 - Else (BIT trick)
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DSPLNP: LDA (PLYR1T),Y ; 5 22 - Load Player 0 Graphics Line
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STA GRP1 ; 3 25 - Set Player 0 Graphics Data
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DEY
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DSPLNL: LDA PLYR0H ;2 21 - Height of Player 0 (Zero Based)
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DCP PLYR0D ;5 26 - Decrement counter and compare with height
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BCS DSPLN0 ;2 28 - (3 23) If Player 0 not on Current Scanline
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LDA #0 ;2 30 - Load Blank Line
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BYTE $2C ;4 34 - Else (BIT trick)
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DSPLN0: LDA (PLYR0T),Y ;5 49 - Load Player 0 Graphics Line
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STA WSYNC ;3 52 - End of Line 2
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STA GRP0 ;3 3 - Set Player 0 Graphics Data
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LDX #%11111111 ;2 5 - Load Playfield Pattern
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STX PF0 ;3 8 - and Store
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STX PF1 ;3 11
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STX PF2 ;3 14
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LDA PLYR1H ;2 16 - Get Player 1 Height
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DCP PLYR1D ;5 21 - Decrement counter and compare with height
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BCS DSPLN1 ;2 23 - (3 18) If not on current scanline
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LDA #0 ;2 25 - Load Blank Line
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BYTE $2C ;4 29 - - Else (BIT trick)
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DSPLN1 LDA (PLYR1T),Y ;5 34 - Load Player 1 Graphics Line
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STA WSYNC ;3 37 - End of Line 1
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STA GRP1 ;3 3 - Set Player 0 Graphics Data
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LDX #0 ;2 5 - Load Playfield Pattern
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STX PF0 ;3 8 - and Store
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STX PF1 ;3 11
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STX PF2 ;3 14
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DEY ;2 16 - decrease the 2LK loop counter
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BPL DSPLNL ;2 18 - (3 21) Branch if more lines to draw
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RTS
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