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https://github.com/RevCurtisP/C02.git
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125 lines
4.2 KiB
Plaintext
125 lines
4.2 KiB
Plaintext
;k2line.a02 - Two Line Kernal Assembly Language File for C02
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;Requires ConSTAnts KNLLNS, P0HGHT and P1HGHT
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;Set Kernel Top Line
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;;TODO - Adjust for Extra WSYNC in DSPLNS
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;; Need to Execute a second WSYNC if KNLLNS is Even
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KNLTOP EQU KNLLNS/2-1 ;Kernel Lines / 2 Scanlines - 1 (Zero Based)
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P0DRAW EQU $D0 ;Player 0 Draw Counter
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P1DRAW EQU $D1 ;Player 1 Draw Counter
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P0PTRL EQU $D2 ;Player 0 Graphics Pointer
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P0PTRH EQU $D3
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P1PTRL EQU $D4 ;Player 0 Graphics Pointer
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P1PTRH EQU $D5
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;p0prep() - Prepare Player 0 for Display
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;Args: A - Y-Position
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; X,Y - Address of Graphics Data
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;Uses: KNLLNS, P0HGHT
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;Sets: TEMP0 - Y-Position
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;Affects; A,C,N,Z
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P0PREP: LSR ;Divide by 2 for Two-line Position
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STA TEMP0 ;Save Y Position
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ROL ;Rotate Carry into Bit 1
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EOR #1 ;Reverse It
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STA VDELP0 ;and Store in Vertical Delay Register
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LDA #KNLTOP ;Draw = Top Line + Height - Y Position
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CLC
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ADC #P0HGHT
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SEC
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SBC TEMP0
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STA P0DRAW
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TXA ;Pointer = GfxAddr + Height - 1 - Y Position
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CLC
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ADC #P0HGHT-1
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TAX
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TYA
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ADC #0
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TAY
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TXA
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SEC
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SBC TEMP0
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STA P0PTRL
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TYA
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SBC #0
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STA P0PTRH
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RTS
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;p1prep() - Prepare Player 1 for Display
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;Args: A - Y-Position
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; X,Y - Address of Graphics Data
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;Uses: KNLLNS, P1HGHT
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;Sets: TEMP1 - Y-Position
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;Affects; A,C,N,Z
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P1PREP: CLC ;Add 1 to Y-Position
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ADC #1 ;to Compensate for GRP1 Priming
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LSR ;Divide by 2 for Two-line Position
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STA TEMP1 ;Save Y Position
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ROL ;Rotate Carry into Bit 1
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EOR #1 ;Reverse It
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STA VDELP1 ;and Store in Vertical Delay Register
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LDA #KNLTOP ;Draw = Top Line + Height - Y Position + 1
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CLC
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ADC #P1HGHT+1
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SEC
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SBC TEMP1
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STA P1DRAW
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TXA ;Pointer = GfxAddr + Height - 1 - Y Position
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CLC
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ADC #P1HGHT-1
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TAX
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TYA
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ADC #0
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TAY
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TXA
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SEC
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SBC TEMP1
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STA P1PTRL
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TYA
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SBC #0
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STA P1PTRH
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RTS
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;dsplns() - Kernel Display Routine
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;Args: None
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;Uses: KNLLNS, P0HGHT, P1HGHT, P0PTRL, P1PTRL
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;Affects: A,X,Y,C,N,Z
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DSPLNS: LDY #KNLTOP+1 ; - Number of Kernal Lines (Scanlines / 2)
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LDA #1 ; - Reflect Playfield
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STA CTRLPF ; - Set Playfield Control Register
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LDA #P1HGHT-1 ; - Preset GRP1 if Player 1 on Top Line
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DCP P1DRAW ;
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BCS DSPLN0 ;
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LDA #0 ;
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BYTE $2C ;
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DSPLN0: LDA (P1PTRL),Y ;
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STA GRP1 ; 3 6
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DEY ; 2 8
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AND ($FF),Y ; 5 13 - Waste 5 Cycles to Match Line 2 Loop
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DSPLNL: LDA #P0HGHT-1 ; 2 15 - Player 1 Height minus 1 due to STArting with 0
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DCP P0DRAW ; 5 20 - Decrement P0DRAW and compare with height
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BCS DSPLN1 ; 2 22 - If Player 0 not on Current Scanline
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LDA #0 ; 2 24 - Load 0 (No Graphics)
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BYTE $2C ; 4 28 - Else (BIT trick)
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DSPLN1: LDA (P0PTRL),Y ;(5 28)- Load Player 0 Graphics Line
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STA WSYNC ; 3 31 - STArt Line 2
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STA GRP0 ; 3 3 - Set Player 0 Graphics Data
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LDX #%11111111 ; 2 5 - Set Playfield Pattern for
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STX PF0 ; 3 8 - Vertical Alignment Testing
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LDA #P1HGHT-1 ; 2 10 - Player 1 Height minus 1 due to STArting with 0
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DCP P1DRAW ; 5 15 - Load 0 (No Graphics)
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BCS DPSLN2 ; 2 17 - If Player 1 not on Current Scanline
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LDA #0 ; 2 19 - Load 0 (No Graphics)
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BYTE $2C ; 4 23 - Else (BIT trick)
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DPSLN2: LDA (P1PTRL),Y ;(5 23)- Load Player 1 Graphics Line
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STA WSYNC ; 3 26 - STArt Line 2
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STA GRP1 ; 3 3 - Set Player 1 Graphics Data
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LDX #0 ; 2 5 - Set Playfield Pattern for
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STX PF0 ; 3 8 - Vertical Alignment Testing
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DEY ; 2 10 - Decrement Loop Counter
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BPL DSPLNL ; 2 12 - and Loop if >= 0
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RTS
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