/
barnstorming.asm
1867 lines (1841 loc) · 54.3 KB
/
barnstorming.asm
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; Annotated disassembly of Barnstorming (NTSC) for Atari 2600
; Assemble with : dasm barnstorming.asm -f3 -obarnstorming.bin
; TIA read registers
CXP0FB = $02
CXPPMM = $07
INPT4 = $0C
; TIA write registers
VSYNC = $00
VBLANK = $01
WSYNC = $02
NUSIZ0 = $04
NUSIZ1 = $05
COLUP0 = $06
COLUP1 = $07
COLUPF = $08
COLUBK = $09
CTRLPF = $0A
REFP0 = $0B
REFP1 = $0C
PF0 = $0D
PF1 = $0E
PF2 = $0F
RESP0 = $10
RESP1 = $11
AUDC0 = $15
GRP0 = $1B
GRP1 = $1C
ENAM0 = $1D
ENAM1 = $1E
HMP0 = $20
HMP1 = $21
HMOVE = $2A
HMCLR = $2B
CXCLR = $2C
; PIA read registers
SWCHA = $0280
SWCHB = $0282
INTIM = $0284
; PIA write registers
TIM64T = $0296
; RAM addresses
GameMode = $80 ; 0-3
GlobalFrameCounter = $81
RNG_82 = $82 ; bit shifting PRNG, only incremented on mode 4 select, used to randomize initial object index for game mode 4
GameModeSwitchCooldown = $83 ; counts down from $1e when holding down select
JoystickInputs = $84 ; 0000rldu, 1 = not pressed, 0 = pressed
ColorsModifier1 = $85 ; used in inactive state to blink screen colors
ColorsModifier2 = $86
Colors = $87 ; $87-$8e, array of length 8
PlayerYPosition = $8f ; $14 (top) - $7d (ground)
PropellerGraphicsCycle = $90 ; 0-2, increases every 4 frames w/o, every 2 frames w/ pressing B
WindmillGraphicsCycle = $91 ; 0-2, increases every 4 frames
BarnsLeftDigitPointers = $92 ; $92-$95, $92 = 10s digit, $94 = 1s digit
GameModeDigitPointer = $96 ; $96-$97, points to graphics of digit displaying the current game mode
PTR_98 = $98 ; $98-$99 used as pointer storage in multiple places
PropellerGraphicsPointer = $9a ; $9a-$9b
BirdGraphicsAnimationPointer = $9c ; $9c-$9d, pointer to current animation frame graphics
; $9e-a1 unused
BarnGraphicsUpperHalf = $a2 ; roof graphics bitfield, 8px chunks, 1=render, usually $ff, used to hide offscreen parts of the barn
BarnGraphicsLowerHalf = $a3 ; wall graphics bitfield, 8px chunks, 1=render, usually $fe, used to hide offscreen parts of the barn, 4px offset to roof
CurrentObjectIndex = $a4 ; index into object data, $00-$3f
NextBirdLaneCycle = $a5 ; values $00-$0f, determines which lane birds will spawn next
WindmillGraphicsPointer = $a6 ; $a6-$a7
InactivityTimer = $a8 ; ticks up every 256 frames, mutes game at $20+, pauses game and flashes colors at $80+
EngineSoundVolume = $a9 ; 0-3, starts at 0, increases after start and never decreases
CollisionDeflectionDirection = $aa ; 0 = up and forward, 1 = down and forward, 2 = up and backward, $ff = no ongoing collision
CollisionCooldownTimerDoubled = $ab ; counts down from $46 upon collision
CollisionCooldownTimer = $ac ; counts down from $23 upon collision
BirdLaneCollisionTimer = $ad ; $ad-af counts down from $30 when colliding with bird on lane
GameWonFlag = $b0 ; $00 when running, $ff when won
ObjectCollisionFlag = $b1 ; bit7 = collided with object
BirdLaneCollisionFlag = $b2 ; $b2-$b4, bit7 = collided with bird lane
InGameTime = $b5 ; $b5-$b8, BCD timer in minutes, seconds, and hundreds, and a binary 1/25600th second counter
InGameTimeDisplayPointers = $b9 ; $b9-$c2
BirdsPassedCounter = $c3 ; $c3-$c5, number of bird formations passed on each lane (%4)
BirdFormation = $c6 ; $b6-$b8, type of bird formation in a lane. 0 = single, 1 = 10 spaced, 2 = 20 spaced, 4 = 40 spaced
AudioControlRegisters = $c9 ; $c9-$ce caches audio control/freq/volume registers, written once per frame
GameStartedFlag = $cf ; started by pressing Button
ActiveBirdLane = $d0 ; bit0-bit2 = top.middle,bottom lane, 1 = birds on lane
PlayerDisabled = $d1 ; game has ended
BarnScoreCooldownTimer = $d2 ; counts down from $50 after scoring a barn to avoid double-scoring
NumberOfBarnsLeft = $d3 ; BCD number
EngineSoundPitch = $d4 ; 0-7, higher = higher pitch
PlayerVerticalSpeed = $d5 ; 0 - $17
PlayerSpeed = $d6
PlayerDisplacement = $d7 ; $d7-$d8, $d7 = vertical, $d8 = horizontal
PlayerDisplacementFractional = $d9 ; $d9-$da, $d9 = vertical, $da = horizontal
TMP_BirdLane_DB = $db
BirdGraphicsAnimationCycle = $dc ; 0-7, increases every 8 frames
FencePostGraphicsPosition = $dd ; horizonal position of fence posts, $9f-$00
Unused_Always0_DE = $de
BarnEndPosition = $df ; descreases from $b7 to $00, by $18 larger than CurrentObjectPosition
; $e0 unused value affected by BirdGraphics_NumberSize loops
BirdGraphics_NumberSize = $e1 ; $e1-$e3; Used in NUSIZ0 register to render birds
; $e4 unused value affected by BirdGraphics_Position loops
BirdGraphics_Position = $e5 ; $e5-$e7
CurrentObjectPosition = $e8 ; descreases from $9f to $00
BirdPosition = $e9 ; $e9-$eb: {bottom, middle, top} lane
BirdGraphics_HMP0 = $ec ; value written to HMP0 register
; $ed unused
BirdGraphicsLaneAnimationLowAddr = $ee ; $ee-$f0: lower byte of current animation frame graphics by lane, uses either $f1 or $f2
BirdGraphicsAnimationLowAddr = $f1 ; lower byte of current animation frame graphics ($ffXX)
BirdGraphicsStartledAnimationLowAddr = $f2 ; lower byte of current animation frame graphics ($ffXX), used if bird were hit
CurrentObjectIsBarnFlag = $f3 ; 1 if current object is barn, 0 if windmill or empty
CurrentObjectRenderFlag = $f4 ; render windmill/weather vane (barn itself is independent from this); affects collisions
TMP_F5 = $f5 ; temporary variable used in multiple places
TMP_F6 = $f6 ; temporary variable used in multiple places
TMP_F7 = $f7 ; temporary variable used in multiple places
TMP_F8 = $f8 ; temporary variable used in multiple places
Unused_F9 = $f9 ; only ever written to, never read
; fa-ff used for stack
processor 6502
ORG $F000
START:
SEI
CLD
LDX #$00
StartupClearMem: LDA #$00
ClearMemoryLoop:
STA $00,X
TXS
INX
BNE ClearMemoryLoop
JSR SetupInitialGameState
LDA RNG_82
BNE MainGameLoop
LDX #$01
STX RNG_82
DEX
JMP ColdBoot
MainGameLoop:
LDX #$07
LF01D: LDA ColorsData,X
EOR ColorsModifier1
AND ColorsModifier2
STA Colors,X
CPX #$01
BCS LF02C
STA COLUBK,X
LF02C: DEX
BPL LF01D
LDA #$21
LDX #$00
JSR LFDBD
LDA #$28
INX
STX CTRLPF
JSR LFDBD
LDA FencePostGraphicsPosition
INX
JSR LFDBD
LDA FencePostGraphicsPosition
CLC
ADC #$40
CMP #$A0
BCC LF04F
SBC #$A0
LF04F: INX
JSR LFD96
STA WSYNC
STA HMCLR
LDX #$03
LF059: LDA BirdPosition-1,X
JSR LFD9E
STA TMP_F5
LDA BirdGraphics_NumberSize-1,X
AND #$0F
ORA TMP_F5
STA BirdGraphics_NumberSize-1,X
STA BirdGraphics_NumberSize-1,X
DEY
DEY
DEY
DEY
STY BirdGraphics_Position-1,X
DEX
BPL LF059
LDA Colors+4
STA COLUBK
LF077: LDY INTIM
BNE LF077
STA WSYNC
STA HMOVE
STY VBLANK
STY NUSIZ0
STY NUSIZ1
LDA #$02
EOR ColorsModifier1
AND ColorsModifier2
STA COLUP0
STA COLUP1
LDX #$01
LF092: STA WSYNC
STA HMOVE
DEX
BPL LF092
LDY #$07
LF09B: STA WSYNC
STA HMOVE
LDA (BarnsLeftDigitPointers+0),Y ; 10s digit
STA GRP0
LDA (BarnsLeftDigitPointers+2),Y ; 1s digit
STA GRP1
DEY
BPL LF09B
JMP LF0F1
ColorsData: .byte $D6,$00,$D0,$1A,$88,$0E,$14,$12
BarnColorsData: .byte $42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42,$42
.byte $42,$42,$42,$42,$42,$42,$42,$42,$D0,$06,$06,$06,$06,$06,$06,$06
.byte $04,$04,$04,$04,$04,$04,$04,$02,$02,$02,$02,$02,$02,$02,$D0,$D6
LF0E5: .byte $FF,$FF,$EE,$88,$00,$00,$00,$00
NumberOfBarnsData: .byte $10,$15,$15,$25
LF0F1: STA WSYNC
STA HMOVE
INY
STY GRP0
STY GRP1
INY
STY NUSIZ1
LDY #$03
STY NUSIZ0
NOP
STA Unused_F9
STA RESP0
STA RESP1
LDX #$01
LF10A: STA WSYNC
STA HMOVE
LDY #$00
STA Unused_F9
DEC TMP_F5
LDA #$07
STA TMP_F5
LDA InGameTimeDisplayPointers+2 ; lower byte of ten seconds digit graphics pointer, used to show/hide decimal points
CMP #$50
DEX
STA HMCLR
BPL LF10A
BCC LF128
STY NUSIZ0
STY NUSIZ1
DEX
LF128: STX TMP_F7
LF12A: LDY TMP_F5
LDA (InGameTimeDisplayPointers),Y
ORA LFDD7,Y
AND TMP_F7
STA GRP0
LDA (InGameTimeDisplayPointers+2),Y
STA GRP1
STA WSYNC
STA HMOVE
LDA (InGameTimeDisplayPointers+8),Y
STA TMP_F6
LDA (InGameTimeDisplayPointers+6),Y
TAX
LDA (InGameTimeDisplayPointers+4),Y
ORA LFDDC,Y
LDY TMP_F6
STA GRP0
STX GRP1
STY GRP0
DEC TMP_F5
BPL LF12A
STA WSYNC
STA HMOVE
LDA #$00
STA GRP0
STA GRP1
JMP LF170
LF162: .byte $14,$14,$0E,$14,$14,$0E,$14,$14,$14,$14,$14,$14,$14,$14
LF170: LDX #$0C
LF172: LDA LFF93,X
EOR ColorsModifier1
AND ColorsModifier2
CPX #$08
BCS LF199
STA WSYNC
STA HMOVE
STA COLUBK
LDA Colors+7
STA COLUPF
LDA LF0E5,X
STA PF0
LDA LFDE4,X
STA PF1
LDA LFDEC,X
STA PF2
JMP LF19F
LF199: STA WSYNC
STA HMOVE
STA COLUBK
LF19F: DEX
BPL LF172
LDX #$00
LDY Colors+0
LDA Colors+3
STA WSYNC
STA HMOVE
STA COLUPF
STY COLUBK
STX PF0
STX PF1
STX PF2
STX NUSIZ1
STX CTRLPF
LDA Colors+2
STA RESP1
STA COLUP1
LDA #$F0
STA HMP1
STA WSYNC
STA HMOVE
JSR LFDBC
JSR LFDBC
STA HMCLR
LDX #$04
STX TMP_BirdLane_DB
LDY PlayerYPosition
LF1D6: STA WSYNC
STA HMOVE
CPY #$15
BCS LF207
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STA PF1
LF1E7: DEX
STX TMP_BirdLane_DB
LDA BirdGraphics_NumberSize-1,X
STA NUSIZ0
STA BirdGraphics_HMP0
LDA #$00
STA PF1
DEY
CPY #$15
BCS LF212
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
LF200: STY TMP_F5
STA PF1
JMP LF21B
LF207: LDA #$00
STA PF1
STA GRP1
STA Unused_F9
JMP LF1E7
LF212: LDA #$00
STA PF1
STA GRP1
JMP LF200
LF21B: STA WSYNC
STA HMOVE
LDA BirdGraphics_Position-1,X
TAX
BMI LF245
CPX #$05
BCS LF271
CPX #$02
BCS LF255
LF22C: DEX
BPL LF22C
NOP
STA RESP0
LF232: JSR LFDBC
LDA #$00
STA PF1
DEY
CPY #$15
BCS LF242
LDA (PropellerGraphicsPointer),Y
STA GRP1
LF242: JMP LF291
LF245: STA Unused_F9
STA Unused_F9
STA Unused_F9
.byte $8D,$10,$00 ; STA $10
LDA #$60
STA HMP0
JMP LF232
LF255: STA Unused_F9
DEX
DEX
STA Unused_F9
LF25B: DEX
BPL LF25B
.byte $8D,$10,$00 ; STA $10
LDA #$00
STA PF1
DEY
CPY #$15
BCS LF26E
LDA (PropellerGraphicsPointer),Y
STA GRP1
LF26E: JMP LF291
LF271: SBC #$05
TAX
DEY
CPY #$15
BCC LF280
STA Unused_F9
DEC TMP_F5
JMP LF285
LF280: LDA (PropellerGraphicsPointer),Y
NOP
STA GRP1
LF285: LDA #$00
STA PF1
STA Unused_F9
LF28B: DEX
BPL LF28B
.byte $8D,$10,$00 ; STA $10
LF291: STA WSYNC
STA HMOVE
CPY #$15
BCC LF29F
NOP
STA Unused_F9
JMP LF2A4
LF29F: LDA LFF45,Y
STA PF1
LF2A4: LDX TMP_BirdLane_DB
BEQ LF308
.byte $AD,$F1,$00 ; LDA BirdGraphicsAnimationLowAddr
STA BirdGraphicsAnimationPointer
LDA BirdGraphics_HMP0
STA HMP0
LDA Colors+5
.byte $8D,$06,$00 ; STA $06
LDX #$0C
LF2B8: LDA Unused_Always0_DE
STA PF1
DEY
CPY #$15
BCS LF2FB
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STA PF1
STY TMP_F5
TXA
TAY
LF2CE: STA HMOVE
LDX TMP_BirdLane_DB
LDA BirdGraphicsLaneAnimationLowAddr-1,X
STA BirdGraphicsAnimationPointer
LDA (BirdGraphicsAnimationPointer),Y
STA GRP0
TYA
TAX
LDY TMP_F5
LDA CXPPMM
STA Unused_F9
STA HMCLR
DEX
BPL LF2B8
LDX #$00
STX BirdGraphics_HMP0
STX PF1
LDX TMP_BirdLane_DB
DEY
ORA CXP0FB
ORA BirdLaneCollisionFlag-1,X
STA BirdLaneCollisionFlag-1,X
STA CXCLR
JMP LF1D6
LF2FB: STA GRP1
STY TMP_F5
TXA
TAY
NOP
NOP
NOP
NOP
JMP LF2CE
LF308: LDA BirdGraphics_HMP0
STA HMP0
STA Unused_F9
STA Unused_F9
LDX #$47
DEY
CPY #$15
BCS LF32A
LDA #$00
STA PF1
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
NOP
NOP
NOP
STA PF1
JMP LF330
LF32A: LDA #$00
STA PF1
STA GRP1
LF330: STA WSYNC
STA HMOVE
JSR LFDBA
JSR LFDBC
STA HMCLR
LDA #$00
STA PF1
INC TMP_F5
DEC TMP_F5
DEY
CPY #$15
BCS LF355
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STA PF1
JMP LF35E
LF355: LDA #$00
STA GRP1
STA PF1
JMP LF35E
LF35E: STA WSYNC
STA HMOVE
LDA CurrentObjectIsBarnFlag
BNE LF3AC
JSR LFDBC
LDA Colors+2
STA COLUP0
NOP
NOP
NOP
NOP
LF371: DEY
LDA #$00
STA PF1
CPY #$15
BCC LF381
STY TMP_F5
TXA
TAY
JMP LF390
LF381: LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STY TMP_F5
STX TMP_F6
LDY TMP_F6
STA PF1
LF390: STA WSYNC
STA HMOVE
CPX #$39
BCS LF39E
LDA LFF5A,Y
JMP LF3A0
LF39E: LDA (WindmillGraphicsPointer),Y
LF3A0: AND CurrentObjectRenderFlag
STA GRP0
LDY TMP_F5
DEX
BPL LF371
JMP LF483
LF3AC: JSR LFDB9
NOP
NOP
STA Unused_F9
LF3B3: DEY
LDA #$00
STA PF1
CPY #$15
BCC LF3C5
STA GRP1
STY TMP_F5
TXA
TAY
JMP LF3D4
LF3C5: LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STY TMP_F5
STX TMP_F6
LDY TMP_F6
STA PF1
LF3D4: STA WSYNC
STA HMOVE
LDA Colors+5
STA COLUP0
LDA BirdGraphicsAnimationFrame0+1,Y
AND CurrentObjectRenderFlag
STA GRP0
LDY TMP_F5
NOP
NOP
NOP
CPX #$30
BEQ LF40A
DEX
BPL LF3B3
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
LF403: STA GRP1
STY TMP_F5
JMP LF420
LF40A: DEX
LF40B: DEY
LDA #$00
STA PF1
CPY #$15
BCS LF403
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STY TMP_F5
NOP
STA PF1
LF420: TXA
TAY
LDA #$07
STA WSYNC
STA HMOVE
STA NUSIZ0
LDA BarnColorsData,Y
EOR ColorsModifier1
AND ColorsModifier2
STA COLUP0
LDA BarnGraphicsUpperHalf
STA GRP0
LDY TMP_F5
DEX
CPX #$18
BCS LF40B
LDA #$E0
STA HMP0
LF442: DEY
LDA #$00
STA PF1
CPY #$15
BCS LF478
LDA (PropellerGraphicsPointer),Y
STA GRP1
LDA LFF45,Y
STY TMP_F5
STA PF1
LF456: TXA
TAY
LDA #$07
NOP
STA HMOVE
STA NUSIZ0
LDA BarnColorsData,Y
EOR ColorsModifier1
AND ColorsModifier2
STA COLUP0
LDA BarnGraphicsLowerHalf
STA GRP0
LDY TMP_F5
STA HMCLR
STA Unused_F9
DEX
BPL LF442
JMP LF483
LF478: STA GRP1
STY TMP_F5
NOP
NOP
NOP
NOP
JMP LF456
LF483: LDA CXPPMM ; collision between P0 (objects) and P1 (propeller)
ORA CXP0FB ; collision between P0 (objects) and PF (body of plane)
ORA ObjectCollisionFlag
STA ObjectCollisionFlag
STA CXCLR
STA WSYNC
STA HMOVE
LDA #$00
STA GRP1
STA GRP0
LDA Colors+2
STA COLUBK
LDA Colors+5
STA COLUP0
STA COLUP1
LDA #$06
STA NUSIZ0
STA NUSIZ1
LDY #$0C
LF4A9: CPY #$07
LDX #$00
BCS LF4B1
LDX #$02
LF4B1: STA WSYNC
STA HMOVE
STX ENAM0
STX ENAM1
LDA LF162,Y
EOR ColorsModifier1
AND ColorsModifier2
STA COLUBK
DEY
BPL LF4A9
LDY #$02
LF4C7: LDA #$00
LDX Colors+6
STA WSYNC
STA HMOVE
STA ENAM0
STA ENAM1
STX COLUBK
DEY
BPL LF4C7
STA WSYNC
STA HMOVE
LDA Colors+1
STA COLUBK
STA WSYNC
STA HMOVE
STA Unused_F9
LDX #$00
STX HMCLR
STX REFP0
STX REFP1
INX
STX NUSIZ0
STA Unused_F9
STA RESP0
STA RESP1
INX
INX
STX NUSIZ1
LDA #$10
STA HMP1
LDY #$07
LF501: LDA (GameModeDigitPointer),Y
STA TMP_F5
STA WSYNC
STA HMOVE
LDA ActivisionLogo0,Y
STA GRP0
LDA ActivisionLogo1,Y
STA GRP1
NOP
LDA ActivisionLogo3,Y
TAX
LDA ActivisionLogo2,Y
STA GRP0
STX GRP1
LDA TMP_F5
STA GRP1
STA HMCLR
DEY
BPL LF501
INY
STY GRP0
STY GRP1
LDA #$21
LDX #$82
STA WSYNC
STA TIM64T
STX VBLANK
LDA #>DigitData0
STA BarnsLeftDigitPointers+1
STA BarnsLeftDigitPointers+3
STA GameModeDigitPointer+1
LDA NumberOfBarnsLeft
AND #$F0
LSR
BNE LF549
LDA #<DigitDataA
LF549: STA BarnsLeftDigitPointers+0
LDX GameMode
INX
TXA
ASL
ASL
ASL
STA GameModeDigitPointer
LDA NumberOfBarnsLeft
AND #$0F
ASL
ASL
ASL
STA BarnsLeftDigitPointers+2
LDY #$08
LDX #$02
LF561: LDA InGameTime,X
AND #$0F
ASL
ASL
ASL
STA InGameTimeDisplayPointers,Y
DEX
BMI LF57C
DEY
DEY
LDA InGameTime+1,X ; skip minutes
AND #$F0
LSR
STA InGameTimeDisplayPointers,Y
DEY
DEY
BPL LF561
LF57C: CLD
LDA PlayerDisabled
BNE LF585 ; does nothing
LDA InactivityTimer
BMI LF585 ; does nothing
LF585: LDA GlobalFrameCounter
AND #$07
BNE LF599
LDX BirdGraphicsAnimationCycle
INX
TXA
AND #$07
STA BirdGraphicsAnimationCycle
TAY
LDA BirdGraphicsAnimationPointerData,Y
STA BirdGraphicsAnimationLowAddr
LF599: LDY #<BirdGraphicsAnimationFrame0
LDA GlobalFrameCounter
AND #$01
BNE LF5A3
LDY #<BirdGraphicsAnimationFrame2
LF5A3: STY BirdGraphicsStartledAnimationLowAddr
LDX #$05
LF5A7: LDY #$00
LDA InactivityTimer
CMP #$20
BCS LF5B5
LDA PlayerDisabled
BNE LF5B5
LDY AudioControlRegisters,X
LF5B5: STY AUDC0,X
DEX
BPL LF5A7
LDA CollisionCooldownTimerDoubled
BNE LF5CC
LDA PlayerSpeed
CMP #$0A
BCS LF5CC
LDA PlayerYPosition
CMP #$7D
BCS LF5CC
INC PlayerYPosition
LF5CC: LDA INTIM
BNE LF5CC
LDY #$82
STY WSYNC
STY VSYNC
STY WSYNC
STY WSYNC
STY WSYNC
STA VSYNC
INC GlobalFrameCounter ;; start of frame
BNE LF5EA
INC InactivityTimer
BNE LF5EA
SEC
ROR InactivityTimer
LF5EA: LDY #$FF
LDA SWCHB
AND #$08
BNE ColorSwitchSetToColor
LDY #$0F
ColorSwitchSetToColor:
TYA
LDY #$00
BIT InactivityTimer
BPL LF600
AND #$F7
LDY InactivityTimer
LF600: STY ColorsModifier1
ASL ColorsModifier1
STA ColorsModifier2
LDA #$30
STA WSYNC
STA TIM64T
LDA SWCHA ; joystick inputs
TAY
LDX CollisionCooldownTimer
BEQ LF617
LDY #$0F ; likely oversight, enables all joystick directions instead of none, meant to be $ff
LF617: TYA
LSR
LSR
LSR
LSR
STA JoystickInputs
INY
BEQ NoJoystickInputs
ButtonActivityDetected:
LDA #$00
STA InactivityTimer
JMP CheckForReset
NoJoystickInputs:
BIT INPT4
BPL ButtonActivityDetected
CheckForReset:
LDA SWCHB
LSR
BCS ResetButtonNotPressed
LDX #$A8
JMP StartupClearMem ; only clear RAM from $a8 onwards with this reset
ResetButtonNotPressed:
LDY #$00
LSR
BCS SelectButtonNotPressed
LDA GameModeSwitchCooldown
BEQ SwitchGameMode
DEC GameModeSwitchCooldown
BPL GameModeSwitchCooldownNotExpired
SwitchGameMode:
INC GameMode
LDA GameMode
CMP #$03
BNE ColdBoot
JSR CycleRNG82
ColdBoot:
LDA GameMode
AND #$03
STA GameMode
STA InactivityTimer
LDA #$AA
STA NumberOfBarnsLeft
STA InGameTime+0
STA InGameTime+1
STA InGameTime+2
STA InGameTime+3
LDA #<DigitDataA
STA InGameTimeDisplayPointers+2 ; lower byte of ten seconds digit graphics pointer, used to show/hide decimal points
LDY #$1E
STY PlayerDisabled
SelectButtonNotPressed:
STY GameModeSwitchCooldown
GameModeSwitchCooldownNotExpired:
LDA InactivityTimer
BMI MainGameLoop_
LDA PlayerDisabled
BEQ ProcessActivePlayer
MainGameLoop_:
JMP MainGameLoop
ProcessActivePlayer:
LDA GameStartedFlag
BNE GameIsAlreadyRunning
BIT INPT4
BPL StartGame
JMP MainGameLoop
StartGame:
LDA #$01
STA GameStartedFlag
STA GlobalFrameCounter
GameIsAlreadyRunning:
BIT GameWonFlag
BPL GameStillOngoing
LDA BirdPosition+2
ORA BirdPosition+0
ORA BirdPosition+1
BNE LF6A1
LDA PlayerYPosition
CMP #$7D
BNE LF6A1
LDA #<PropellerGraphicsDataStanding
STA PropellerGraphicsPointer
INC PlayerDisabled
LF6A1: LDA GlobalFrameCounter
LDX PlayerSpeed
BEQ LF6BA
CPX #$1A
BCS LF6B4
AND #$03
BNE LF6BA
DEC PlayerSpeed
JMP LF6BA
LF6B4: AND #$01
BNE LF6BA
DEC PlayerSpeed