408 lines
8.8 KiB
Plaintext
408 lines
8.8 KiB
Plaintext
|
|
include "nesdefs.dasm"
|
|
|
|
;;;;; ZERO-PAGE VARIABLES
|
|
|
|
seg.u ZEROPAGE
|
|
org $0
|
|
|
|
Ptr1 .word ; for temporary pointer storage
|
|
|
|
TrackFrac .byte ; fractional position along track
|
|
Speed .byte ; speed of car
|
|
TimeOfDay .word ; 16-bit time of day counter
|
|
; Variables for preprocessing step
|
|
XPos .word ; 16-bit X position
|
|
XVel .word ; 16-bit X velocity
|
|
TPos .word ; 16-bit track position
|
|
TrackLookahead .byte ; current fractional track increment
|
|
; Variables for track generation
|
|
Random .byte ; random counter
|
|
GenTarget .byte ; target of current curve
|
|
GenDelta .byte ; curve increment
|
|
GenCur .byte ; current curve value
|
|
|
|
ZOfs .byte ; counter to draw striped center line
|
|
Weather .byte ; bitmask for weather
|
|
Heading .word ; sky scroll pos.
|
|
|
|
NMITmp .byte
|
|
|
|
NumRoadScanlines = 112
|
|
NumRoadSegments = 56
|
|
; Preprocessing result: X positions for all track segments
|
|
RoadX0 ds NumRoadSegments
|
|
|
|
; Generated track curve data
|
|
TrackLen equ 5
|
|
TrackData ds TrackLen
|
|
|
|
InitialSpeed equ 10 ; starting speed
|
|
|
|
;;;;; OTHER VARIABLES
|
|
|
|
seg.u RAM
|
|
org $300
|
|
|
|
;;;;; NES CARTRIDGE HEADER
|
|
|
|
NES_HEADER 0,2,1,1 ; mapper 0, 2 PRGs, 1 CHR, vert mirror
|
|
|
|
;;;;; START OF CODE
|
|
|
|
Start:
|
|
NES_INIT ; set up stack pointer, turn off PPU
|
|
jsr WaitSync ; wait for VSYNC
|
|
jsr ClearRAM ; clear RAM
|
|
jsr WaitSync ; wait for VSYNC (and PPU warmup)
|
|
|
|
jsr FillVRAM ; set PPU video RAM
|
|
|
|
jsr RoadSetup
|
|
|
|
lda #0
|
|
sta PPU_ADDR
|
|
sta PPU_ADDR ; PPU addr = $0000
|
|
sta PPU_SCROLL
|
|
sta PPU_SCROLL ; scroll = $0000
|
|
lda #MASK_BG|MASK_SPR|MASK_BG_CLIP
|
|
sta PPU_MASK ; enable rendering (first!)
|
|
lda #CTRL_NMI
|
|
sta PPU_CTRL ; enable NMI
|
|
|
|
.endless
|
|
jmp .endless ; endless loop
|
|
|
|
;;;;; ROAD SUBS
|
|
|
|
RoadSetup: subroutine
|
|
lda #1
|
|
sta Random
|
|
lda #InitialSpeed
|
|
sta Speed
|
|
lda #0
|
|
sta TimeOfDay+1
|
|
lda #0
|
|
sta Weather
|
|
rts
|
|
|
|
RoadPreSetup: subroutine
|
|
; Set up some values for road curve computation,
|
|
; since we have some scanline left over.
|
|
lda #0
|
|
sta XVel
|
|
sta XVel+1
|
|
sta XPos
|
|
sta XPos+1
|
|
lda TrackFrac
|
|
sta TPos
|
|
lda #0
|
|
sta TPos+1
|
|
lda #10 ; initial lookahead
|
|
sta TrackLookahead
|
|
rts
|
|
|
|
RoadPostFrame: subroutine
|
|
; Advance position on track
|
|
; TrackFrac += Speed
|
|
lda TrackFrac
|
|
clc
|
|
adc Speed
|
|
sta TrackFrac
|
|
bcc .NoGenTrack ; addition overflowed?
|
|
jsr GenTrack ; yes, generate new track segment
|
|
.NoGenTrack
|
|
; TimeOfDay += 1
|
|
inc TimeOfDay
|
|
bne .NoTODInc
|
|
inc TimeOfDay+1
|
|
lda TimeOfDay+1
|
|
; See if it's nighttime yet, and if the stars come out
|
|
clc
|
|
adc #8
|
|
and #$3f
|
|
cmp #$35
|
|
ror
|
|
sta Weather
|
|
.NoTODInc
|
|
lda Heading
|
|
sec
|
|
sbc XPos+1
|
|
sta Heading
|
|
bit XPos+1
|
|
bmi .NegHeading
|
|
lda Heading+1
|
|
sbc #0
|
|
sta Heading+1
|
|
rts
|
|
.NegHeading
|
|
lda Heading+1
|
|
sbc #$ff
|
|
sta Heading+1
|
|
rts
|
|
|
|
; Compute road curve from bottom of screen to horizon.
|
|
PreprocessCurve subroutine
|
|
ldx #NumRoadSegments-1
|
|
.CurveLoop
|
|
; Modify X position
|
|
; XPos += XVel (16 bit add)
|
|
lda XPos
|
|
clc
|
|
adc XVel
|
|
sta XPos
|
|
lda XPos+1
|
|
adc XVel+1
|
|
sta XPos+1
|
|
sta RoadX0,x ; store in RoadX0 array
|
|
; Modify X velocity (slope)
|
|
; XVel += TrackData[TPos]
|
|
ldy TPos+1
|
|
lda TrackData,y
|
|
clc ; clear carry for ADC
|
|
bmi .CurveLeft ; track slope negative?
|
|
adc XVel
|
|
sta XVel
|
|
lda XVel+1
|
|
adc #0 ; carry +1
|
|
jmp .NoCurveLeft
|
|
.CurveLeft
|
|
adc XVel
|
|
sta XVel
|
|
lda XVel+1
|
|
sbc #0 ; carry -1
|
|
nop ; make the branch timings are the same
|
|
.NoCurveLeft
|
|
sta XVel+1
|
|
; Advance TPos (TrackData index)
|
|
; TPos += TrackLookahead
|
|
lda TPos
|
|
clc
|
|
adc TrackLookahead
|
|
sta TPos
|
|
lda TPos+1
|
|
adc #0
|
|
sta TPos+1
|
|
; Go to next segment
|
|
inc TrackLookahead ; see further along track
|
|
dex
|
|
bpl .CurveLoop
|
|
rts
|
|
|
|
; Generate next track byte
|
|
GenTrack subroutine
|
|
; Shift the existing track data one byte up
|
|
; (a[i] = a[i+1])
|
|
ldx #0
|
|
.ShiftTrackLoop
|
|
lda TrackData+1,x
|
|
sta TrackData,x
|
|
inx
|
|
cpx #TrackLen-1
|
|
bne .ShiftTrackLoop
|
|
; Modify our current track value and
|
|
; see if it intersects the target value
|
|
lda GenCur
|
|
clc
|
|
adc GenDelta
|
|
cmp GenTarget
|
|
beq .ChangeTarget ; target == cur?
|
|
bit GenTarget ; we need the sign flag
|
|
bmi .TargetNeg ; target<0?
|
|
bcs .ChangeTarget ; target>=0 && cur>=target?
|
|
bcc .NoChangeTarget ; branch always taken
|
|
.TargetNeg
|
|
bcs .NoChangeTarget ; target<0 && cur<target?
|
|
; Generate a new target value and increment value,
|
|
; and make sure the increment value is positive if
|
|
; the target is above the current value, and negative
|
|
; otherwise
|
|
.ChangeTarget
|
|
lda Random
|
|
jsr NextRandom ; get a random value
|
|
sta Random
|
|
and #$3f ; range 0..63
|
|
sec
|
|
sbc #$1f ; range -31..32
|
|
sta GenTarget ; -> target
|
|
cmp GenCur
|
|
bmi .TargetBelow ; current > target?
|
|
lda Random
|
|
jsr NextRandom ; get a random value
|
|
sta Random
|
|
and #$f ; mask to 0..15
|
|
jmp .TargetAbove
|
|
.TargetBelow
|
|
lda Random
|
|
jsr NextRandom
|
|
sta Random
|
|
ora #$f0 ; mask to -16..0
|
|
.TargetAbove
|
|
ora #1 ; to avoid 0 values
|
|
sta GenDelta ; -> delta
|
|
lda GenCur
|
|
.NoChangeTarget
|
|
; Store the value in GenCur, and also
|
|
; at the end of the TrackData array
|
|
sta GenCur
|
|
sta TrackData+TrackLen-1
|
|
rts
|
|
|
|
|
|
; fill video RAM
|
|
FillVRAM: subroutine
|
|
PPU_SETADDR $2000
|
|
lda #<RoadTables
|
|
sta Ptr1
|
|
lda #>RoadTables
|
|
sta Ptr1+1
|
|
ldx #8
|
|
ldy #0
|
|
.loop:
|
|
lda (Ptr1),y
|
|
sta PPU_DATA
|
|
iny
|
|
bne .loop
|
|
inc Ptr1+1
|
|
dex
|
|
bne .loop
|
|
rts
|
|
|
|
; set palette colors
|
|
SetPalette: subroutine
|
|
PPU_SETADDR $3f00
|
|
ldx #16
|
|
.loop:
|
|
lda Palette,y
|
|
sta PPU_DATA
|
|
iny
|
|
dex
|
|
bne .loop
|
|
rts
|
|
|
|
; set sprite 0 (A = top scanline)
|
|
SetSprite0: subroutine
|
|
sta $200 ;ypos
|
|
lda #$00 ;code
|
|
sta $201
|
|
lda #$20 ;flags
|
|
sta $202
|
|
lda #$f0 ;xpos
|
|
sta $203
|
|
rts
|
|
|
|
;;;;; COMMON SUBROUTINES
|
|
|
|
include "nesppu.dasm"
|
|
|
|
;;;;; INTERRUPT HANDLERS
|
|
|
|
MAC SLEEP ;usage: SLEEP n (n>1)
|
|
.CYCLES SET {1}
|
|
|
|
IF .CYCLES < 2
|
|
ECHO "MACRO ERROR: 'SLEEP': Duration must be > 1"
|
|
ERR
|
|
ENDIF
|
|
|
|
IF .CYCLES & 1
|
|
bit $00
|
|
.CYCLES SET .CYCLES - 3
|
|
ENDIF
|
|
|
|
REPEAT .CYCLES / 2
|
|
nop
|
|
REPEND
|
|
ENDM
|
|
|
|
;;;
|
|
;;; NMI HANDLER
|
|
;;;
|
|
|
|
NMIHandler: subroutine
|
|
; save registers
|
|
SAVE_REGS
|
|
; cycle palette colors
|
|
lda TPos ; track position
|
|
lsr ; / 2
|
|
and #16 ; now either 0 or 16
|
|
tay ; Y is palette offset
|
|
jsr SetPalette ; call SetPalette
|
|
PPU_SETADDR $2000 ; reset PPU address
|
|
; load sprite zero
|
|
lda #109
|
|
jsr SetSprite0 ; set sprite 0 position
|
|
lda #$02
|
|
sta PPU_OAM_DMA ; send sprites to PPU
|
|
; setup sky scroll
|
|
lda Heading+1 ; heading scroll pos.
|
|
sta PPU_SCROLL ; X scroll
|
|
lda #0
|
|
sta PPU_SCROLL ; Y scroll = 0
|
|
; do road calculations
|
|
jsr RoadPreSetup
|
|
jsr PreprocessCurve
|
|
jsr RoadPostFrame
|
|
; wait for sprite 0
|
|
.wait0 bit PPU_STATUS
|
|
bvs .wait0 ; until bit 6 set
|
|
.wait1 bit PPU_STATUS
|
|
bvc .wait1 ; until bit 6 clear
|
|
; start scanline loop
|
|
ldy #0 ; scanline counter
|
|
lda #3
|
|
sta NMITmp ; count every 3 lines
|
|
.loop
|
|
; take back 1 cycle every 3rd line
|
|
dec NMITmp ; decrement 3-line counter
|
|
beq .resetx ; has it been 3 lines?
|
|
; pad out rest of the scanline
|
|
SLEEP 10
|
|
.skipcyc
|
|
SLEEP 70
|
|
; change scroll register
|
|
tya ; Y -> A
|
|
lsr ; A / 2
|
|
tax ; A -> X
|
|
lda RoadX0,x ; get X offset of scanline
|
|
eor #$80 ; + 128
|
|
sta PPU_SCROLL ; horiz byte
|
|
sta PPU_SCROLL ; vert byte (ignored)
|
|
; next loop iteration
|
|
iny
|
|
cpy #NumRoadScanlines
|
|
bcc .loop ; do next scanline
|
|
; restore registers and return from interrupt
|
|
RESTORE_REGS
|
|
rti
|
|
; this resets the 3-line counter
|
|
; and returns to a different loop entry point
|
|
; since we wasted 8 cycles doing this
|
|
.resetx
|
|
lda #3
|
|
sta NMITmp ; reset 3-line counter
|
|
bne .skipcyc ; go back to loop
|
|
|
|
;;;;; CONSTANT DATA
|
|
|
|
;;{pal:"nes",layout:"nes"};;
|
|
Palette:
|
|
hex 0F3F06300F19063F0F1916063F180801
|
|
hex 0F30163F0F19163F0F1906160F180801
|
|
;;
|
|
RoadTables:
|
|
incbin "road/nametable.dat"
|
|
incbin "road/attribute.dat"
|
|
incbin "road/nametable1.dat"
|
|
incbin "road/attribute1.dat"
|
|
|
|
;;;;; CPU VECTORS
|
|
|
|
NES_VECTORS
|
|
|
|
;;;;; TILE SETS
|
|
|
|
org $10000
|
|
incbin "road/road.chr"
|
|
incbin "road/road.chr"
|