mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-06-13 09:29:35 +00:00
112 lines
2.6 KiB
NASM
112 lines
2.6 KiB
NASM
.arch ../../presets/verilog/femto8 ; FEMTO-8 architecture
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.org 128 ; origin = 128 ($80)
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.len 128 ; length = 128 ($80)
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; define constants
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.define PADDLE_X 0
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.define PADDLE_Y 1
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.define PLAYER_X 2
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.define PLAYER_Y 3
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.define ENEMY_X 4
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.define ENEMY_Y 5
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.define ENEMY_DIR 6
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.define SPEED 7
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.define TRACKPOS_LO 8
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.define TRACKPOS_HI 9
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.define IN_HPOS $40
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.define IN_VPOS $41
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.define IN_FLAGS $42
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.define F_DISPLAY 1
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.define F_HPADDLE 2
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.define F_VPADDLE 4
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.define F_HSYNC 8
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.define F_VSYNC 16
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.define F_COLLIDE 32
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Start:
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lda #128 ; load initial positions
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sta PLAYER_X ; player_x = 128
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sta ENEMY_X ; enemy_x = 128
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sta ENEMY_Y ; enemy_y = 128
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lda #180
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sta PLAYER_Y ; player_y = 180
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zero A
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sta SPEED ; player speed = 0
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inc A
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sta ENEMY_DIR ; enemy dir = 1 (right)
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; read horizontal paddle position
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DisplayLoop:
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; lda #F_HPADDLE ; paddle flag -> A
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; ldb #IN_FLAGS ; addr of IN_FLAGS -> B
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; and none,[B] ; read B, AND with A
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; bz DisplayLoop ; loop until paddle flag set
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ldb #IN_VPOS
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mov A,[B] ; load vertical position -> A
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sta PLAYER_X ; store player x position
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; wait for vsync
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lda #F_VSYNC
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ldb #IN_FLAGS
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WaitForVsyncOn:
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and none,[B]
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bz WaitForVsyncOn ; wait until VSYNC on
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WaitForVsyncOff:
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and none,[B]
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bnz WaitForVsyncOff ; wait until VSYNC off
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; check collision
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lda #F_COLLIDE
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ldb #IN_FLAGS
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and none,[B] ; collision flag set?
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bz NoCollision ; skip ahead if not
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lda #16
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sta SPEED ; speed = 16
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NoCollision:
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; update speed
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ldb #SPEED
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mov A,[B] ; speed -> A
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inc A ; increment speed
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bz MaxSpeed ; speed wraps to 0?
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sta SPEED ; no, store speed
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MaxSpeed:
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mov A,[B] ; reload speed -> A
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lsr A
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lsr A
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lsr A
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lsr A ; divide speed by 16
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; add to lo byte of track pos
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ldb #TRACKPOS_LO
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add B,[B] ; B <- speed/16 + trackpos_lo
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swapab ; swap A <-> B
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sta TRACKPOS_LO ; A -> trackpos_lo
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swapab ; swap A <-> B again
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bcc NoCarry ; carry flag from earlier add op
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; add to hi byte of track pos
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ldb #TRACKPOS_HI
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mov B,[B] ; B <- trackpos_hi
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inc b ; increment B
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swapab ; swap A <-> B
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sta TRACKPOS_HI ; A -> trackpos_hi
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swapab ; swap A <-> B again
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NoCarry:
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; update enemy vert pos
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ldb #ENEMY_Y
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add A,[B]
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sta ENEMY_Y ; enemy_y = enemy_y + speed/16
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; update enemy horiz pos
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ldb #ENEMY_X
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mov A,[B]
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ldb #ENEMY_DIR
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add A,[B]
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sta ENEMY_X ; enemy_x = enemy_x + enemy_dir
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sub A,#64
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and A,#127 ; A <- (enemy_x-64) & 127
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bnz SkipXReverse ; skip if enemy_x is in range
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; load ENEMY_DIR and negate
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zero A
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sub A,[B]
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sta ENEMY_DIR ; enemy_dir = -enemy_dir
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SkipXReverse:
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; back to display loop
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jmp DisplayLoop
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