2018-08-13 22:17:36 +00:00
|
|
|
|
2018-08-03 18:06:08 +00:00
|
|
|
;;;;; SUBROUTINES
|
|
|
|
|
|
|
|
|
|
ClearRAM: subroutine
|
|
|
|
|
lda #0
|
|
|
|
|
tax
|
|
|
|
|
.clearRAM
|
|
|
|
|
sta $0,x
|
|
|
|
|
cpx #$fe ; don't clear last 2 bytes of stack
|
|
|
|
|
bcs .skipStack
|
|
|
|
|
sta $100,x
|
|
|
|
|
.skipStack
|
|
|
|
|
; skip $200-$2FF, used for OAM display list
|
|
|
|
|
sta $300,x
|
|
|
|
|
sta $400,x
|
|
|
|
|
sta $500,x
|
|
|
|
|
sta $600,x
|
|
|
|
|
sta $700,x
|
|
|
|
|
inx
|
|
|
|
|
bne .clearRAM
|
|
|
|
|
rts
|
|
|
|
|
|
|
|
|
|
; wait for VSYNC to start
|
|
|
|
|
WaitSync:
|
|
|
|
|
bit PPU_STATUS
|
|
|
|
|
bpl WaitSync
|
|
|
|
|
rts
|
|
|
|
|
|
|
|
|
|
;;;;; RANDOM NUMBERS
|
|
|
|
|
|
|
|
|
|
NextRandom subroutine
|
|
|
|
|
lsr
|
|
|
|
|
bcc .NoEor
|
|
|
|
|
eor #$d4
|
|
|
|
|
.NoEor:
|
|
|
|
|
rts
|
|
|
|
|
; Get previous random value
|
|
|
|
|
PrevRandom subroutine
|
|
|
|
|
asl
|
|
|
|
|
bcc .NoEor
|
|
|
|
|
eor #$a9
|
|
|
|
|
.NoEor:
|
|
|
|
|
rts
|
|
|
|
|
|
2019-02-21 19:19:29 +00:00
|
|
|
;;;;; CONTROLLER READING
|
|
|
|
|
|
|
|
|
|
ReadJoypad subroutine
|
|
|
|
|
lda #$01
|
|
|
|
|
sta JOYPAD1 ; set strobe bit
|
|
|
|
|
tax ; X = 1
|
|
|
|
|
lsr ; now A is 0
|
|
|
|
|
sta JOYPAD1 ; clear strobe bit
|
|
|
|
|
.loop:
|
|
|
|
|
lda JOYPAD1 ; load controller state
|
|
|
|
|
lsr ; bit 0 -> carry
|
|
|
|
|
txa ; X -> A
|
|
|
|
|
rol ; carry -> bit 0 of result, bit 7 -> carry
|
|
|
|
|
tax ; A -> X
|
|
|
|
|
bcc .loop ; repeat until 1 shifted out
|
|
|
|
|
rts ; controller bits returned in A
|
|
|
|
|
|
