mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-06-14 15:29:27 +00:00
45 lines
628 B
NASM
45 lines
628 B
NASM
|
|
;;;;; 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
|
|
|