mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-09-08 06:54:28 +00:00
60 lines
799 B
NASM
60 lines
799 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
|
||
|
|
||
|
; fill video RAM
|
||
|
FillVRAM: subroutine
|
||
|
txa
|
||
|
ldy #$20
|
||
|
sty PPU_ADDR
|
||
|
sta PPU_ADDR
|
||
|
ldy #$10
|
||
|
.loop:
|
||
|
sta PPU_DATA
|
||
|
adc #7
|
||
|
inx
|
||
|
bne .loop
|
||
|
dey
|
||
|
bne .loop
|
||
|
rts
|
||
|
|
||
|
; wait for VSYNC to start
|
||
|
WaitSync:
|
||
|
bit PPU_STATUS
|
||
|
bpl WaitSync
|
||
|
rts
|
||
|
|
||
|
;;;;; RANDOM NUMBERS
|
||
|
|
||
|
NextRandom subroutine
|
||
|
lsr
|
||
|
bcc .NoEor
|
||
|
eor #$d4
|
||
|
.NoEor:
|
||
|
rts
|
||
|
; Get previous random value
|
||
|
PrevRandom subroutine
|
||
|
asl
|
||
|
bcc .NoEor
|
||
|
eor #$a9
|
||
|
.NoEor:
|
||
|
rts
|
||
|
|