44 lines
2.3 KiB
PHP
44 lines
2.3 KiB
PHP
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||
|
|
;; Macro to initialize the NES by disabling rendering and clearing RAM values
|
||
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||
|
|
.macro INIT_NES
|
||
|
|
sei ; Disable all IRQ interrupts
|
||
|
|
cld ; Clear decimal mode (not supported by the NES)
|
||
|
|
ldx #$FF
|
||
|
|
txs ; Initialize the stack pointer at address $FF
|
||
|
|
|
||
|
|
inx ; Increment X, causing a rolloff from $FF to $00
|
||
|
|
stx PPU_CTRL ; Disable NMI
|
||
|
|
stx PPU_MASK ; Disable rendering (masking background and sprites)
|
||
|
|
stx $4010 ; Disable DMC IRQs
|
||
|
|
|
||
|
|
lda #$40
|
||
|
|
sta $4017 ; Disable APU frame IRQ
|
||
|
|
|
||
|
|
bit PPU_STATUS ; Read from PPU_STATUS to reset the VBlank flag
|
||
|
|
Wait1stVBlank: ; Wait for the first VBlank from the PPU
|
||
|
|
bit PPU_STATUS ; Perform a bit-wise check with the PPU_STATUS port
|
||
|
|
bpl Wait1stVBlank ; Loop until bit-7 (sign bit) is 1 (inside VBlank)
|
||
|
|
|
||
|
|
txa ; A = 0
|
||
|
|
ClearRAM:
|
||
|
|
sta $0000,x ; Zero RAM addresses from $0000 to $00FF
|
||
|
|
sta $0100,x ; Zero RAM addresses from $0100 to $01FF
|
||
|
|
|
||
|
|
lda #$FF ; We init OAM data with $FF to hide sprites
|
||
|
|
sta $0200,x ; Zero RAM addresses from $0200 to $02FF with $FF
|
||
|
|
lda #0
|
||
|
|
|
||
|
|
sta $0300,x ; Zero RAM addresses from $0300 to $03FF
|
||
|
|
sta $0400,x ; Zero RAM addresses from $0400 to $04FF
|
||
|
|
sta $0500,x ; Zero RAM addresses from $0500 to $05FF
|
||
|
|
sta $0600,x ; Zero RAM addresses from $0600 to $06FF
|
||
|
|
sta $0700,x ; Zero RAM addresses from $0700 to $07FF
|
||
|
|
inx
|
||
|
|
bne ClearRAM
|
||
|
|
|
||
|
|
Wait2ndVBlank: ; Wait for the second VBlank from the PPU
|
||
|
|
bit PPU_STATUS ; Perform a bit-wise check with the PPU_STATUS port
|
||
|
|
bpl Wait2ndVBlank ; Loop until bit-7 (sign bit) is 1 (inside VBlank)
|
||
|
|
.endmacro
|