.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
    stx $4010                ; disable DMC IRQs

    lda #$40
    sta $4017                ; disable APU frame IRQ

Wait1stVBlank:
    bit PPU_STATUS
    bpl Wait1stVBlank

    txa                      ; A = 0

ClearRAM:
    sta $0000,x              ; Zero RAM addresses from $0000 to $00FF
    sta $0100,x              ; Zero RAM addresses from $0100 to $01FF
    sta $0200,x              ; Zero RAM addresses from $0200 to $02FF
    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:
    bit PPU_STATUS
    bpl Wait2ndVBlank        ; bit-7 is 1


.endmacro