.inesprg  1
  .ineschr  1
  .inesmap  0
  .inesmir  1

  .org $0000
AddrLow:    .rs 1
AddrHigh:   .rs 1
nametable:  .rs 1
scroll:     .rs 1
  .bank 0
  .org $C000
;---constants---
sprite_RAM = $0200
controller_RAM = $4016

speed = $01
;---------------

RESET:
  sei
  cld
  ldx #$40
  stx $4017
  ldx #$FF
  txs
  inx
  stx $2000
  stx $2001
  stx $4010

vblankwait1:    ;wait for first vblank to make sure ppu is ready
  bit $2002
  bpl vblankwait1

clrmem:
  lda #$00
  sta $0000, x
  sta $0100, x
  sta $0200, x
  sta $0400, x
  sta $0500, x
  sta $0600, x
  sta $0700, x
  lda #$FE
  sta $0300, x
  inx
  bne clrmem

vblankwait2:    ;ppu is ready after second vblank
  bit $2002
  bpl vblankwait2

;---sprites, controllers---
load_palettes:
  lda $2002
  lda #$3F
  sta $2006
  lda #$00
  sta $2006
  ldx #$00
load_palettes_loop:
  lda palette,x
  sta $2007
  inx
  cpx #$20
  bne load_palettes_loop

load_sprites:
  ldx #$00
load_sprites_loop:
  lda sprite,x
  sta sprite_RAM,x
  inx
  cpx #$20
  bne load_sprites_loop

  lda $2002             ;read PPU to reset latch
  lda #$20
  sta $2006             ; write the high byte of $2000 address (NT 0)
  lda #$00
  sta $2006             ; write the low byte of $2000 address

  lda #low(nametable0)
  sta AddrLow
  lda #high(nametable0)
  sta AddrHigh

  ldy #$00              ;start at background row 0
  ldx #$08

FillNametablesLoop:
  lda [AddrLow],y       ;load data from address
  sta $2007
  iny
  bne FillNametablesLoop
  inc AddrHigh
  dex
  bne FillNametablesLoop

  lda #low(nametable0)
  sta AddrLow
  lda #high(nametable0)
  sta AddrHigh

  ;make PPU render properly next frame
  lda #%10010000    ;enable NMI, sprites from pattern 0, backgrounds from pattern 1
  sta $2000
  lda #%00011110    ;enable sprites, enable background
  sta $2001

;(meta sprite code)

Forever:
  jmp Forever

NMI:
  inc scroll
NTSwapCheck:        ;swap nametables
  lda scroll
  bne NTSwapCheckDone

NTSwap:
  lda nametable
  eor #$01
  sta nametable

NTSwapCheckDone:
  lda #$00
  sta $2003         ;set low byte (00) of ram address
  lda #$02
  sta $4014         ;set high byte (02) of address, start transfer
  ;run other game graphics updating code here
  lda #$00
  sta $2006         ;clean up PPU registers
  sta $2006

  lda scroll
  sta $2005         ;horiz scroll
  lda #$00
  sta $2005         ;no verti scroll

  ;Make PPU render properly next frame
  lda #%10010000    ;enable NMI, sprites from pattern 0, backgrounds from pattern 1
  sta $2000
  lda #%00011110    ;enable sprites, enable background
  sta $2001

;(controller code)

  rti

  .bank 1
  .org $E000
;(pallete, sprite, and background data)

  .org $FFFA
  .dw NMI

  .dw RESET

  .dw 0

  .bank 2
  .org $0000
  .incbin "background.chr"