NewButtons = $c1
OldButtons = $c2
JustPressed = $c3

SongNumber = $c4
OldSong = $c5

LoadAddy = $90E1
InitAddy = $AC00
PlayAddy = $AC03

;       ----------------------------------------------------

        .ORG $7ff0
Header:                         ; 16 byte .NES header (iNES format)
    .DB "NES", $1a
    .DB $02                 ; size of PRG ROM in 16kb units
    .DB $01         ; size of CHR ROM in 8kb units
    .DB #%00000000      ; mapper 0
    .DB #%00000000      ; mapper 0
        .DB $00
        .DB $00
        .DB $00
        .DB $00
        .DB $00
        .DB $00
        .DB $00
        .DB $00

;       ----------------------------------------------------

        .org LoadAddy
        .incbin "mm5.nsf"      ; NSF filename

        .org $fa00              ; start of code

;       ----------------------------------------------------

Reset:                          ; reset routine
        SEI
        CLD
    LDX #$00
    STX $2000
    STX $2001
    DEX
    TXS
    LDX #0
    TXA
ClearMemory:
    STA 0, X
    STA $100, X
    STA $200, X
    STA $300, X
    STA $400, X
    STA $500, X
    STA $600, X
    STA $700, X
        STA $800, X
        STA $900, X
        INX
    BNE ClearMemory

;       ----------------------------------------------------

    LDX #$02                ; warm up
WarmUp:
    BIT $2002
    BPL WarmUp
    DEX
    BNE WarmUp

        LDA #$3F
    STA $2006
    LDA #$00
    STA $2006
        TAX
LoadPal:                        ; load palette
        LDA palette, x
        STA $2007
        INX
        CPX #$20
        BNE LoadPal

    LDA #$20
    STA $2006
    LDA #$00
    STA $2006

    LDY #$04                ; clear nametables
ClearName:
    LDX #$00
    LDA #$00
PPULoop:
    STA $2007
    DEX
    BNE PPULoop

    DEY
    BNE ClearName

;       ----------------------------------------------------

        LDA #$00                ; set up variables
        STA SongNumber
        LDA #$00
        STA Play

;       ----------------------------------------------------

        JSR DrawScreen          ; draw initial nametable
        JSR InitSprites
        JSR InitMusic
        JSR Vblank              ; turn on screen

;       ----------------------------------------------------

InfLoop:                        ; loop forever, program now controlled by NMI routine

        JMP InfLoop

;       ----------------------------------------------------

InitMusic:

    lda #$00
    ldx #$00
Clear_Sound:
    sta $4000,x
    inx
    cpx #$0F
    bne Clear_Sound

    lda #$10
    sta $4010
    lda #$00
    sta $4011
    sta $4012
    STA $4013

    lda #%00001111
    STA $4015

    lda #$C0
    STA $4017

    LDA SongNumber      ; song number
    ldx #$00        ; 00 for NTSC or $01 for PAL
    jsr InitAddy        ; init address
    rts

;       ----------------------------------------------------

DrawScreen:

        LDA #<pic              ; load low byte of first picture
        STA $10
        LDA #>pic              ; load high byte of first picture
        STA $11

    LDA #$20                ; set to beginning of first nametable
        STA $2006
        LDA #$00
        STA $2006

        LDY #$00
        LDX #$04

NameLoop:                       ; loop to draw entire nametable
        LDA ($10),y
        STA $2007
        INY
        BNE NameLoop
        INC $11
        DEX
        BNE NameLoop

        RTS

;       ----------------------------------------------------

InitSprites:
      LDA #$ff
      LDX #$00
ClearSprites:
      STA $500, x
      INX
      BNE ClearSprites

      LDA #$00
      STA $2003                 ; set the low byte (00) of the RAM address
      LDA #$05
      STA $4014                 ; set the high byte (05) of the RAM address

LoadSprites:
      LDX #$00
LoadSpritesLoop:
      LDA sprites, x            ; load data from address
      STA $0500, x              ; store into RAM address
      INX
      CPX #4
      BNE LoadSpritesLoop
      RTS

sprites:
           ;vert tile attr horiz
        .db $37, $2D, $00, $17  ; sprite

;       ----------------------------------------------------

UpdateSprites:
        LDA #$00
        STA $2003
        LDA #$05
        STA $4014
        RTS

;       ----------------------------------------------------

ChangeSprite:
        LDX SongNumber
        LDA Line,x
        STA $0500
        RTS

Line:
        .db $37,$47,$57,$67,$77,$87,$97,$A7,$B7,$C7

;       ----------------------------------------------------

Vblank:                         ; turn on the screen and start the party
    BIT $2002
    BPL Vblank

        LDX #$00
        STX $2005
        STX $2005

    LDA #%10001000
    STA $2000
        LDA #%00011110
    STA $2001

        RTS

;       ----------------------------------------------------

ControllerTest:

        LDA NewButtons
    STA OldButtons

        LDX #$00
    LDA #$01        ; strobe joypad
    STA $4016
    LDA #$00
    STA $4016
ConLoop:
    LDA $4016       ; check the state of each button
    LSR
    ROR NewButtons
        INX
        CPX #$08
        bne ConLoop

    LDA OldButtons          ; invert bits
    EOR #$FF
    AND NewButtons
    STA JustPressed

    LDA SongNumber          ; save old song number for later compare
    STA OldSong

CheckA:
    LDA #%00000001
    AND JustPressed
    BEQ CheckDown


CheckDown:
    LDA #%00100000
    AND JustPressed
    BEQ CheckUp

    INC SongNumber          ; increment song number here
        LDA SongNumber
    CMP #2                  ; equal to total # of songs +1, starting from 0
    BNE CheckUp
    LDA #0
    STA SongNumber

CheckUp:
    LDA #%00010000
    AND JustPressed
    BEQ EndDrawChk

        DEC SongNumber          ; decrement song number here
        BPL EndDrawChk
    LDA #1                  ; equal to total # of songs, starting from 0
    STA SongNumber

EndDrawChk:
    LDA SongNumber          ; has song number changed? if so, load next song
    CMP OldSong
    BEQ CheckOver
    JSR ChangeSprite
        JSR InitMusic

CheckOver:

        RTS

;       ----------------------------------------------------

NMI:
        JSR UpdateSprites
        JSR ControllerTest      ; check for user input
        IF Play>0
            jsr PlayAddy        ; init address
            RTI
        ELSE
            RTI
        ENDIF


        ;jsr PlayAddy            ; play the music

        ;RTI
IRQ:
        RTI

;       ----------------------------------------------------

palette:                        ; palette data
        .byte $0F,$10,$20,$30,$0F,$10,$20,$30,$0F,$10,$20,$30,$0F,$10,$20,$30
        .byte $0F,$10,$20,$30,$0F,$10,$20,$30,$0F,$10,$20,$30,$0F,$10,$20,$30

;       ----------------------------------------------------

pic:
        .INCBIN "screen.nam"

;       ----------------------------------------------------

    .ORG $fffa              ; vectors
    .DW NMI
    .DW Reset
    .DW IRQ