vader jakob

INESMAP 0
INESPRG 1

seqTimer equ 0
sequenceIdx equ 1

ORG $8000


timerL:
DB $47, $17, $e9, $bf, $96, $70, $4c, $2a, $0a, $ec, $cf, $b4, $9b, $83, $6c, $57, $43, $30, $1e, $0d, $fd, $ee, $df, $d2, $c5
silentL:
DB $01

timerH:
DB $03, $03, $02, $02, $02, $02, $02, $02, $02, $01, $01, $01, $01, $01, $01, $01, $01, $01, $01, $01, $00, $00, $00, $00, $00, $00

silent equ #silentL-timerL

song:
DB 12,14,16,12,12,14,16,12,16,17,19,silent,16,17,19,silent,19,21,19,17,16,silent,12,silent,19,21,19,17,16,silent,12,silent,12,silent,7,silent,12,silent,silent,silent,12,silent,7,silent,12,silent,silent,silent
songLen=$-song

main:
    SEI

;enable pulse channel
    LDA #$01
    STA $4015

;set volume and duty cycle
    LDA #$bf
    STA $4000

;disable sweep
    LDA #$08
    STA $4001

    CLI


end:
    JMP end

IRQ:
;check if frame interrupt
    LDA $4015
    AND #$40
    BEQ ++

;decrement and jump if timer not run out
    DEC seqTimer
    BPL ++

;reset counter
    LDA #$20
    STA seqTimer

;timer action

    LDY sequenceIdx

;check OOB
    LDA #songLen
    CMP sequenceIdx
    BNE +
    LDY #$0

 +  LDX song, y

;get timer value from table
    LDA timerL,x
    STA $4002

    LDA timerH,x
    STA $4003

    INY
    STY sequenceIdx


++  RTI

NMI:
    RTI

PAD $BFFA
DW NMI

PAD $BFFC, $80
DW main

PAD $BFFE
DW IRQ