irq.asm

;============================================================
;    some initialization and interrupt redirect setup
;============================================================

           sei         ; set interrupt disable flag
            
           jsr init_screen     ; clear the screen
           jsr init_text       ; write lines of text
           jsr sid_init     ; init music routine now

           ldy #$7f    ; $7f = %01111111
           sty $dc0d   ; Turn off CIAs Timer interrupts
           sty $dd0d   ; Turn off CIAs Timer interrupts
           lda $dc0d   ; cancel all CIA-IRQs in queue/unprocessed
           lda $dd0d   ; cancel all CIA-IRQs in queue/unprocessed
          
           lda #$01    ; Set Interrupt Request Mask...
           sta $d01a   ; ...we want IRQ by Rasterbeam

           lda #<irq   ; point IRQ Vector to our custom irq routine
           ldx #>irq 
           sta $314    ; store in $314/$315
           stx $315   

           lda #$00    ; trigger first interrupt at row zero
           sta $d012

           lda $d011   ; Bit#0 of $d011 is basically...
           and #$7f    ; ...the 9th Bit for $d012
           sta $d011   ; we need to make sure it is set to zero 

           cli         ; clear interrupt disable flag
           jmp *       ; infinite loop


;============================================================
;    custom interrupt routine
;============================================================

irq        dec $d019        ; acknowledge IRQ

           jsr colwash      ; jump to color cycling routine
           jsr play_music   ; jump to play music routine


           jmp $ea81        ; return to kernel interrupt routine