# Pastebin Dh4TWmw4
; Check the handler's non-null, if so call it.
.macro _check_handler maskAddr, maskBit, next
    lda $DC
    sta $E420

    lda maskAddr
    sta irq_mask_tmp

    bbr maskBit, irq_mask_tmp, next
.endmacro

.macro _call_handler_once handler, maskAddr, maskBit
    lda #$DE
    sta $E420

    lda maskAddr
    sta irq_mask_tmp

    rmb maskBit, maskAddr

    lda irq_mask_tmp
    sta maskAddr
    
    jsr handler
.endmacro