Burn Time

; Simple loop to burn time in a program
; Syntax used is for ca65

; The three bytes needed in RAM
nmi_wait:   .res 1
one_second: .res 1
big_seconds:    .res 1

; The routine nmi_wait
nmi_wait:
    lda nmi_num
:   cmp nmi_num
    beq :-
    rts

; Must have one_second and big_seconds already setup.
; Use #$3c in one_second to wait 60 frames
; Use the number of seconds you want to use in big_seconds
loop:
    lda one_second          ; Subtract one_second by one
    sec                             ;  and if it's not zero, branch
    sbc #$01            ;  over
    sta one_second          ;
    bne @end            ;
        lda #$3c        ; When one_second reaches zero,
        sta one_second      ;  reset it to #$3c and subtract
        lda big_seconds     ;  big_seconds by one. Test if
        sec         ;  big_seconds is zero. If not,
        sbc #$01        ;  we wait for another NMI and
        sta big_seconds     ;  start the loop over. If zero,
        bne @end        ;  jmp over the nmi_wait...
            jmp @finally    ;
@end:                   ;
    jsr nmi_wait            ;
    jmp loop            ;
@finally:               ; Here we begin setup for the next
                    ;  loop in the program