1 ;; vim: set ft=avr:

     2 ;;

     3 ;; Busy-loop delays

     4 ;;

     5 

     6 ;; Delay for approx. one second

     7 Delay_1s:

     8         ; ~16M cycles

     9         ldi         r20, 82

    10         rjmp        delay_init

    11 

    12 ;; Delay for a variable amount of time, adjusted by r20

    13 ; Input: r20 controls number of delay loops

    14 VarDelay:

    15         tst         r20

    16         breq        delay_out

    17 

    18 delay_init:

    19         ldi         r21, 255

    20 

    21 delay_loop:

    22         ; 254 * (1 + 2) + 1 * (1 + 1) = 764 cycles / loop

    23         dec         r22             

    24         brne        delay_loop

    25 

    26         ; 254 * 764 + 764 = 194820 cycles / loop

    27         dec         r21             ;  1 * r20 * r21

    28         brne        delay_loop      ;  2 * r20 * r21

    29         

    30         ; r20 * 194820 + r20 * 3 = 194823 cycles / loop (r20)

    31         dec         r20             ;  1 * r20 

    32         brne        delay_loop      ;  2 * r20

    33 

    34 delay_out:

    35         ret

    36 

    37