So, I’m very new to assembly language programming for microcontrollers.

I’m using an AVR XMega A3BU X-plained board, and I’ve got a program where I need to interface with 7 buttons. 3 of them are on the board, and 4 are connected to a cheap 4 button membrane keypad.

I need to debounce the switches (hardware solutions are not an option), and I’ve constructed the following routine to do it; I feel like it’s horribly inefficient and has several design flaws, but I can’t tell.

(The CPU clock is running at 32 MHz and the timer interrupt occurs every 100ms.)

C programming is not an option, I must use assembly.

Is there a better way to do this?

;------------------------------------------------------------------------------ ; Timer interrupt service routine - tcf0_isr ;------------------------------------------------------------------------------ ; TODO - document this routine ;------------------------------------------------------------------------------ .equ        DEBOUNCE_VALUE   =0xFF                   ;  tcf0_isr:                                       ;             push        r16                     ; check_ib1:                                      ;             lds         r16,PORTE_IN            ;             sbrs        r16,5                   ; if(ib1 is down)             rjmp        ib1_is_down             ;   debounce ib1             clr         r16                     ; else reset debounce counter             sts         ib1downcnt,r16          ;       *             jmp         check_ib2               ;       * ib1_is_down:                                    ;             lds         r16,ib1downcnt          ; Debounce ib1             inc         r16                     ;       *             sts         ib1downcnt,r16          ;       *             cpi         r16,DEBOUNCE_VALUE      ;       *             breq        ib1_debounced           ;       * ib1_debounced:                                  ;       *             call        sel_wng_pressed         ; Call ib1 handling routine check_ib2:                                      ; Check 2nd button on board             ; todo check_ib3:                                      ; Check 3rd button on board             ; and so on check_eb1:                                      ; Check 1st external button             ; and so on check_eb2:                                      ; Check 2nd external button  check_eb3:                                      ; Check 3rd external button  check_eb4:                                      ; Check 4th external button             pop         r16                     ;             reti                                ; ;------------------------------------------------------------------------------