;*****************************************************************
;* This stationery serves as the framework for a                 *
;* user application (single file, absolute assembly application) *
;* For a more comprehensive program that                         *
;* demonstrates the more advanced functionality of this          *
;* processor, please see the demonstration applications          *
;* located in the examples subdirectory of the                   *
;* Freescale CodeWarrior for the HC12 Program directory          *
;*****************************************************************

; export symbols
            XDEF Entry, _Startup            ; export 'Entry' symbol
            ABSENTRY Entry        ; for absolute assembly: mark this as application entry point


; Include derivative-specific definitions 
		INCLUDE 'derivative.inc' 

ROMStart    EQU  $4000  ; absolute address to place my code/constant data

; variable/data section

            ORG RAMStart ; Start data at $1000
 ; Insert here your data definition.
Counter     DC.W 10 ; Fibonacci number to compute: Fibonacci(10), must be greater or equal than 1
FiboRes     DS.W 1  ; 1 word (16 bits) reserved for the result


; code section
            ORG   ROMStart


Entry:
_Startup:   LDS   #RAMEnd+1       ; initialize the stack pointer. SP <- $3FFF+1

mainLoop:   LDX   Counter         ; X contains counter
            CPX   #24
            bhi   mainLoop       ; larger values than 24 cause overflow!

            BSR   CalcFibo
            STD   FiboRes         ; store result
            BRA   mainLoop        ; restart.


; ====================================================================
; Subroutines
; ====================================================================
CalcFibo:  ; Function to calculate fibonacci numbers. Argument is in X.
            pshx
            LDY   #$00            ; second last
            LDD   #$01            ; last
            DBEQ  X,FiboDone      ; loop once more (if X was 1, were done already)
FiboLoop:
            LEAY  D,Y             ; overwrite second last with new value
            EXG   D,Y             ; exchange them -> order is correct again
            DBNE  X,FiboLoop
FiboDone:   pulx
            RTS                   ; result in D