filter_applications EQU (end_source-source)/4 - 5	; find out how many times the filter needs to be applied

  AREA Filter_Code, CODE, READONLY
Reset_Handler
  ENTRY
  ; set up the filter parameters
  LDR r0,=source
  LDR r3,=dest
  MOVS r4,#filter_applications
  BMI exit


filter_loop
  LDMIA r0,{r5-r9}    ; get the next 5 data values to be filtered
  ADD r5,r5,r9         ; sum x[-2] with x[2]
  ADD r6,r6,r8         ; sum x[-1] with x[1]
  ADD r9,r5,r6         ; sum x[-2]+x[2] with x[-1]+x[1]
  ADD r7,r7,r9,LSR #1  ; sum x[0] with (x[-2]+x[2]+x[-1]+x[1])/2
  MOV r7,r7,LSR #2     ; form (x[0] + (x[-2]+x[-1]+x[1]+x[2])/2)/4
  STR r7,[r3],#4       ; save calculated filtered value, move to next output data item
  ADD r0,r0,#4         ; move on to next set of 5 inputs
  SUBS r4,r4,#1        ; move on to next set of 5 inputs
  BPL filter_loop      ; continue until last set of 5 inputs reached


exit
  B exit

 ALIGN
  AREA Filter_ROData, DATA, READONLY
source  ; example saw tooth
  DCD 0,10,20,30,40,50,60,70,80,90,100,0,10,20,30,40,50,60,70,80,90,100
  DCD 0,10,20,30,40,50,60,70,80,90,100,0,10,20,30,40,50,60,70,80,90,100
  DCD 0,10,20,30,40,50,60,70,80,90,100,0,10,20,30,40,50,60,70,80,90,100
  DCD 0,10,20,30,40,50,60,70,80,90,100,0,10,20,30,40,50,60,70,80,90,100

  AREA Filter_RWData, DATA, READWRITE
dest
  SPACE end_source - source - 16
end_dest
  END