Scott Dattalo wrote:
>
> Ralf Sigmund wrote:
>
> > So I would like to implement a running average algorithm, which gives
> > the average of the last eight values.
> > It should add up the last eight values and divide then by 8.
> > but my values can be everything between 256 and 0.



y = ( a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 ) / 8

    ( ( ( a1 + a2 )/2 + ( a3 + a4 )/2 )/2 + ( ( a5 + a6 )/2 + ( a7 + a8
)/2 )/2 )/2

It will be more easy if your values will range from 0 to 255 ( byte
value )



> Ralf,
>
> Is it necessary to average the last 8 values non-recursively?
> In other words, you're proposing a low-pass digital FIR (finite
> impulse response) filter. The frequency response is "okay", but...
> Have you considered an IIR (infinite impulse response) filter?
> Specifically, I've had good results with filters of this type:
>
>    avg = (m*avg + n*sample) /(m+n)
>
> e.g. If I wish to give the average more weight than the current sample:
>    avg = (3*avg + sample)/4
> Or, vice-versa:
>    avg = (avg + 3*sample)/4
>
> An example of the later case implemented in ASM (and untested):
>
>         CLRF    temp
>         CLRC
>         RLF     sample,W   ;W = 2*sample
>         RLF     temp,F     ;Catch the carry
>         ADDWF   sample,W   ;W = 3*sample
>         SKPNC
>          INCF   temp,F     ;Catch the carry again
>         ADDWF   avg,F      ;avg = avg+3*sample
>         SKPNC
>          INCF   temp,F
>         RRF     temp,F     ;Get the carries
>         RRF     avg,F      ;avg /= 2
>         RRF     temp,F
>         RRF     avg,F      ;avg /= 4
>
> 14 Cycles
>
> Scott

There are more short version algorithm above ;) No additional cell
required

avg = (avg + 3*sample)/4 = ( ( avg + sample )/2 + sample )/2

        MOVFW   SAMPLE
        ADDWF   AVG,F
        RRF     AVG,F
        ADDWF   AVG,F
        RRF     AVG,F

5 Cycles

WBR Dmitry.