Dear All,

Recently I needed assembly code for a 16-bit 1:256 FIR low-pass filter.

First I had a look in the PIClist source code library, but I could not find=
 what I needed. I clearly did
not look in the right place, because the code must be there - that's what i=
t says on the tin anyway:
"Huge, really... the code you need is here....".   ;-)

Or perhaps everyone has moved to programming in C ?

Finally, I ended up writing the code myself (see below) and was wondering i=
f a C compiler would
produce the same (or better) code.

Please let me know if the code is worth adding to the PIClist source code l=
ibrary (or where I can
find it).

The code uses the improved instruction set that is available in the "newer"=
 PICs.

Cheers,
Andries

;--------------------------------------------------------------------------=
------------------------------------------------------------
; 1:256 Finite Impuls Response Filter for 16-bit values - Andries Tip 2012
;--------------------------------------------------------------------------=
------------------------------------------------------------

        CBLOCK        h'070'    ; variables available from any bank

        setpoint1               ; setpoint is the 16-bit input value
        setpoint2               ;

        average0                ; average2:average1 is the filtered output =
value
        average1                ; average0 is the fractional part
        average2                ;

        temp                    ; temporary value used in calculation

        ENDC

;--------------------------------------------------------------------------=
------------------------------------------------------------

FIR_256_16BIT                                 ; average =3D (255*average + =
setpoint)/256

                movf        average0,w        ; average =3D 256*average - a=
verage =3D 255*average
                sublw       d'0'              ; prepare carry
                movwf       temp              ; save value for rounding lat=
er, otherwise we cannot reach 65535
                movf        average1,w        ;
                subwfb      average0,f        ;
                movf        average2,w        ;
                subwfb      average1,f        ;
                movlw       d'0'              ;
                subwfb      average2,f        ;

                movlw       d'255'            ; average =3D round((average =
+ setpoint)/256)
                addwf       temp,w            ;
                movf        setpoint1,w       ;
                addwfc      average0,f        ;
                movf        setpoint2,w       ;
                addwfc      average1,f        ;
                clrw                          ;
                addwfc      average2,f        ;


;--------------------------------------------------------------------------=
------------------------------------------------------------
--=20
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