FIR Filter Library
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FIR Filter Library

mikroPascal PRO for dsPIC30/33 and PIC24 includes a library for finite impulse response (FIR) filter. All routines work with fractional Q15 format.

A finite impulse response (FIR) filter is a type of a digital filter, whose impulse response (the filter's response to a delta function) is finite because it settles to zero in a finite number of sample intervals.

Library Routines

FIR_Radix

Prototype

function FIR_Radix(FilterOrder: word; ptrCoeffs: longint; BuffLength: word; ptrInput: word; Index: word): word;
Description

This function applies FIR filter to ptrInput.
Parameters
  • FilterOrder: order of the filter + 1
  • ptrCoeffs: address of filter coefficients in program memory
  • BuffLength number of input samples
  • ptrInput: address of input samples
  • Index: index of current sample
Returns

with :
N - buffer length
k - current index
Requires

Nothing.
Example 
const BUFFFER_SIZE = 32;
const FILTER_ORDER = 20;   
const COEFF_B[FILTER_ORDER+1] of integer = (
      0x0000, 0x0048, 0x0133, 0x02D3, 0x052B, 0x0826,
      0x0BA0, 0x0F62, 0x1329, 0x16AA, 0x199A, 0x16AA,
      0x1329, 0x0F62, 0x0BA0, 0x0826, 0x052B, 0x02D3,
      0x0133, 0x0048, 0x0000
);

var input: array[BUFFFER_SIZE] of word; ydata;   // Input buffer
  inext: word;                                   // Input buffer index
...
var CurrentValue: word;
CurrentValue := FIR_Radix(FILTER_ORDER+1,  // Filter order
                          word(@COEFF_B),  // B coefficients of the filter
                          BUFFFER_SIZE,    // Input buffer length
                          word(@input),    // Input buffer
                          inext);          // Current sample
Notes

Input samples must be in Y data space.
Copyright (c) 2002-2012 mikroElektronika. All rights reserved.
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