FIR Filter Library
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FIR Filter Library

mikroC PRO for PIC32 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

int FIR_Radix(const int *ptrCoeffs, unsigned FilterOrder, int *ptrInput, unsigned InputLength, unsigned Index);
Description

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

Function returns value of the Index-th sample of the filtered signal :



with :
N - filter order
k - current index
Requires

Nothing.
Example 
// Filter setup:
//     Filter kind: FIR
//     Filter type: Lowpass filter
//     Filter order: 3
//     Filter window: Blackman
//     Filter borders:
//       Wpass:4000 Hz
const unsigned FILTER_ORDER  = 3;

const int COEFF_B[FILTER_ORDER+1] = {
      0x0000, 0x1255, 0x1255, 0x0000};
int   inputSamples[3] = {0x4000, 0x2000, 0x1000};
int   outputSamples[6];
unsigned i;
      
void main() {
  for (i = 0; i < 6; i++)
    outputSamples[i] = FIR_Radix(COEFF_B, FILTER_ORDER+1, inputSamples, 3,  i);

  // outputSamples[0] = COEFF_B[0]*inputSamples[0];
  // outputSamples[1] = COEFF_B[0]*inputSamples[1] + COEFF_B[1]*inputSamples[0];
  // outputSamples[2] = COEFF_B[0]*inputSamples[2] + COEFF_B[1]*inputSamples[1] + COEFF_B[2]*inputSamples[0];
  // .
  // .
  // .
}
Notes

None.
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