FIR Filter Library
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FIR Filter Library

mikroBasic 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

sub function FIR_Radix(dim ptrCoeffs as ^const q15, dim FilterOrder as word, dim ptrInput as ^q15, dim InputLength as word, dim Index as word) as q15
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

program FIR

dim   FILTER_ORDER  as word
      inputSamples  as integer[3]
      outputSamples as integer[6]
      i             as word
const COEFF_B       as integer[4] = (0x0000, 0x1255, 0x1255, 0x0000)

sub procedure Init()

  inputSamples[0] = 0x4000
  inputSamples[1] = 0x2000
  inputSamples[2] = 0x1000
  FILTER_ORDER = 3
  end sub

main:
  Init()
  for i= 0 to 5
    outputSamples[i] = FIR_Radix(@COEFF_B, FILTER_ORDER+1, @inputSamples, 3,  i)
  next i
  asm nop end asm
  ' 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]

end.
Notes

None.
Copyright (c) 2002-2012 mikroElektronika. All rights reserved.
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