arm_fir_example_f32.c

/* ----------------------------------------------------------------------
 * Copyright (C) 2010-2012 ARM Limited. All rights reserved.
 *
* $Date:         17. January 2013
* $Revision:     V1.4.0
*
* Project:       CMSIS DSP Library
 * Title:        arm_fir_example_f32.c
 *
 * Description:  Example code demonstrating how an FIR filter can be used
 *               as a low pass filter.
 *
 * Target Processor: Cortex-M4/Cortex-M3
 *
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
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*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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/**
 * @ingroup groupExamples
 */

/**
 * @defgroup FIRLPF FIR Lowpass Filter Example
 *
 * \par Description:
 * \par
 * Removes high frequency signal components from the input using an FIR lowpass filter.
 * The example demonstrates how to configure an FIR filter and then pass data through
 * it in a block-by-block fashion.
 * \image html FIRLPF_signalflow.gif
 *
 * \par Algorithm:
 * \par
 * The input signal is a sum of two sine waves:  1 kHz and 15 kHz.
 * This is processed by an FIR lowpass filter with cutoff frequency 6 kHz.
 * The lowpass filter eliminates the 15 kHz signal leaving only the 1 kHz sine wave at the output.
 * \par
 * The lowpass filter was designed using MATLAB with a sample rate of 48 kHz and
 * a length of 29 points.
 * The MATLAB code to generate the filter coefficients is shown below:
 * <pre>
 *     h = fir1(28, 6/24);
 * </pre>
 * The first argument is the "order" of the filter and is always one less than the desired length.
 * The second argument is the normalized cutoff frequency.  This is in the range 0 (DC) to 1.0 (Nyquist).
 * A 6 kHz cutoff with a Nyquist frequency of 24 kHz lies at a normalized frequency of 6/24 = 0.25.
 * The CMSIS FIR filter function requires the coefficients to be in time reversed order.
 * <pre>
 *     fliplr(h)
 * </pre>
 * The resulting filter coefficients and are shown below.
 * Note that the filter is symmetric (a property of linear phase FIR filters)
 * and the point of symmetry is sample 14.  Thus the filter will have a delay of
 * 14 samples for all frequencies.
 * \par
 * \image html FIRLPF_coeffs.gif
 * \par
 * The frequency response of the filter is shown next.
 * The passband gain of the filter is 1.0 and it reaches 0.5 at the cutoff frequency 6 kHz.
 * \par
 * \image html FIRLPF_response.gif
 * \par
 * The input signal is shown below.
 * The left hand side shows the signal in the time domain while the right hand side is a frequency domain representation.
 * The two sine wave components can be clearly seen.
 * \par
 * \image html FIRLPF_input.gif
 * \par
 * The output of the filter is shown below.  The 15 kHz component has been eliminated.
 * \par
 * \image html FIRLPF_output.gif
 *
 * \par Variables Description:
 * \par
 * \li \c testInput_f32_1kHz_15kHz points to the input data
 * \li \c refOutput points to the reference output data
 * \li \c testOutput points to the test output data
 * \li \c firStateF32 points to state buffer
 * \li \c firCoeffs32 points to coefficient buffer
 * \li \c blockSize number of samples processed at a time
 * \li \c numBlocks number of frames
 *
 * \par CMSIS DSP Software Library Functions Used:
 * \par
 * - arm_fir_init_f32()
 * - arm_fir_f32()
 *
 * <b> Refer  </b>
 * \link arm_fir_example_f32.c \endlink
 *
 */


/** \example arm_fir_example_f32.c
 */

/* ----------------------------------------------------------------------
** Include Files
** ------------------------------------------------------------------- */

#include "arm_math.h"
#include "math_helper.h"

/* ----------------------------------------------------------------------
** Macro Defines
** ------------------------------------------------------------------- */

#define TEST_LENGTH_SAMPLES  320
#define SNR_THRESHOLD_F32    140.0f
#define BLOCK_SIZE            32
#define NUM_TAPS              29

/* -------------------------------------------------------------------
 * The input signal and reference output (computed with MATLAB)
 * are defined externally in arm_fir_lpf_data.c.
 * ------------------------------------------------------------------- */

extern float32_t testInput_f32_1kHz_15kHz[TEST_LENGTH_SAMPLES];
extern float32_t refOutput[TEST_LENGTH_SAMPLES];

/* -------------------------------------------------------------------
 * Declare Test output buffer
 * ------------------------------------------------------------------- */

static float32_t testOutput[TEST_LENGTH_SAMPLES];

/* -------------------------------------------------------------------
 * Declare State buffer of size (numTaps + blockSize - 1)
 * ------------------------------------------------------------------- */

static float32_t firStateF32[BLOCK_SIZE + NUM_TAPS - 1];

/* ----------------------------------------------------------------------
** FIR Coefficients buffer generated using fir1() MATLAB function.
** fir1(28, 6/24)
** ------------------------------------------------------------------- */

const float32_t firCoeffs32[NUM_TAPS] = {
  -0.0018225230f, -0.0015879294f, +0.0000000000f, +0.0036977508f, +0.0080754303f, +0.0085302217f, -0.0000000000f, -0.0173976984f,
  -0.0341458607f, -0.0333591565f, +0.0000000000f, +0.0676308395f, +0.1522061835f, +0.2229246956f, +0.2504960933f, +0.2229246956f,
  +0.1522061835f, +0.0676308395f, +0.0000000000f, -0.0333591565f, -0.0341458607f, -0.0173976984f, -0.0000000000f, +0.0085302217f,
  +0.0080754303f, +0.0036977508f, +0.0000000000f, -0.0015879294f, -0.0018225230f
};

/* ------------------------------------------------------------------
 * Global variables for FIR LPF Example
 * ------------------------------------------------------------------- */

uint32_t blockSize = BLOCK_SIZE;
uint32_t numBlocks = TEST_LENGTH_SAMPLES/BLOCK_SIZE;

float32_t  snr;

/* ----------------------------------------------------------------------
 * FIR LPF Example
 * ------------------------------------------------------------------- */

int32_t main(void)
{
  uint32_t i;
  arm_fir_instance_f32 S;
  arm_status status;
  float32_t  *inputF32, *outputF32;

  /* Initialize input and output buffer pointers */
  inputF32 = &testInput_f32_1kHz_15kHz[0];
  outputF32 = &testOutput[0];

  /* Call FIR init function to initialize the instance structure. */
  arm_fir_init_f32(&S, NUM_TAPS, (float32_t *)&firCoeffs32[0], &firStateF32[0], blockSize);

  /* ----------------------------------------------------------------------
  ** Call the FIR process function for every blockSize samples
  ** ------------------------------------------------------------------- */

  for(i=0; i < numBlocks; i++)
  {
    arm_fir_f32(&S, inputF32 + (i * blockSize), outputF32 + (i * blockSize), blockSize);
  }

  /* ----------------------------------------------------------------------
  ** Compare the generated output against the reference output computed
  ** in MATLAB.
  ** ------------------------------------------------------------------- */

  snr = arm_snr_f32(&refOutput[0], &testOutput[0], TEST_LENGTH_SAMPLES);

  if (snr < SNR_THRESHOLD_F32)
  {
    status = ARM_MATH_TEST_FAILURE;
  }
  else
  {
    status = ARM_MATH_SUCCESS;
  }

  /* ----------------------------------------------------------------------
  ** Loop here if the signal does not match the reference output.
  ** ------------------------------------------------------------------- */

  if( status != ARM_MATH_SUCCESS)
  {
    while(1);
  }

  while(1);                             /* main function does not return */
}

/** \endlink */