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/* ----------------------------------------------------------------------

 * 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

* are met:

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*   - Redistributions in binary form must reproduce the above copyright

*     notice, this list of conditions and the following disclaimer in

*     the documentation and/or other materials provided with the

*     distribution.

*   - Neither the name of ARM LIMITED nor the names of its contributors

*     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 */