/* ----------------------------------------------------------------------
* 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:
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - 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
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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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 */