/* ----------------------------------------------------------------------
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* Copyright (C) 2010-2012 ARM Limited. All rights reserved.
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*
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* $Date: 17. January 2013
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* $Revision: V1.4.0
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*
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* Project: CMSIS DSP Library
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* Title: arm_fir_example_f32.c
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*
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* Description: Example code demonstrating how an FIR filter can be used
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* as a low pass filter.
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*
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* Target Processor: Cortex-M4/Cortex-M3
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* - Neither the name of ARM LIMITED nor the names of its contributors
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* may be used to endorse or promote products derived from this
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* software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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* -------------------------------------------------------------------- */
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/**
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* @ingroup groupExamples
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*/
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/**
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* @defgroup FIRLPF FIR Lowpass Filter Example
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*
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* \par Description:
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* \par
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* Removes high frequency signal components from the input using an FIR lowpass filter.
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* The example demonstrates how to configure an FIR filter and then pass data through
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* it in a block-by-block fashion.
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* \image html FIRLPF_signalflow.gif
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*
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* \par Algorithm:
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* \par
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* The input signal is a sum of two sine waves: 1 kHz and 15 kHz.
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* This is processed by an FIR lowpass filter with cutoff frequency 6 kHz.
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* The lowpass filter eliminates the 15 kHz signal leaving only the 1 kHz sine wave at the output.
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* \par
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* The lowpass filter was designed using MATLAB with a sample rate of 48 kHz and
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* a length of 29 points.
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* The MATLAB code to generate the filter coefficients is shown below:
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* <pre>
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* h = fir1(28, 6/24);
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* </pre>
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* The first argument is the "order" of the filter and is always one less than the desired length.
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* The second argument is the normalized cutoff frequency. This is in the range 0 (DC) to 1.0 (Nyquist).
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* A 6 kHz cutoff with a Nyquist frequency of 24 kHz lies at a normalized frequency of 6/24 = 0.25.
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* The CMSIS FIR filter function requires the coefficients to be in time reversed order.
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* <pre>
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* fliplr(h)
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* </pre>
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* The resulting filter coefficients and are shown below.
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* Note that the filter is symmetric (a property of linear phase FIR filters)
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* and the point of symmetry is sample 14. Thus the filter will have a delay of
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* 14 samples for all frequencies.
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* \par
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* \image html FIRLPF_coeffs.gif
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* \par
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* The frequency response of the filter is shown next.
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* The passband gain of the filter is 1.0 and it reaches 0.5 at the cutoff frequency 6 kHz.
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* \par
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* \image html FIRLPF_response.gif
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* \par
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* The input signal is shown below.
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* The left hand side shows the signal in the time domain while the right hand side is a frequency domain representation.
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* The two sine wave components can be clearly seen.
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* \par
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* \image html FIRLPF_input.gif
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* \par
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* The output of the filter is shown below. The 15 kHz component has been eliminated.
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* \par
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* \image html FIRLPF_output.gif
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*
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* \par Variables Description:
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* \par
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* \li \c testInput_f32_1kHz_15kHz points to the input data
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* \li \c refOutput points to the reference output data
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* \li \c testOutput points to the test output data
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* \li \c firStateF32 points to state buffer
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* \li \c firCoeffs32 points to coefficient buffer
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* \li \c blockSize number of samples processed at a time
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* \li \c numBlocks number of frames
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*
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* \par CMSIS DSP Software Library Functions Used:
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* \par
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* - arm_fir_init_f32()
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* - arm_fir_f32()
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*
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* <b> Refer </b>
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* \link arm_fir_example_f32.c \endlink
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*
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*/
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/** \example arm_fir_example_f32.c
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*/
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/* ----------------------------------------------------------------------
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** Include Files
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** ------------------------------------------------------------------- */
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#include "arm_math.h"
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#include "math_helper.h"
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/* ----------------------------------------------------------------------
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** Macro Defines
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** ------------------------------------------------------------------- */
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#define TEST_LENGTH_SAMPLES 320
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#define SNR_THRESHOLD_F32 140.0f
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#define BLOCK_SIZE 32
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#define NUM_TAPS 29
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/* -------------------------------------------------------------------
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* The input signal and reference output (computed with MATLAB)
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* are defined externally in arm_fir_lpf_data.c.
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* ------------------------------------------------------------------- */
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extern float32_t testInput_f32_1kHz_15kHz[TEST_LENGTH_SAMPLES];
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extern float32_t refOutput[TEST_LENGTH_SAMPLES];
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/* -------------------------------------------------------------------
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* Declare Test output buffer
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* ------------------------------------------------------------------- */
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static float32_t testOutput[TEST_LENGTH_SAMPLES];
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/* -------------------------------------------------------------------
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* Declare State buffer of size (numTaps + blockSize - 1)
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* ------------------------------------------------------------------- */
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static float32_t firStateF32[BLOCK_SIZE + NUM_TAPS - 1];
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/* ----------------------------------------------------------------------
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** FIR Coefficients buffer generated using fir1() MATLAB function.
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** fir1(28, 6/24)
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** ------------------------------------------------------------------- */
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const float32_t firCoeffs32[NUM_TAPS] = {
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-0.0018225230f, -0.0015879294f, +0.0000000000f, +0.0036977508f, +0.0080754303f, +0.0085302217f, -0.0000000000f, -0.0173976984f,
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-0.0341458607f, -0.0333591565f, +0.0000000000f, +0.0676308395f, +0.1522061835f, +0.2229246956f, +0.2504960933f, +0.2229246956f,
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+0.1522061835f, +0.0676308395f, +0.0000000000f, -0.0333591565f, -0.0341458607f, -0.0173976984f, -0.0000000000f, +0.0085302217f,
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+0.0080754303f, +0.0036977508f, +0.0000000000f, -0.0015879294f, -0.0018225230f
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};
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/* ------------------------------------------------------------------
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* Global variables for FIR LPF Example
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* ------------------------------------------------------------------- */
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uint32_t blockSize = BLOCK_SIZE;
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uint32_t numBlocks = TEST_LENGTH_SAMPLES/BLOCK_SIZE;
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float32_t snr;
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/* ----------------------------------------------------------------------
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* FIR LPF Example
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* ------------------------------------------------------------------- */
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int32_t main(void)
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{
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uint32_t i;
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arm_fir_instance_f32 S;
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arm_status status;
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float32_t *inputF32, *outputF32;
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/* Initialize input and output buffer pointers */
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inputF32 = &testInput_f32_1kHz_15kHz[0];
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outputF32 = &testOutput[0];
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/* Call FIR init function to initialize the instance structure. */
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arm_fir_init_f32(&S, NUM_TAPS, (float32_t *)&firCoeffs32[0], &firStateF32[0], blockSize);
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/* ----------------------------------------------------------------------
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** Call the FIR process function for every blockSize samples
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** ------------------------------------------------------------------- */
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for(i=0; i < numBlocks; i++)
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{
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arm_fir_f32(&S, inputF32 + (i * blockSize), outputF32 + (i * blockSize), blockSize);
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}
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/* ----------------------------------------------------------------------
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** Compare the generated output against the reference output computed
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** in MATLAB.
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** ------------------------------------------------------------------- */
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snr = arm_snr_f32(&refOutput[0], &testOutput[0], TEST_LENGTH_SAMPLES);
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if (snr < SNR_THRESHOLD_F32)
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{
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status = ARM_MATH_TEST_FAILURE;
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}
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else
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{
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status = ARM_MATH_SUCCESS;
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}
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/* ----------------------------------------------------------------------
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** Loop here if the signal does not match the reference output.
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** ------------------------------------------------------------------- */
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if ( status != ARM_MATH_SUCCESS)
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{
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while (1);
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}
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while (1); /* main function does not return */
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}
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/** \endlink */
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