/* ---------------------------------------------------------------------- * 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 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * -------------------------------------------------------------------- */ /** * @addtogroup 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: * 
 *     h = fir1(28, 6/24);
 *
* 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. * 
 *     fliplr(h)
 *
* 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() * * Refer * \link arm_fir_example_f32.c \endlink * * \example arm_fir_example_f32.c * * @} */ /* ---------------------------------------------------------------------- ** Include Files ** ------------------------------------------------------------------- */ #include "arm_math.h" #include "math_helper.h" #if defined(SEMIHOSTING) #include #endif /* ---------------------------------------------------------------------- ** Macro Defines ** ------------------------------------------------------------------- */ #define TEST_LENGTH_SAMPLES 320 /* This SNR is a bit small. Need to understand why this example is not giving better SNR ... */ #define SNR_THRESHOLD_F32 75.0f #define BLOCK_SIZE 32 #if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) /* Must be a multiple of 16 */ #define NUM_TAPS_ARRAY_SIZE 32 #else #define NUM_TAPS_ARRAY_SIZE 29 #endif #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) * ------------------------------------------------------------------- */ #if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) static float32_t firStateF32[2 * BLOCK_SIZE + NUM_TAPS - 1]; #else static float32_t firStateF32[BLOCK_SIZE + NUM_TAPS - 1]; #endif /* ---------------------------------------------------------------------- ** FIR Coefficients buffer generated using fir1() MATLAB function. ** fir1(28, 6/24) ** ------------------------------------------------------------------- */ #if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) const float32_t firCoeffs32[NUM_TAPS_ARRAY_SIZE] = { -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, 0.0f,0.0f,0.0f }; #else const float32_t firCoeffs32[NUM_TAPS_ARRAY_SIZE] = { -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 }; #endif /* ------------------------------------------------------------------ * 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); status = (snr < SNR_THRESHOLD_F32) ? ARM_MATH_TEST_FAILURE : ARM_MATH_SUCCESS; if (status != ARM_MATH_SUCCESS) { #if defined (SEMIHOSTING) printf("FAILURE\n"); #else while (1); /* main function does not return */ #endif } else { #if defined (SEMIHOSTING) printf("SUCCESS\n"); #else while (1); /* main function does not return */ #endif } } /** \endlink */