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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:

+*   - 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.

+ * -------------------------------------------------------------------- */

+

+/**

+ * @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 */