DSP/Source/FilteringFunctions/arm_fir_init_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_fir_init_q15.c
 * Description:  Q15 FIR filter initialization function
 *
 * $Date:        27. January 2017
 * $Revision:    V.1.5.1
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup FIR
 * @{
 */

/**
 * @param[in,out]  *S points to an instance of the Q15 FIR filter structure.
 * @param[in] 	   numTaps  Number of filter coefficients in the filter. Must be even and greater than or equal to 4.
 * @param[in]      *pCoeffs points to the filter coefficients buffer.
 * @param[in]      *pState points to the state buffer.
 * @param[in]      blockSize is number of samples processed per call.
 * @return The function returns ARM_MATH_SUCCESS if initialization is successful or ARM_MATH_ARGUMENT_ERROR if
 * <code>numTaps</code> is not greater than or equal to 4 and even.
 *
 * <b>Description:</b>
 * \par
 * <code>pCoeffs</code> points to the array of filter coefficients stored in time reversed order:
 * <pre>
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 * </pre>
 * Note that <code>numTaps</code> must be even and greater than or equal to 4.
 * To implement an odd length filter simply increase <code>numTaps</code> by 1 and set the last coefficient to zero.
 * For example, to implement a filter with <code>numTaps=3</code> and coefficients
 * <pre>
 *     {0.3, -0.8, 0.3}
 * </pre>
 * set <code>numTaps=4</code> and use the coefficients:
 * <pre>
 *     {0.3, -0.8, 0.3, 0}.
 * </pre>
 * Similarly, to implement a two point filter
 * <pre>
 *     {0.3, -0.3}
 * </pre>
 * set <code>numTaps=4</code> and use the coefficients:
 * <pre>
 *     {0.3, -0.3, 0, 0}.
 * </pre>
 * \par
 * <code>pState</code> points to the array of state variables.
 * <code>pState</code> is of length <code>numTaps+blockSize</code>, when running on Cortex-M4 and Cortex-M3  and is of length <code>numTaps+blockSize-1</code>, when running on Cortex-M0 where <code>blockSize</code> is the number of input samples processed by each call to <code>arm_fir_q15()</code>.
 */

arm_status arm_fir_init_q15(
  arm_fir_instance_q15 * S,
  uint16_t numTaps,
  q15_t * pCoeffs,
  q15_t * pState,
  uint32_t blockSize)
{
  arm_status status;


#if defined (ARM_MATH_DSP)

  /* Run the below code for Cortex-M4 and Cortex-M3 */

  /* The Number of filter coefficients in the filter must be even and at least 4 */
  if (numTaps & 0x1U)
  {
    status = ARM_MATH_ARGUMENT_ERROR;
  }
  else
  {
    /* Assign filter taps */
    S->numTaps = numTaps;

    /* Assign coefficient pointer */
    S->pCoeffs = pCoeffs;

    /* Clear the state buffer.  The size is always (blockSize + numTaps ) */
    memset(pState, 0, (numTaps + (blockSize)) * sizeof(q15_t));

    /* Assign state pointer */
    S->pState = pState;

    status = ARM_MATH_SUCCESS;
  }

  return (status);

#else

  /* Run the below code for Cortex-M0 */

  /* Assign filter taps */
  S->numTaps = numTaps;

  /* Assign coefficient pointer */
  S->pCoeffs = pCoeffs;

  /* Clear the state buffer.  The size is always (blockSize + numTaps - 1) */
  memset(pState, 0, (numTaps + (blockSize - 1U)) * sizeof(q15_t));

  /* Assign state pointer */
  S->pState = pState;

  status = ARM_MATH_SUCCESS;

  return (status);

#endif /*  #if defined (ARM_MATH_DSP) */

}

/**
 * @} end of FIR group
 */