DSP/Source/FilteringFunctions/arm_biquad_cascade_df1_init_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_biquad_cascade_df1_init_q15.c
 * Description:  Q15 Biquad cascade DirectFormI(DF1) filter initialization function
 *
 * $Date:        18. March 2019
 * $Revision:    V1.6.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 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 BiquadCascadeDF1
  @{
 */

/**
  @brief         Initialization function for the Q15 Biquad cascade filter.
  @param[in,out] S           points to an instance of the Q15 Biquad cascade structure.
  @param[in]     numStages   number of 2nd order stages in the filter.
  @param[in]     pCoeffs     points to the filter coefficients.
  @param[in]     pState      points to the state buffer.
  @param[in]     postShift   Shift to be applied to the accumulator result. Varies according to the coefficients format
  @return        none

  @par           Coefficient and State Ordering
                   The coefficients are stored in the array <code>pCoeffs</code> in the following order:
  <pre>
      {b10, 0, b11, b12, a11, a12, b20, 0, b21, b22, a21, a22, ...}
  </pre>
  @par
                   where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,
                   <code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,
                   and so on.  The <code>pCoeffs</code> array contains a total of <code>6*numStages</code> values.
                   The zero coefficient between <code>b1</code> and <code>b2</code> facilities  use of 16-bit SIMD instructions on the Cortex-M4.
  @par
                   The state variables are stored in the array <code>pState</code>.
                   Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.
                   The state variables are arranged in the <code>pState</code> array as:
  <pre>
      {x[n-1], x[n-2], y[n-1], y[n-2]}
  </pre>
                   The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.
                   The state array has a total length of <code>4*numStages</code> values.
                   The state variables are updated after each block of data is processed; the coefficients are untouched.
 */

void arm_biquad_cascade_df1_init_q15(
        arm_biquad_casd_df1_inst_q15 * S,
        uint8_t numStages,
  const q15_t * pCoeffs,
        q15_t * pState,
        int8_t postShift)
{
  /* Assign filter stages */
  S->numStages = numStages;

  /* Assign postShift to be applied to the output */
  S->postShift = postShift;

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

  /* Clear state buffer and size is always 4 * numStages */
  memset(pState, 0, (4U * (uint32_t) numStages) * sizeof(q15_t));

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

/**
  @} end of BiquadCascadeDF1 group
 */