/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_biquad_cascade_df1_init_q15.c
* Description: Q15 Biquad cascade DirectFormI(DF1) 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 BiquadCascadeDF1
* @{
*/
/**
* @details
*
* @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
*
* Coefficient and State Ordering:
*
* \par
* The coefficients are stored in the array pCoeffs
in the following order:
*
* {b10, 0, b11, b12, a11, a12, b20, 0, b21, b22, a21, a22, ...} ** where
b1x
and a1x
are the coefficients for the first stage,
* b2x
and a2x
are the coefficients for the second stage,
* and so on. The pCoeffs
array contains a total of 6*numStages
values.
* The zero coefficient between b1
and b2
facilities use of 16-bit SIMD instructions on the Cortex-M4.
*
* \par
* The state variables are stored in the array pState
.
* Each Biquad stage has 4 state variables x[n-1], x[n-2], y[n-1],
and y[n-2]
.
* The state variables are arranged in the pState
array as:
* * {x[n-1], x[n-2], y[n-1], y[n-2]} ** 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
4*numStages
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,
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
*/