96 lines
3.5 KiB
C
96 lines
3.5 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_biquad_cascade_df1_init_q31.c
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* Description: Q31 Biquad cascade DirectFormI(DF1) filter initialization function
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "arm_math.h"
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/**
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@ingroup groupFilters
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*/
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/**
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@addtogroup BiquadCascadeDF1
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@{
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*/
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/**
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@brief Initialization function for the Q31 Biquad cascade filter.
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@param[in,out] S points to an instance of the Q31 Biquad cascade structure.
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@param[in] numStages number of 2nd order stages in the filter.
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@param[in] pCoeffs points to the filter coefficients.
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@param[in] pState points to the state buffer.
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@param[in] postShift Shift to be applied after the accumulator. Varies according to the coefficients format
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@return none
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@par Coefficient and State Ordering
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The coefficients are stored in the array <code>pCoeffs</code> in the following order:
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<pre>
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{b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
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</pre>
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@par
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where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,
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<code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,
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and so on. The <code>pCoeffs</code> array contains a total of <code>5*numStages</code> values.
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@par
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The <code>pState</code> points to state variables array.
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Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.
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The state variables are arranged in the <code>pState</code> array as:
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<pre>
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{x[n-1], x[n-2], y[n-1], y[n-2]}
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</pre>
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The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.
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The state array has a total length of <code>4*numStages</code> values.
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The state variables are updated after each block of data is processed; the coefficients are untouched.
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*/
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void arm_biquad_cascade_df1_init_q31(
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arm_biquad_casd_df1_inst_q31 * S,
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uint8_t numStages,
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const q31_t * pCoeffs,
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q31_t * pState,
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int8_t postShift)
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{
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/* Assign filter stages */
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S->numStages = numStages;
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/* Assign postShift to be applied to the output */
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S->postShift = postShift;
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/* Assign coefficient pointer */
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S->pCoeffs = pCoeffs;
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/* Clear state buffer and size is always 4 * numStages */
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memset(pState, 0, (4U * (uint32_t) numStages) * sizeof(q31_t));
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/* Assign state pointer */
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S->pState = pState;
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}
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/**
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@} end of BiquadCascadeDF1 group
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*/
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