| /* ---------------------------------------------------------------------- |
| * 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 |
| */ |