1 /* ----------------------------------------------------------------------
2 * Project: CMSIS DSP Library
3 * Title: arm_fir_init_q31.c
4 * Description: Q31 FIR filter initialization function.
5 *
6 * $Date: 23 April 2021
7 * $Revision: V1.9.0
8 *
9 * Target Processor: Cortex-M and Cortex-A cores
10 * -------------------------------------------------------------------- */
11 /*
12 * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
13 *
14 * SPDX-License-Identifier: Apache-2.0
15 *
16 * Licensed under the Apache License, Version 2.0 (the License); you may
17 * not use this file except in compliance with the License.
18 * You may obtain a copy of the License at
19 *
20 * www.apache.org/licenses/LICENSE-2.0
21 *
22 * Unless required by applicable law or agreed to in writing, software
23 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
24 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
25 * See the License for the specific language governing permissions and
26 * limitations under the License.
27 */
28
29 #include "dsp/filtering_functions.h"
30
31 /**
32 @ingroup groupFilters
33 */
34
35 /**
36 @addtogroup FIR
37 @{
38 */
39
40 /**
41 @brief Initialization function for the Q31 FIR filter.
42 @param[in,out] S points to an instance of the Q31 FIR filter structure
43 @param[in] numTaps number of filter coefficients in the filter
44 @param[in] pCoeffs points to the filter coefficients buffer
45 @param[in] pState points to the state buffer
46 @param[in] blockSize number of samples processed
47
48 @par Details
49 <code>pCoeffs</code> points to the array of filter coefficients stored in time reversed order:
50 <pre>
51 {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
52 </pre>
53 <code>pState</code> points to the array of state variables.
54 <code>pState</code> is of length <code>numTaps+blockSize-1</code> samples (except for Helium - see below), where <code>blockSize</code> is the number of input samples processed by each call to <code>arm_fir_q31()</code>.
55
56 @par Initialization of Helium version
57 For Helium version the array of coefficients must be a multiple of 4 (4a) even if less
58 then 4a coefficients are defined in the FIR. The additional coefficients
59 (4a - numTaps) must be set to 0.
60 numTaps is still set to its right value in the init function. It means that
61 the implementation may require to read more coefficients due to the vectorization and
62 to avoid having to manage too many different cases in the code.
63
64 @par Helium state buffer
65 The state buffer must contain some additional temporary data
66 used during the computation but which is not the state of the FIR.
67 The first 2*4*ceil(blockSize/4) samples are temporary data.
68 The remaining samples are the state of the FIR filter.
69 So the state buffer has size <code> numTaps + 8*ceil(blockSize/4) + blockSize - 1 </code>
70
71 */
72
arm_fir_init_q31(arm_fir_instance_q31 * S,uint16_t numTaps,const q31_t * pCoeffs,q31_t * pState,uint32_t blockSize)73 void arm_fir_init_q31(
74 arm_fir_instance_q31 * S,
75 uint16_t numTaps,
76 const q31_t * pCoeffs,
77 q31_t * pState,
78 uint32_t blockSize)
79 {
80 /* Assign filter taps */
81 S->numTaps = numTaps;
82
83 /* Assign coefficient pointer */
84 S->pCoeffs = pCoeffs;
85
86 /* Clear state buffer. The size is always (blockSize + numTaps - 1) */
87 #if defined(ARM_MATH_MVEI) && !defined(ARM_MATH_AUTOVECTORIZE)
88 memset(pState, 0, (numTaps + (blockSize - 1U) + 2*ARM_ROUND_UP(blockSize, 4)) * sizeof(q31_t));
89 #else
90 memset(pState, 0, (numTaps + (blockSize - 1U)) * sizeof(q31_t));
91 #endif
92
93 /* Assign state pointer */
94 S->pState = pState;
95 }
96
97 /**
98 @} end of FIR group
99 */
100
