1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
|
/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_biquad_cascade_df1_q31.c
* Description: Processing function for the Q31 Biquad cascade filter
*
* $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 Processing function for the Q31 Biquad cascade filter.
@param[in] S points to an instance of the Q31 Biquad cascade structure
@param[in] pSrc points to the block of input data
@param[out] pDst points to the block of output data
@param[in] blockSize number of samples to process
@return none
@par Scaling and Overflow Behavior
The function is implemented using an internal 64-bit accumulator.
The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
Thus, if the accumulator result overflows it wraps around rather than clip.
In order to avoid overflows completely the input signal must be scaled down by 2 bits and lie in the range [-0.25 +0.25).
After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by <code>postShift</code> bits and the result truncated to
1.31 format by discarding the low 32 bits.
@remark
Refer to \ref arm_biquad_cascade_df1_fast_q31() for a faster but less precise implementation of this filter.
*/
void arm_biquad_cascade_df1_q31(
const arm_biquad_casd_df1_inst_q31 * S,
const q31_t * pSrc,
q31_t * pDst,
uint32_t blockSize)
{
const q31_t *pIn = pSrc; /* Source pointer */
q31_t *pOut = pDst; /* Destination pointer */
q31_t *pState = S->pState; /* pState pointer */
const q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
q63_t acc; /* Accumulator */
q31_t b0, b1, b2, a1, a2; /* Filter coefficients */
q31_t Xn1, Xn2, Yn1, Yn2; /* Filter pState variables */
q31_t Xn; /* Temporary input */
uint32_t uShift = ((uint32_t) S->postShift + 1U);
uint32_t lShift = 32U - uShift; /* Shift to be applied to the output */
uint32_t sample, stage = S->numStages; /* Loop counters */
#if defined (ARM_MATH_LOOPUNROLL)
q31_t acc_l, acc_h; /* temporary output variables */
#endif
do
{
/* Reading the coefficients */
b0 = *pCoeffs++;
b1 = *pCoeffs++;
b2 = *pCoeffs++;
a1 = *pCoeffs++;
a2 = *pCoeffs++;
/* Reading the pState values */
Xn1 = pState[0];
Xn2 = pState[1];
Yn1 = pState[2];
Yn2 = pState[3];
#if defined (ARM_MATH_LOOPUNROLL)
/* Apply loop unrolling and compute 4 output values simultaneously. */
/* Variable acc hold output values that are being computed:
*
* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
*/
/* Loop unrolling: Compute 4 outputs at a time */
sample = blockSize >> 2U;
while (sample > 0U)
{
/* Read the first input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2);
/* The result is converted to 1.31 , Yn2 variable is reused */
acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */
acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */
/* Apply shift for lower part of acc and upper part of acc */
Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift;
/* Store output in destination buffer. */
*pOut++ = Yn2;
/* Read the second input */
Xn2 = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
acc = ((q63_t) b0 * Xn2) + ((q63_t) b1 * Xn) + ((q63_t) b2 * Xn1) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1);
/* The result is converted to 1.31, Yn1 variable is reused */
acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */
acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */
/* Apply shift for lower part of acc and upper part of acc */
Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift;
/* Store output in destination buffer. */
*pOut++ = Yn1;
/* Read the third input */
Xn1 = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
acc = ((q63_t) b0 * Xn1) + ((q63_t) b1 * Xn2) + ((q63_t) b2 * Xn) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2);
/* The result is converted to 1.31, Yn2 variable is reused */
acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */
acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */
/* Apply shift for lower part of acc and upper part of acc */
Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift;
/* Store output in destination buffer. */
*pOut++ = Yn2;
/* Read the forth input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1);
/* The result is converted to 1.31, Yn1 variable is reused */
acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */
acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */
/* Apply shift for lower part of acc and upper part of acc */
Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift;
/* Store output in destination buffer. */
*pOut++ = Yn1;
/* Every time after the output is computed state should be updated. */
/* The states should be updated as: */
/* Xn2 = Xn1 */
/* Xn1 = Xn */
/* Yn2 = Yn1 */
/* Yn1 = acc */
Xn2 = Xn1;
Xn1 = Xn;
/* decrement loop counter */
sample--;
}
/* Loop unrolling: Compute remaining outputs */
sample = blockSize & 0x3U;
#else
/* Initialize blkCnt with number of samples */
sample = blockSize;
#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
while (sample > 0U)
{
/* Read the input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2);
/* The result is converted to 1.31 */
acc = acc >> lShift;
/* Store output in destination buffer. */
*pOut++ = (q31_t) acc;
/* Every time after the output is computed state should be updated. */
/* The states should be updated as: */
/* Xn2 = Xn1 */
/* Xn1 = Xn */
/* Yn2 = Yn1 */
/* Yn1 = acc */
Xn2 = Xn1;
Xn1 = Xn;
Yn2 = Yn1;
Yn1 = (q31_t) acc;
/* decrement loop counter */
sample--;
}
/* Store the updated state variables back into the pState array */
*pState++ = Xn1;
*pState++ = Xn2;
*pState++ = Yn1;
*pState++ = Yn2;
/* The first stage goes from the input buffer to the output buffer. */
/* Subsequent numStages occur in-place in the output buffer */
pIn = pDst;
/* Reset output pointer */
pOut = pDst;
/* decrement loop counter */
stage--;
} while (stage > 0U);
}
/**
@} end of BiquadCascadeDF1 group
*/
|
