1 /*-----------------------------------------------------------------------------
2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
4 * $Date: 17. January 2013
7 * Project: CMSIS DSP Library
8 * Title: arm_biquad_cascade_df1_init_q15.c
10 * Description: Q15 Biquad cascade DirectFormI(DF1) filter initialization function.
12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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15 * modification, are permitted provided that the following conditions
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25 * software without specific prior written permission.
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39 * ---------------------------------------------------------------------------*/
44 * @ingroup groupFilters
48 * @addtogroup BiquadCascadeDF1
55 * @param[in,out] *S points to an instance of the Q15 Biquad cascade structure.
56 * @param[in] numStages number of 2nd order stages in the filter.
57 * @param[in] *pCoeffs points to the filter coefficients.
58 * @param[in] *pState points to the state buffer.
59 * @param[in] postShift Shift to be applied to the accumulator result. Varies according to the coefficients format
62 * <b>Coefficient and State Ordering:</b>
65 * The coefficients are stored in the array <code>pCoeffs</code> in the following order:
67 * {b10, 0, b11, b12, a11, a12, b20, 0, b21, b22, a21, a22, ...}
69 * where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,
70 * <code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,
71 * and so on. The <code>pCoeffs</code> array contains a total of <code>6*numStages</code> values.
72 * The zero coefficient between <code>b1</code> and <code>b2</code> facilities use of 16-bit SIMD instructions on the Cortex-M4.
75 * The state variables are stored in the array <code>pState</code>.
76 * Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.
77 * The state variables are arranged in the <code>pState</code> array as:
79 * {x[n-1], x[n-2], y[n-1], y[n-2]}
81 * The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.
82 * The state array has a total length of <code>4*numStages</code> values.
83 * The state variables are updated after each block of data is processed; the coefficients are untouched.
86 void arm_biquad_cascade_df1_init_q15(
87 arm_biquad_casd_df1_inst_q15
* S
,
93 /* Assign filter stages */
94 S
->numStages
= numStages
;
96 /* Assign postShift to be applied to the output */
97 S
->postShift
= postShift
;
99 /* Assign coefficient pointer */
100 S
->pCoeffs
= pCoeffs
;
102 /* Clear state buffer and size is always 4 * numStages */
103 memset(pState
, 0, (4u * (uint32_t) numStages
) * sizeof(q15_t
));
105 /* Assign state pointer */
110 * @} end of BiquadCascadeDF1 group