pigweed / third_party / github / STMicroelectronics / cmsis_core / refs/heads/cm4 / . / DSP / Source / FilteringFunctions / arm_biquad_cascade_df1_init_q15.c

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

* 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 | |

*/ |