pigweed / third_party / github / STMicroelectronics / cmsis_core / be0e91fb4ba19a2ee427ba8b6b75b43eb02b2810 / . / DSP / Source / FilteringFunctions / arm_fir_init_q15.c

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

* Project: CMSIS DSP Library | |

* Title: arm_fir_init_q15.c | |

* Description: Q15 FIR 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 FIR | |

@{ | |

*/ | |

/** | |

@brief Initialization function for the Q15 FIR filter. | |

@param[in,out] S points to an instance of the Q15 FIR filter structure. | |

@param[in] numTaps number of filter coefficients in the filter. Must be even and greater than or equal to 4. | |

@param[in] pCoeffs points to the filter coefficients buffer. | |

@param[in] pState points to the state buffer. | |

@param[in] blockSize number of samples processed per call. | |

@return execution status | |

- \ref ARM_MATH_SUCCESS : Operation successful | |

- \ref ARM_MATH_ARGUMENT_ERROR : <code>numTaps</code> is not greater than or equal to 4 and even | |

@par Details | |

<code>pCoeffs</code> points to the array of filter coefficients stored in time reversed order: | |

<pre> | |

{b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]} | |

</pre> | |

Note that <code>numTaps</code> must be even and greater than or equal to 4. | |

To implement an odd length filter simply increase <code>numTaps</code> by 1 and set the last coefficient to zero. | |

For example, to implement a filter with <code>numTaps=3</code> and coefficients | |

<pre> | |

{0.3, -0.8, 0.3} | |

</pre> | |

set <code>numTaps=4</code> and use the coefficients: | |

<pre> | |

{0.3, -0.8, 0.3, 0}. | |

</pre> | |

Similarly, to implement a two point filter | |

<pre> | |

{0.3, -0.3} | |

</pre> | |

set <code>numTaps=4</code> and use the coefficients: | |

<pre> | |

{0.3, -0.3, 0, 0}. | |

</pre> | |

<code>pState</code> points to the array of state variables. | |

<code>pState</code> is of length <code>numTaps+blockSize</code>, when running on Cortex-M4 and Cortex-M3 and is of length <code>numTaps+blockSize-1</code>, when running on Cortex-M0 where <code>blockSize</code> is the number of input samples processed by each call to <code>arm_fir_q15()</code>. | |

*/ | |

arm_status arm_fir_init_q15( | |

arm_fir_instance_q15 * S, | |

uint16_t numTaps, | |

const q15_t * pCoeffs, | |

q15_t * pState, | |

uint32_t blockSize) | |

{ | |

arm_status status; | |

#if defined (ARM_MATH_DSP) | |

/* The Number of filter coefficients in the filter must be even and at least 4 */ | |

if (numTaps & 0x1U) | |

{ | |

status = ARM_MATH_ARGUMENT_ERROR; | |

} | |

else | |

{ | |

/* Assign filter taps */ | |

S->numTaps = numTaps; | |

/* Assign coefficient pointer */ | |

S->pCoeffs = pCoeffs; | |

/* Clear the state buffer. The size is always (blockSize + numTaps ) */ | |

memset(pState, 0, (numTaps + (blockSize)) * sizeof(q15_t)); | |

/* Assign state pointer */ | |

S->pState = pState; | |

status = ARM_MATH_SUCCESS; | |

} | |

return (status); | |

#else | |

/* Assign filter taps */ | |

S->numTaps = numTaps; | |

/* Assign coefficient pointer */ | |

S->pCoeffs = pCoeffs; | |

/* Clear state buffer. The size is always (blockSize + numTaps - 1) */ | |

memset(pState, 0, (numTaps + (blockSize - 1U)) * sizeof(q15_t)); | |

/* Assign state pointer */ | |

S->pState = pState; | |

status = ARM_MATH_SUCCESS; | |

return (status); | |

#endif /* #if defined (ARM_MATH_DSP) */ | |

} | |

/** | |

@} end of FIR group | |

*/ |