N3_sub/libraries/Filter/HarmonicNotchFilter.h

/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#pragma once

#include <AP_Math/AP_Math.h>
#include <cmath>
#include <AP_Param/AP_Param.h>
#include "NotchFilter.h"

/*
  a filter that manages a set of notch filters targetted at a fundamental center frequency
  and multiples of that fundamental frequency
 */
template <class T>
class HarmonicNotchFilter {
public:
    ~HarmonicNotchFilter();
    // allocate a bank of notch filters for this harmonic notch filter
    void allocate_filters(uint8_t harmonics);
    // initialize the underlying filters using the provided filter parameters
    void init(float sample_freq_hz, float center_freq_hz, float bandwidth_hz, float attenuation_dB);
    // update the underlying filters' center frequencies using center_freq_hz as the fundamental
    void update(float center_freq_hz);
    // apply a sample to each of the underlying filters in turn
    T apply(const T &sample);
    // reset each of the underlying filters
    void reset();

private:
    // underlying bank of notch filters
    NotchFilter<T>*  _filters;
    // sample frequency for each filter
    float _sample_freq_hz;
    // attenuation for each filter
    float _A;
    // quality factor of each filter
    float _Q;
    // a bitmask of the harmonics to use
    uint8_t _harmonics;
    // number of allocated filters
    uint8_t _num_filters;
    // number of enabled filters
    uint8_t _num_enabled_filters;
    bool _initialised;
};

/*
  harmonic notch filter configuration parameters
 */
class HarmonicNotchFilterParams : public NotchFilterParams {
public:
    HarmonicNotchFilterParams(void);
    // set the fundamental center frequency of the harmonic notch
    void set_center_freq_hz(float center_freq) { _center_freq_hz.set(center_freq); }
    // harmonics enabled on the harmonic notch
    uint8_t harmonics(void) const { return _harmonics; }
    // reference value of the harmonic notch
    float reference(void) const { return _reference; }
    static const struct AP_Param::GroupInfo var_info[];

private:
    // notch harmonics
    AP_Int8 _harmonics;
    // notch reference value
    AP_Float _reference;
};

typedef HarmonicNotchFilter<Vector3f> HarmonicNotchFilterVector3f;