/*
*      $NetBSD: sensirion_voc_algorithm.h,v 1.2 2022/09/25 12:41:46 andvar Exp $
*/

/*
* Copyright (c) 2021, Sensirion AG
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
*   list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
*   this list of conditions and the following disclaimer in the documentation
*   and/or other materials provided with the distribution.
*
* * Neither the name of Sensirion AG nor the names of its
*   contributors may be used to endorse or promote products derived from
*   this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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*/

#ifndef VOCALGORITHM_H_
#define VOCALGORITHM_H_

#include "sensirion_arch_config.h"

/* The fixed point arithmetic parts of this code were originally created by
* https://github.com/PetteriAimonen/libfixmath
*/

typedef int32_t fix16_t;

#define F16(x) \
   ((fix16_t)(((x) >= 0) ? ((x)*65536.0 + 0.5) : ((x)*65536.0 - 0.5)))

// Should be set by the building toolchain
#ifndef LIBRARY_VERSION_NAME
#define LIBRARY_VERSION_NAME "custom build"
#endif

#define VocAlgorithm_SAMPLING_INTERVAL (1.)
#define VocAlgorithm_INITIAL_BLACKOUT (45.)
#define VocAlgorithm_VOC_INDEX_GAIN (230.)
#define VocAlgorithm_SRAW_STD_INITIAL (50.)
#define VocAlgorithm_SRAW_STD_BONUS (220.)
#define VocAlgorithm_TAU_MEAN_VARIANCE_HOURS (12.)
#define VocAlgorithm_TAU_INITIAL_MEAN (20.)
#define VocAlgorithm_INIT_DURATION_MEAN ((3600. * 0.75))
#define VocAlgorithm_INIT_TRANSITION_MEAN (0.01)
#define VocAlgorithm_TAU_INITIAL_VARIANCE (2500.)
#define VocAlgorithm_INIT_DURATION_VARIANCE ((3600. * 1.45))
#define VocAlgorithm_INIT_TRANSITION_VARIANCE (0.01)
#define VocAlgorithm_GATING_THRESHOLD (340.)
#define VocAlgorithm_GATING_THRESHOLD_INITIAL (510.)
#define VocAlgorithm_GATING_THRESHOLD_TRANSITION (0.09)
#define VocAlgorithm_GATING_MAX_DURATION_MINUTES ((60. * 3.))
#define VocAlgorithm_GATING_MAX_RATIO (0.3)
#define VocAlgorithm_SIGMOID_L (500.)
#define VocAlgorithm_SIGMOID_K (-0.0065)
#define VocAlgorithm_SIGMOID_X0 (213.)
#define VocAlgorithm_VOC_INDEX_OFFSET_DEFAULT (100.)
#define VocAlgorithm_LP_TAU_FAST (20.0)
#define VocAlgorithm_LP_TAU_SLOW (500.0)
#define VocAlgorithm_LP_ALPHA (-0.2)
#define VocAlgorithm_PERSISTENCE_UPTIME_GAMMA ((3. * 3600.))
#define VocAlgorithm_MEAN_VARIANCE_ESTIMATOR__GAMMA_SCALING (64.)
#define VocAlgorithm_MEAN_VARIANCE_ESTIMATOR__FIX16_MAX (32767.)

/**
* Struct to hold all the states of the VOC algorithm.
*/
typedef struct {
   fix16_t mVoc_Index_Offset;
   fix16_t mTau_Mean_Variance_Hours;
   fix16_t mGating_Max_Duration_Minutes;
   fix16_t mSraw_Std_Initial;
   fix16_t mUptime;
   fix16_t mSraw;
   fix16_t mVoc_Index;
   fix16_t m_Mean_Variance_Estimator__Gating_Max_Duration_Minutes;
   bool m_Mean_Variance_Estimator___Initialized;
   fix16_t m_Mean_Variance_Estimator___Mean;
   fix16_t m_Mean_Variance_Estimator___Sraw_Offset;
   fix16_t m_Mean_Variance_Estimator___Std;
   fix16_t m_Mean_Variance_Estimator___Gamma;
   fix16_t m_Mean_Variance_Estimator___Gamma_Initial_Mean;
   fix16_t m_Mean_Variance_Estimator___Gamma_Initial_Variance;
   fix16_t m_Mean_Variance_Estimator__Gamma_Mean;
   fix16_t m_Mean_Variance_Estimator__Gamma_Variance;
   fix16_t m_Mean_Variance_Estimator___Uptime_Gamma;
   fix16_t m_Mean_Variance_Estimator___Uptime_Gating;
   fix16_t m_Mean_Variance_Estimator___Gating_Duration_Minutes;
   fix16_t m_Mean_Variance_Estimator___Sigmoid__L;
   fix16_t m_Mean_Variance_Estimator___Sigmoid__K;
   fix16_t m_Mean_Variance_Estimator___Sigmoid__X0;
   fix16_t m_Mox_Model__Sraw_Std;
   fix16_t m_Mox_Model__Sraw_Mean;
   fix16_t m_Sigmoid_Scaled__Offset;
   fix16_t m_Adaptive_Lowpass__A1;
   fix16_t m_Adaptive_Lowpass__A2;
   bool m_Adaptive_Lowpass___Initialized;
   fix16_t m_Adaptive_Lowpass___X1;
   fix16_t m_Adaptive_Lowpass___X2;
   fix16_t m_Adaptive_Lowpass___X3;
} VocAlgorithmParams;

/**
* Initialize the VOC algorithm parameters. Call this once at the beginning or
* whenever the sensor stopped measurements.
* @param params    Pointer to the VocAlgorithmParams struct
*/
void VocAlgorithm_init(VocAlgorithmParams* params);

/**
* Get current algorithm states. Retrieved values can be used in
* VocAlgorithm_set_states() to resume operation after a short interruption,
* skipping initial learning phase. This feature can only be used after at least
* 3 hours of continuous operation.
* @param params    Pointer to the VocAlgorithmParams struct
* @param state0    State0 to be stored
* @param state1    State1 to be stored
*/
void VocAlgorithm_get_states(VocAlgorithmParams* params, int32_t* state0,
                            int32_t* state1);

/**
* Set previously retrieved algorithm states to resume operation after a short
* interruption, skipping initial learning phase. This feature should not be
* used after interruptions of more than 10 minutes. Call this once after
* VocAlgorithm_init() and the optional VocAlgorithm_set_tuning_parameters(), if
* desired. Otherwise, the algorithm will start with initial learning phase.
* @param params    Pointer to the VocAlgorithmParams struct
* @param state0    State0 to be restored
* @param state1    State1 to be restored
*/
void VocAlgorithm_set_states(VocAlgorithmParams* params, int32_t state0,
                            int32_t state1);

/**
* Set parameters to customize the VOC algorithm. Call this once after
* VocAlgorithm_init(), if desired. Otherwise, the default values will be used.
*
* @param params                      Pointer to the VocAlgorithmParams struct
* @param voc_index_offset            VOC index representing typical (average)
*                                    conditions. Range 1..250, default 100
* @param learning_time_hours         Time constant of long-term estimator.
*                                    Past events will be forgotten after about
*                                    twice the learning time.
*                                    Range 1..72 [hours], default 12 [hours]
* @param gating_max_duration_minutes Maximum duration of gating (freeze of
*                                    estimator during high VOC index signal).
*                                    0 (no gating) or range 1..720 [minutes],
*                                    default 180 [minutes]
* @param std_initial                 Initial estimate for standard deviation.
*                                    Lower value boosts events during initial
*                                    learning period, but may result in larger
*                                    device-to-device variations.
*                                    Range 10..500, default 50
*/
void VocAlgorithm_set_tuning_parameters(VocAlgorithmParams* params,
                                       int32_t voc_index_offset,
                                       int32_t learning_time_hours,
                                       int32_t gating_max_duration_minutes,
                                       int32_t std_initial);

/**
* Calculate the VOC index value from the raw sensor value.
*
* @param params    Pointer to the VocAlgorithmParams struct
* @param sraw      Raw value from the SGP40 sensor
* @param voc_index Calculated VOC index value from the raw sensor value. Zero
*                  during initial blackout period and 1..500 afterwards
*/
void VocAlgorithm_process(VocAlgorithmParams* params, int32_t sraw,
                         int32_t* voc_index);

#endif /* VOCALGORITHM_H_ */

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