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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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
*
* http://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.
*/
///////////////////////////////////////////////////////////////
/*
* This module implements a sensor stillness detector with a
* look-ahead feature that allows the sensor's mean to be
* computed for an extended stillness period (one-pass, online
* method) sample by sample without a memory buffer. Stillness
* is computed using non-overlapping windows of signal variance
* and thresholding logic. The look-ahead feature ensures that
* the mean computation is not corrupted by the onset of sensor
* activity.
*
* NOTE - Time units are agnostic (i.e., determined by the
* user's application and usage). However, typical time units
* are nanoseconds.
*/
///////////////////////////////////////////////////////////////
#ifndef LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_GYROSCOPE_GYRO_STILLNESS_DETECT_H_
#define LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_GYROSCOPE_GYRO_STILLNESS_DETECT_H_
#include <math.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#ifdef __cplusplus
extern "C" {
#endif
struct GyroStillDet {
// Variance threshold for the stillness confidence score.
float var_threshold; // [sensor units]^2
// Delta about the variance threshold for calculation of the
// stillness confidence score [0,1].
float confidence_delta; // [sensor units]^2
// Flag to indicate when enough samples have been collected for
// a complete stillness calculation.
bool stillness_window_ready;
// Flag to signal the beginning of a new stillness detection window. This
// is used to keep track of the window start time.
bool start_new_window;
// Starting time stamp for the the current window.
uint64_t window_start_time;
// Accumulator variables for tracking the sample mean during
// the stillness period.
uint32_t num_acc_samples;
float mean_x, mean_y, mean_z;
// Accumulator variables for computing the window sample mean and
// variance for the current window (used for stillness detection).
uint32_t num_acc_win_samples;
float win_mean_x, win_mean_y, win_mean_z;
float assumed_mean_x, assumed_mean_y, assumed_mean_z;
float acc_var_x, acc_var_y, acc_var_z;
// Stillness period mean (used for look-ahead).
float prev_mean_x, prev_mean_y, prev_mean_z;
// Latest computed variance.
float win_var_x, win_var_y, win_var_z;
// Stillness confidence score for current and previous sample
// windows [0,1] (used for look-ahead).
float stillness_confidence;
float prev_stillness_confidence;
// Timestamp of last sample recorded.
uint64_t last_sample_time;
};
/////// FUNCTION PROTOTYPES //////////////////////////////////////////
// Initialize the gyro_still_det_t structure.
void gyroStillDetInit(struct GyroStillDet* gyro_still_det,
float var_threshold, float confidence_delta);
// Update the stillness detector with a new sample.
void gyroStillDetUpdate(struct GyroStillDet* gyro_still_det,
uint64_t stillness_win_endtime, uint64_t sample_time,
float x, float y, float z);
// Calculates and returns the stillness confidence score [0,1].
float gyroStillDetCompute(struct GyroStillDet* gyro_still_det);
// Resets the stillness detector and initiates a new detection window.
// 'reset_stats' determines whether the stillness statistics are reset.
void gyroStillDetReset(struct GyroStillDet* gyro_still_det, bool reset_stats);
#ifdef __cplusplus
}
#endif
#endif // LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_GYROSCOPE_GYRO_STILLNESS_DETECT_H_
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