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/* Copyright 2020 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "gyro_still_det.h"
#include "vec3.h"
/* Enforces the limits of an input value [0,1]. */
static fp_t gyro_still_det_limit(fp_t value);
void gyro_still_det_update(struct gyro_still_det *gyro_still_det,
uint32_t stillness_win_endtime, uint32_t sample_time,
fp_t x, fp_t y, fp_t z)
{
fp_t delta = INT_TO_FP(0);
/*
* Using the method of the assumed mean to preserve some numerical
* stability while avoiding per-sample divisions that the more
* numerically stable Welford method would afford.
*
* Reference for the numerical method used below to compute the
* online mean and variance statistics:
* 1). en.wikipedia.org/wiki/assumed_mean
*/
/* Increment the number of samples. */
gyro_still_det->num_acc_samples++;
/* Online computation of mean for the running stillness period. */
gyro_still_det->mean[X] += x;
gyro_still_det->mean[Y] += y;
gyro_still_det->mean[Z] += z;
/* Is this the first sample of a new window? */
if (gyro_still_det->start_new_window) {
/* Record the window start time. */
gyro_still_det->window_start_time = sample_time;
gyro_still_det->start_new_window = false;
/* Update assumed mean values. */
gyro_still_det->assumed_mean[X] = x;
gyro_still_det->assumed_mean[Y] = y;
gyro_still_det->assumed_mean[Z] = z;
/* Reset current window mean and variance. */
gyro_still_det->num_acc_win_samples = 0;
gyro_still_det->win_mean[X] = INT_TO_FP(0);
gyro_still_det->win_mean[Y] = INT_TO_FP(0);
gyro_still_det->win_mean[Z] = INT_TO_FP(0);
gyro_still_det->acc_var[X] = INT_TO_FP(0);
gyro_still_det->acc_var[Y] = INT_TO_FP(0);
gyro_still_det->acc_var[Z] = INT_TO_FP(0);
} else {
/*
* Check to see if we have enough samples to compute a stillness
* confidence score.
*/
gyro_still_det->stillness_window_ready =
(sample_time >= stillness_win_endtime) &&
(gyro_still_det->num_acc_samples > 1);
}
/* Record the most recent sample time stamp. */
gyro_still_det->last_sample_time = sample_time;
/* Online window mean and variance ("one-pass" accumulation). */
gyro_still_det->num_acc_win_samples++;
delta = (x - gyro_still_det->assumed_mean[X]);
gyro_still_det->win_mean[X] += delta;
gyro_still_det->acc_var[X] += fp_sq(delta);
delta = (y - gyro_still_det->assumed_mean[Y]);
gyro_still_det->win_mean[Y] += delta;
gyro_still_det->acc_var[Y] += fp_sq(delta);
delta = (z - gyro_still_det->assumed_mean[Z]);
gyro_still_det->win_mean[Z] += delta;
gyro_still_det->acc_var[Z] += fp_sq(delta);
}
fp_t gyro_still_det_compute(struct gyro_still_det *gyro_still_det)
{
fp_t tmp_denom = INT_TO_FP(1);
fp_t tmp_denom_mean = INT_TO_FP(1);
fp_t tmp;
fp_t upper_var_thresh, lower_var_thresh;
/* Don't divide by zero (not likely, but a precaution). */
if (gyro_still_det->num_acc_win_samples > 1) {
tmp_denom = fp_div(
tmp_denom,
INT_TO_FP(gyro_still_det->num_acc_win_samples - 1));
tmp_denom_mean =
fp_div(tmp_denom_mean,
INT_TO_FP(gyro_still_det->num_acc_win_samples));
} else {
/* Return zero stillness confidence. */
gyro_still_det->stillness_confidence = 0;
return gyro_still_det->stillness_confidence;
}
/* Update the final calculation of window mean and variance. */
tmp = gyro_still_det->win_mean[X];
gyro_still_det->win_mean[X] =
fp_mul(gyro_still_det->win_mean[X], tmp_denom_mean);
gyro_still_det->win_var[X] =
fp_mul((gyro_still_det->acc_var[X] -
fp_mul(gyro_still_det->win_mean[X], tmp)),
tmp_denom);
tmp = gyro_still_det->win_mean[Y];
gyro_still_det->win_mean[Y] =
fp_mul(gyro_still_det->win_mean[Y], tmp_denom_mean);
gyro_still_det->win_var[Y] =
fp_mul((gyro_still_det->acc_var[Y] -
fp_mul(gyro_still_det->win_mean[Y], tmp)),
tmp_denom);
tmp = gyro_still_det->win_mean[Z];
gyro_still_det->win_mean[Z] =
fp_mul(gyro_still_det->win_mean[Z], tmp_denom_mean);
gyro_still_det->win_var[Z] =
fp_mul((gyro_still_det->acc_var[Z] -
fp_mul(gyro_still_det->win_mean[Z], tmp)),
tmp_denom);
/* Adds the assumed mean value back to the total mean calculation. */
gyro_still_det->win_mean[X] += gyro_still_det->assumed_mean[X];
gyro_still_det->win_mean[Y] += gyro_still_det->assumed_mean[Y];
gyro_still_det->win_mean[Z] += gyro_still_det->assumed_mean[Z];
/* Define the variance thresholds. */
upper_var_thresh = gyro_still_det->var_threshold +
gyro_still_det->confidence_delta;
lower_var_thresh = gyro_still_det->var_threshold -
gyro_still_det->confidence_delta;
/* Compute the stillness confidence score. */
if ((gyro_still_det->win_var[X] > upper_var_thresh) ||
(gyro_still_det->win_var[Y] > upper_var_thresh) ||
(gyro_still_det->win_var[Z] > upper_var_thresh)) {
/*
* Sensor variance exceeds the upper threshold (i.e., motion
* detected). Set stillness confidence equal to 0.
*/
gyro_still_det->stillness_confidence = 0;
} else if ((gyro_still_det->win_var[X] <= lower_var_thresh) &&
(gyro_still_det->win_var[Y] <= lower_var_thresh) &&
(gyro_still_det->win_var[Z] <= lower_var_thresh)) {
/*
* Sensor variance is below the lower threshold (i.e.
* stillness detected).
* Set stillness confidence equal to 1.
*/
gyro_still_det->stillness_confidence = INT_TO_FP(1);
} else {
/*
* Motion detection thresholds not exceeded. Compute the
* stillness confidence score.
*/
fp_t var_thresh = gyro_still_det->var_threshold;
fpv3_t limit;
/*
* Compute the stillness confidence score.
* Each axis score is limited [0,1].
*/
tmp_denom = fp_div(INT_TO_FP(1),
(upper_var_thresh - lower_var_thresh));
limit[X] = gyro_still_det_limit(
FLOAT_TO_FP(0.5f) -
fp_mul(gyro_still_det->win_var[X] - var_thresh,
tmp_denom));
limit[Y] = gyro_still_det_limit(
FLOAT_TO_FP(0.5f) -
fp_mul(gyro_still_det->win_var[Y] - var_thresh,
tmp_denom));
limit[Z] = gyro_still_det_limit(
FLOAT_TO_FP(0.5f) -
fp_mul(gyro_still_det->win_var[Z] - var_thresh,
tmp_denom));
gyro_still_det->stillness_confidence =
fp_mul(limit[X], fp_mul(limit[Y], limit[Z]));
}
/* Return the stillness confidence. */
return gyro_still_det->stillness_confidence;
}
void gyro_still_det_reset(struct gyro_still_det *gyro_still_det,
bool reset_stats)
{
fp_t tmp_denom = INT_TO_FP(1);
/* Reset the stillness data ready flag. */
gyro_still_det->stillness_window_ready = false;
/* Signal to start capture of next stillness data window. */
gyro_still_det->start_new_window = true;
/* Track the stillness confidence (current->previous). */
gyro_still_det->prev_stillness_confidence =
gyro_still_det->stillness_confidence;
/* Track changes in the mean estimate. */
if (gyro_still_det->num_acc_samples > INT_TO_FP(1))
tmp_denom =
fp_div(INT_TO_FP(1), gyro_still_det->num_acc_samples);
gyro_still_det->prev_mean[X] =
fp_mul(gyro_still_det->mean[X], tmp_denom);
gyro_still_det->prev_mean[Y] =
fp_mul(gyro_still_det->mean[Y], tmp_denom);
gyro_still_det->prev_mean[Z] =
fp_mul(gyro_still_det->mean[Z], tmp_denom);
/* Reset the current statistics to zero. */
if (reset_stats) {
gyro_still_det->num_acc_samples = 0;
gyro_still_det->mean[X] = INT_TO_FP(0);
gyro_still_det->mean[Y] = INT_TO_FP(0);
gyro_still_det->mean[Z] = INT_TO_FP(0);
gyro_still_det->acc_var[X] = INT_TO_FP(0);
gyro_still_det->acc_var[Y] = INT_TO_FP(0);
gyro_still_det->acc_var[Z] = INT_TO_FP(0);
}
}
fp_t gyro_still_det_limit(fp_t value)
{
if (value < INT_TO_FP(0))
value = INT_TO_FP(0);
else if (value > INT_TO_FP(1))
value = INT_TO_FP(1);
return value;
}
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