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/* Copyright 2019 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 "common.h"
#include "stillness_detector.h"
#include "timer.h"
#include <string.h>
static void still_det_reset(struct still_det *still_det)
{
still_det->num_samples = 0;
still_det->acc_x = FLOAT_TO_FP(0.0f);
still_det->acc_y = FLOAT_TO_FP(0.0f);
still_det->acc_z = FLOAT_TO_FP(0.0f);
still_det->acc_xx = FLOAT_TO_FP(0.0f);
still_det->acc_yy = FLOAT_TO_FP(0.0f);
still_det->acc_zz = FLOAT_TO_FP(0.0f);
}
static bool stillness_batch_complete(struct still_det *still_det,
uint32_t sample_time)
{
bool complete = false;
uint32_t batch_window = time_until(still_det->window_start_time,
sample_time);
/* Checking if enough data is accumulated */
if (batch_window >= still_det->min_batch_window &&
still_det->num_samples > still_det->min_batch_size) {
if (batch_window <= still_det->max_batch_window) {
complete = true;
} else {
/* Checking for too long batch window, reset and start
* over
*/
still_det_reset(still_det);
}
} else if (batch_window > still_det->min_batch_window &&
still_det->num_samples < still_det->min_batch_size) {
/* Not enough samples collected, reset and start over */
still_det_reset(still_det);
}
return complete;
}
static inline fp_t compute_variance(fp_t acc_squared, fp_t acc, fp_t inv)
{
/* (acc^2 - (acc * acc * inv)) * inv */
return fp_mul((acc_squared - fp_mul(fp_sq(acc), inv)), inv);
}
bool still_det_update(struct still_det *still_det, uint32_t sample_time,
fp_t x, fp_t y, fp_t z)
{
fp_t inv = FLOAT_TO_FP(0.0f), var_x, var_y, var_z;
bool complete = false;
/* Accumulate for mean and VAR */
still_det->acc_x += x;
still_det->acc_y += y;
still_det->acc_z += z;
still_det->acc_xx += fp_mul(x, x);
still_det->acc_yy += fp_mul(y, y);
still_det->acc_zz += fp_mul(z, z);
switch (++still_det->num_samples) {
case 0:
/* If we rolled over, go back. */
still_det->num_samples--;
break;
case 1:
/* Set a new start time if new batch. */
still_det->window_start_time = sample_time;
break;
}
if (stillness_batch_complete(still_det, sample_time)) {
/*
* Compute 1/num_samples and check for num_samples == 0 (should
* never happen, but just in case)
*/
if (still_det->num_samples) {
inv = fp_div(1.0f, INT_TO_FP(still_det->num_samples));
} else {
still_det_reset(still_det);
return complete;
}
/* Calculating the VAR = sum(x^2)/n - sum(x)^2/n^2 */
var_x = compute_variance(
still_det->acc_xx, still_det->acc_x, inv);
var_y = compute_variance(
still_det->acc_yy, still_det->acc_y, inv);
var_z = compute_variance(
still_det->acc_zz, still_det->acc_z, inv);
/* Checking if sensor is still */
if (var_x < still_det->var_threshold &&
var_y < still_det->var_threshold &&
var_z < still_det->var_threshold) {
still_det->mean_x = fp_mul(still_det->acc_x, inv);
still_det->mean_y = fp_mul(still_det->acc_y, inv);
still_det->mean_z = fp_mul(still_det->acc_z, inv);
complete = true;
}
/* Reset and start over */
still_det_reset(still_det);
}
return complete;
}
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