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/*
* Copyright (C) 2018 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.
*/
#include "calibration/sample_rate_estimator/sample_rate_estimator.h"
#include <string.h>
#include "common/math/macros.h"
#include "chre/util/nanoapp/assert.h"
// Helper function used to reset the sampling rate estimator accumulator.
static void sampleRateEstimatorResetAccumulator(
struct SampleRateEstimator* sample_rate_estimator) {
sample_rate_estimator->last_timestamp_nanos = 0.0f;
sample_rate_estimator->interval_accumulator_nanos = 0.0f;
sample_rate_estimator->num_intervals_collected = 0;
}
void sampleRateEstimatorInit(struct SampleRateEstimator* sample_rate_estimator,
size_t num_intervals_to_collect,
float max_interval_sec) {
CHRE_ASSERT_NOT_NULL(sample_rate_estimator);
memset(sample_rate_estimator, 0, sizeof(struct SampleRateEstimator));
sample_rate_estimator->mean_sampling_rate_estimate_hz =
SAMPLE_RATE_ESTIMATOR_INVALID_SAMPLE_RATE_HZ;
sample_rate_estimator->num_intervals_to_collect = num_intervals_to_collect;
sample_rate_estimator->max_interval_nanos =
max_interval_sec * SEC_TO_NANOS(1);
}
float sampleRateEstimatorGetHz(
struct SampleRateEstimator* sample_rate_estimator) {
sample_rate_estimator->new_sampling_rate_estimate_ready = false;
return sample_rate_estimator->mean_sampling_rate_estimate_hz;
}
void sampleRateEstimatorUpdate(
struct SampleRateEstimator* sample_rate_estimator,
uint64_t timestamp_nanos) {
// Resets the current interval capture and returns if:
// 1. A bad timestamp was received (i.e., time not monotonic).
// 2. 'last_timestamp_nanos' is zero. NOTE: 'last_timestamp_nanos' = 0
// indicates that the first complete time interval has not been captured
// yet (so, set it and return).
if (timestamp_nanos <= sample_rate_estimator->last_timestamp_nanos ||
sample_rate_estimator->last_timestamp_nanos == 0) {
sample_rate_estimator->last_timestamp_nanos = timestamp_nanos;
return;
}
// Computes the current sampling interval. This conversion will be very fast
// for intervals less than ~4.3 seconds (i.e., 2^32 nano-seconds).
const float next_interval_nanos = floatFromUint64(
timestamp_nanos - sample_rate_estimator->last_timestamp_nanos);
// Helps prevent corruption of the estimator when there are gaps in the input
// sampling intervals greater than 'max_interval_nanos' (i.e., intermittant
// periods where there are no input timestamps).
if (next_interval_nanos >= sample_rate_estimator->max_interval_nanos) {
// Resets the estimator and returns.
sampleRateEstimatorResetAccumulator(sample_rate_estimator);
return;
}
// Accumulates the next sampling interval.
sample_rate_estimator->interval_accumulator_nanos += next_interval_nanos;
sample_rate_estimator->last_timestamp_nanos = timestamp_nanos;
sample_rate_estimator->num_intervals_collected++;
// If the number of collected time intervals exceed the target number, then
// this computes a new sample rate estimate.
if (sample_rate_estimator->num_intervals_collected >
sample_rate_estimator->num_intervals_to_collect) {
sample_rate_estimator->mean_sampling_rate_estimate_hz =
sample_rate_estimator->num_intervals_collected *
(SEC_TO_NANOS(1) / sample_rate_estimator->interval_accumulator_nanos);
// Sets the polling flag to indicate that a new estimate is ready.
sample_rate_estimator->new_sampling_rate_estimate_ready = true;
// Resets the estimator variables.
sampleRateEstimatorResetAccumulator(sample_rate_estimator);
}
}
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