1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "calibration/sample_rate_estimator/sample_rate_estimator.h"
18
19 #include <string.h>
20
21 #include "common/math/macros.h"
22 #include "util/nano_assert.h"
23
24 // Helper function used to reset the sampling rate estimator accumulator.
sampleRateEstimatorResetAccumulator(struct SampleRateEstimator * sample_rate_estimator)25 static void sampleRateEstimatorResetAccumulator(
26 struct SampleRateEstimator* sample_rate_estimator) {
27 sample_rate_estimator->last_timestamp_nanos = 0.0f;
28 sample_rate_estimator->interval_accumulator_nanos = 0.0f;
29 sample_rate_estimator->num_intervals_collected = 0;
30 }
31
sampleRateEstimatorInit(struct SampleRateEstimator * sample_rate_estimator,size_t num_intervals_to_collect,float max_interval_sec)32 void sampleRateEstimatorInit(struct SampleRateEstimator* sample_rate_estimator,
33 size_t num_intervals_to_collect,
34 float max_interval_sec) {
35 ASSERT_NOT_NULL(sample_rate_estimator);
36 memset(sample_rate_estimator, 0, sizeof(struct SampleRateEstimator));
37 sample_rate_estimator->mean_sampling_rate_estimate_hz =
38 SAMPLE_RATE_ESTIMATOR_INVALID_SAMPLE_RATE_HZ;
39 sample_rate_estimator->num_intervals_to_collect = num_intervals_to_collect;
40 sample_rate_estimator->max_interval_nanos =
41 max_interval_sec * SEC_TO_NANOS(1);
42 }
43
sampleRateEstimatorGetHz(struct SampleRateEstimator * sample_rate_estimator)44 float sampleRateEstimatorGetHz(
45 struct SampleRateEstimator* sample_rate_estimator) {
46 sample_rate_estimator->new_sampling_rate_estimate_ready = false;
47 return sample_rate_estimator->mean_sampling_rate_estimate_hz;
48 }
49
sampleRateEstimatorUpdate(struct SampleRateEstimator * sample_rate_estimator,uint64_t timestamp_nanos)50 void sampleRateEstimatorUpdate(
51 struct SampleRateEstimator* sample_rate_estimator,
52 uint64_t timestamp_nanos) {
53 // Resets the current interval capture and returns if:
54 // 1. A bad timestamp was received (i.e., time not monotonic).
55 // 2. 'last_timestamp_nanos' is zero. NOTE: 'last_timestamp_nanos' = 0
56 // indicates that the first complete time interval has not been captured
57 // yet (so, set it and return).
58 if (timestamp_nanos <= sample_rate_estimator->last_timestamp_nanos ||
59 sample_rate_estimator->last_timestamp_nanos == 0) {
60 sample_rate_estimator->last_timestamp_nanos = timestamp_nanos;
61 return;
62 }
63
64 // Computes the current sampling interval. This conversion will be very fast
65 // for intervals less than ~4.3 seconds (i.e., 2^32 nano-seconds).
66 const float next_interval_nanos = floatFromUint64(
67 timestamp_nanos - sample_rate_estimator->last_timestamp_nanos);
68
69 // Helps prevent corruption of the estimator when there are gaps in the input
70 // sampling intervals greater than 'max_interval_nanos' (i.e., intermittant
71 // periods where there are no input timestamps).
72 if (next_interval_nanos >= sample_rate_estimator->max_interval_nanos) {
73 // Resets the estimator and returns.
74 sampleRateEstimatorResetAccumulator(sample_rate_estimator);
75 return;
76 }
77
78 // Accumulates the next sampling interval.
79 sample_rate_estimator->interval_accumulator_nanos += next_interval_nanos;
80 sample_rate_estimator->last_timestamp_nanos = timestamp_nanos;
81 sample_rate_estimator->num_intervals_collected++;
82
83 // If the number of collected time intervals exceed the target number, then
84 // this computes a new sample rate estimate.
85 if (sample_rate_estimator->num_intervals_collected >
86 sample_rate_estimator->num_intervals_to_collect) {
87 sample_rate_estimator->mean_sampling_rate_estimate_hz =
88 sample_rate_estimator->num_intervals_collected *
89 (SEC_TO_NANOS(1) / sample_rate_estimator->interval_accumulator_nanos);
90
91 // Sets the polling flag to indicate that a new estimate is ready.
92 sample_rate_estimator->new_sampling_rate_estimate_ready = true;
93
94 // Resets the estimator variables.
95 sampleRateEstimatorResetAccumulator(sample_rate_estimator);
96 }
97 }
98