1/*
2 * Copyright (C) 2016 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
17package org.chromium.latency.walt;
18
19/**
20 * Representation of our best knowledge of the remote clock.
21 * All time variables here are stored in microseconds.
22 *
23 * Which time reporting function is used locally on Android:
24 * This app uses SystemClock.uptimeMillis() for keeping local time which, up to
25 * units, is the same time reported by System.nanoTime() and by
26 * clock_gettime(CLOCK_MONOTONIC, &ts) from time.h and is, roughly, the time
27 * elapsed since last boot, excluding sleep time.
28 *
29 * base_time is the local monotonic clock time when remote clock was zeroed.
30 *
31 * micros() is our best available approximation of the current reading of the remote clock.
32 *
33 * Immediately after synchronization, minLag is set to zero and the remote clock is guaranteed to
34 * lag behind what micros() reports by at most maxLag.
35 *
36 * Immediately after synchronization or an update of the bounds (minLag, maxLag) the following holds
37 * t_remote + minLag < micros() < t_remote + maxLag
38 *
39 * For more details about clock synchronization refer to
40 * https://github.com/google/walt/blob/master/android/WALT/app/src/main/jni/README.md
41 * and sync_clock.c
42 */
43
44public class RemoteClockInfo {
45    public int minLag;
46    public int maxLag;
47    public long baseTime;
48
49    public static long microTime() {
50        return System.nanoTime() / 1000;
51    }
52
53    public long micros() {
54        return microTime() - baseTime;
55    }
56
57    public int getMeanLag() {
58        return (minLag + maxLag) / 2;
59    }
60
61    public String toString() {
62        return "Remote clock [us]: current time = " + micros() + " baseTime = " + baseTime +
63                " lagBounds = (" + minLag + ", " + maxLag + ")";
64    }
65}
66