1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
/*
* Copyright (C) 2016 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.
*/
package org.chromium.latency.walt;
import android.util.Log;
import java.lang.reflect.Method;
/**
* Representation of our best knowledge of the remote clock.
* All time variables here are stored in microseconds.
*
* Which time reporting function is used locally on Android:
* This app uses SystemClock.uptimeMillis() for keeping local time which, up to
* units, is the same time reported by System.nanoTime() and by
* clock_gettime(CLOCK_MONOTONIC, &ts) from time.h and is, roughly, the time
* elapsed since last boot, excluding sleep time.
*
* base_time is the local Android time when remote clock was zeroed.
*
* micros() is our best available approximation of the current reading of the remote clock.
*
* Immediately after synchronization minLag is set to zero and the remote clock guaranteed to lag
* behind what micros() reports by at most maxLag.
*
* Immediately after synchronization or an update of the bounds (minLag, maxLag) the following holds
* t_remote + minLag < micros() < t_rmote + maxLag
*
* For more details about clock synchronization refer to
* https://github.com/google/walt/blob/master/android/WALT/app/src/main/jni/README.md
* and sync_clock.c
*/
public class RemoteClockInfo {
public int minLag;
public int maxLag;
public long baseTime;
public long micros() {
return microTime() - baseTime;
}
public static long microTime() {
return System.nanoTime() / 1000;
}
/**
Find the wall time when uptime was zero = CLOCK_REALTIME - CLOCK_MONOTONIC
Needed for TCP bridge because Python prior to 3.3 has no direct access to CLOCK_MONOTONIC
so the bridge returns timestamps as wall time and we need to convert them to CLOCK_MONOTONIC.
See:
[1] https://docs.python.org/3/library/time.html#time.CLOCK_MONOTONIC
[2] http://stackoverflow.com/questions/14270300/what-is-the-difference-between-clock-monotonic-clock-monotonic-raw
[3] http://stackoverflow.com/questions/1205722/how-do-i-get-monotonic-time-durations-in-python
android.os.SystemClock.currentTimeMicros() is hidden by @hide which means it can't be called
directly - calling it via reflection.
See:
http://stackoverflow.com/questions/17035271/what-does-hide-mean-in-the-android-source-code
*/
public static long uptimeZero() {
long t = -1;
long dt = Long.MAX_VALUE;
try {
Class cls = Class.forName("android.os.SystemClock");
Method myTimeGetter = cls.getMethod("currentTimeMicro");
t = (long) myTimeGetter.invoke(null);
dt = t - microTime();
} catch (Exception e) {
Log.i("WALT.uptimeZero", e.getMessage());
}
return dt;
}
public static long currentTimeMicro() {
long t = -1;
try {
Class cls = Class.forName("android.os.SystemClock");
Method myTimeGetter = cls.getMethod("currentTimeMicro");
t = (long) myTimeGetter.invoke(null);
} catch (Exception e) {
Log.i("WALT.currentTimeMicro", e.getMessage());
}
return t;
}
public int getMeanLag() {
return (minLag + maxLag) / 2;
}
public String toString(){
return "Remote clock [us]: current time = " + micros() + " baseTime = " + baseTime +
" lagBounds = (" + minLag + ", " + maxLag + ")";
}
}
|
