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/*
* 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;
/**
* 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 monotonic clock 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 is 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_remote + 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 static long microTime() {
return System.nanoTime() / 1000;
}
public long micros() {
return microTime() - baseTime;
}
public int getMeanLag() {
return (minLag + maxLag) / 2;
}
public String toString() {
return "Remote clock [us]: current time = " + micros() + " baseTime = " + baseTime +
" lagBounds = (" + minLag + ", " + maxLag + ")";
}
}
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