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 
17 // for random()
18 #include <stdlib.h>
19 
20 #include "TimestampScheduler.h"
21 
22 using namespace aaudio;
23 
start(int64_t startTime)24 void TimestampScheduler::start(int64_t startTime) {
25     mStartTime = startTime;
26     mLastTime = startTime;
27 }
28 
nextAbsoluteTime()29 int64_t TimestampScheduler::nextAbsoluteTime() {
30     int64_t periodsElapsed = (mLastTime - mStartTime) / mBurstPeriod;
31     // This is an arbitrary schedule that could probably be improved.
32     // It starts out sending a timestamp on every period because we want to
33     // get an accurate picture when the stream starts. Then it slows down
34     // to the occasional timestamps needed to detect a slow drift.
35     int64_t minPeriodsToDelay = (periodsElapsed < 10) ? 1 :
36         (periodsElapsed < 100) ? 3 :
37         (periodsElapsed < 1000) ? 10 : 50;
38     int64_t sleepTime = minPeriodsToDelay * mBurstPeriod;
39     // Generate a random rectangular distribution one burst wide so that we get
40     // an uncorrelated sampling of the MMAP pointer.
41     sleepTime += (int64_t)(random() * mBurstPeriod / RAND_MAX);
42     mLastTime += sleepTime;
43     return mLastTime;
44 }
45