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
22using namespace aaudio;
23
24void TimestampScheduler::start(int64_t startTime) {
25    mStartTime = startTime;
26    mLastTime = startTime;
27}
28
29int64_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