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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.
*/
// for random()
#include <stdlib.h>
#include "TimestampScheduler.h"
using namespace aaudio;
void TimestampScheduler::start(int64_t startTime) {
mStartTime = startTime;
mLastTime = startTime;
}
int64_t TimestampScheduler::nextAbsoluteTime() {
int64_t periodsElapsed = (mLastTime - mStartTime) / mBurstPeriod;
// This is an arbitrary schedule that could probably be improved.
// It starts out sending a timestamp on every period because we want to
// get an accurate picture when the stream starts. Then it slows down
// to the occasional timestamps needed to detect a slow drift.
int64_t minPeriodsToDelay = (periodsElapsed < 10) ? 1 :
(periodsElapsed < 100) ? 3 :
(periodsElapsed < 1000) ? 10 : 50;
int64_t sleepTime = minPeriodsToDelay * mBurstPeriod;
// Generate a random rectangular distribution one burst wide so that we get
// an uncorrelated sampling of the MMAP pointer.
sleepTime += (int64_t)(random() * mBurstPeriod / RAND_MAX);
mLastTime += sleepTime;
return mLastTime;
}