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45 lines
1.6 KiB
45 lines
1.6 KiB
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// for random()
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#include <stdlib.h>
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#include "TimestampScheduler.h"
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using namespace aaudio;
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void TimestampScheduler::start(int64_t startTime) {
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mStartTime = startTime;
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mLastTime = startTime;
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}
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int64_t TimestampScheduler::nextAbsoluteTime() {
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int64_t periodsElapsed = (mLastTime - mStartTime) / mBurstPeriod;
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// This is an arbitrary schedule that could probably be improved.
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// It starts out sending a timestamp on every period because we want to
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// get an accurate picture when the stream starts. Then it slows down
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// to the occasional timestamps needed to detect a slow drift.
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int64_t minPeriodsToDelay = (periodsElapsed < 10) ? 1 :
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(periodsElapsed < 100) ? 3 :
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(periodsElapsed < 1000) ? 10 : 50;
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int64_t sleepTime = minPeriodsToDelay * mBurstPeriod;
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// Generate a random rectangular distribution one burst wide so that we get
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// an uncorrelated sampling of the MMAP pointer.
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sleepTime += (int64_t)(random() * mBurstPeriod / RAND_MAX);
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mLastTime += sleepTime;
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return mLastTime;
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}
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