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 24 void TimestampScheduler::start(int64_t startTime) { 25 mStartTime = startTime; 26 mLastTime = startTime; 27 } 28 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
