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Diffstat (limited to 'media/libstagefright/wifi-display/TimeSyncer.h')
-rw-r--r-- | media/libstagefright/wifi-display/TimeSyncer.h | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/media/libstagefright/wifi-display/TimeSyncer.h b/media/libstagefright/wifi-display/TimeSyncer.h new file mode 100644 index 0000000..0e3aed7 --- /dev/null +++ b/media/libstagefright/wifi-display/TimeSyncer.h @@ -0,0 +1,109 @@ +/* + * Copyright 2013, 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. + */ + +#ifndef TIME_SYNCER_H_ + +#define TIME_SYNCER_H_ + +#include <media/stagefright/foundation/AHandler.h> + +namespace android { + +struct ANetworkSession; + +/* + TimeSyncer allows us to synchronize time between a client and a server. + The client sends a UDP packet containing its send-time to the server, + the server sends that packet back to the client amended with information + about when it was received as well as the time the reply was sent back. + Finally the client receives the reply and has now enough information to + compute the clock offset between client and server assuming that packet + exchange is symmetric, i.e. time for a packet client->server and + server->client is roughly equal. + This exchange is repeated a number of times and the average offset computed + over the 30% of packets that had the lowest roundtrip times. + The offset is determined every 10 secs to account for slight differences in + clock frequency. +*/ +struct TimeSyncer : public AHandler { + enum { + kWhatError, + kWhatTimeOffset, + }; + TimeSyncer( + const sp<ANetworkSession> &netSession, + const sp<AMessage> ¬ify); + + void startServer(unsigned localPort); + void startClient(const char *remoteHost, unsigned remotePort); + +protected: + virtual ~TimeSyncer(); + + virtual void onMessageReceived(const sp<AMessage> &msg); + +private: + enum { + kWhatStartServer, + kWhatStartClient, + kWhatUDPNotify, + kWhatSendPacket, + kWhatTimedOut, + }; + + struct TimeInfo { + int64_t mT1; // client timestamp at send + int64_t mT2; // server timestamp at receive + int64_t mT3; // server timestamp at send + int64_t mT4; // client timestamp at receive + }; + + enum { + kNumPacketsPerBatch = 30, + }; + static const int64_t kTimeoutDelayUs = 500000ll; + static const int64_t kBatchDelayUs = 10000000ll; // every 10 secs + + sp<ANetworkSession> mNetSession; + sp<AMessage> mNotify; + + bool mIsServer; + bool mConnected; + int32_t mUDPSession; + uint32_t mSeqNo; + double mTotalTimeUs; + + Vector<TimeInfo> mHistory; + + int64_t mPendingT1; + int32_t mTimeoutGeneration; + + void postSendPacket(int64_t delayUs = 0ll); + + void postTimeout(); + void cancelTimeout(); + + void notifyError(status_t err); + void notifyOffset(); + + static int CompareRountripTime(const TimeInfo *ti1, const TimeInfo *ti2); + + DISALLOW_EVIL_CONSTRUCTORS(TimeSyncer); +}; + +} // namespace android + +#endif // TIME_SYNCER_H_ |