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Tower 实战一：MavLink的连接与通信
1 废话不多说，Tower的连接方式之一是通过android通过手机自带蓝牙模块，和遥控器蓝牙通信，最后在连接飞空，飞空是一块单片机，里面也有一套程序处理逻辑，然后遥控器坐传输媒介
这样做的好处就是把一些用户操作放到android上面，比如航点规划，客服端控制飞机的起飞，降落等，最后飞空来控制无人机玩成一系列的操作
连接方式如图
2 今天主要说一下Mavlink的连接首先在Tower的源码里构建了一个类
public class MAVLinkClient implements MAVLinkStreams.MAVLinkOutputStream { public MAVLinkClient(Context context, MAVLinkStreams.MavlinkInputStream listener) { this.listener = listener; } private void connectMAVConnection() { } public void sendMavPacket(MAVLinkPacket pack) { } @Override public void toggleConnectionState() { if (isConnected()) { closeConnection(); } else { openConnection(); } } }
这个了主要实习了 连接，切换连接，发送数据包，和注入一个listener ， 这个listener主要是接受到数据的时候回调，所以这个类主要就是实习这个几个功能，Tower向无人机发送数据基本都是通过这个sendMavPacket方法去实现的
3 我们看看listener是个什么东西
public interface MavlinkInputStream { void notifyConnected(); void notifyDisconnected(); void notifyReceivedData(MAVLinkMessage m); }
这个listener的声明 ，他是用来处理收到消息的 ，调用notifyReceivedData 接受一个MavLinkmessage
4 接来我们看MavLinkClient的初始化，差看源码可以看到，在Application的初始化OnCreatef 方法里面 MAVLinkClient MAVClient = new MAVLinkClient(this, this); 可以看到Application 实现了MavlinkInputStream 接口，并且实现了 notifyReceivedData 方法
@Override public void notifyReceivedData(MAVLinkMessage msg) { mavLinkMsgHandler.receiveData(msg); }
5 这样你就很容易看到在哪里处理 MAVLinkMessage 了，so ， MavLinkMsgHandler 就是 MAVLinkMessage 的处类了，你可以看到关于多种MAVLinkMessage 的处理，这些消息有心跳消息，事件消息等。。。
6 现在条理是不是很清楚了，那我们就来看android如果通过蓝牙连接飞控的，首先你必须会蓝牙连接的基础知识，网上资料很多
7 我们看连接函数
private void connectMAVConnection() { bluetoothConnection.addMavLinkConnectionListener("blue",mConnectionListener); Toast.makeText(parent, R.string.status_connecting, Toast.LENGTH_SHORT).show(); if (bluetoothConnection.getConnectionStatus() == MavLinkConnection.MAVLINK_DISCONNECTED) { bluetoothConnection.connect(); } }
直接调用了bluetoothConnection.connect(), MavLinkConnection bluetoothConnection是一个抽象类，也住无人机地面站里面的一个比较核心的类，
/** * Listen for incoming data on the mavlink connection. */ private final Runnable mConnectingTask = new Runnable() { @Override public void run() { Thread sendingThread = null, loggingThread = null; try { // Open the connection openConnection(); mConnectionStatus.set(MAVLINK_CONNECTED); // Launch the ‘Sending‘, and ‘Logging‘ threads sendingThread = new Thread(mSendingTask, "MavLinkConnection-Sending Thread"); sendingThread.start(); final Parser parser = new Parser(); parser.stats.mavlinkResetStats(); final byte[] readBuffer = new byte[READ_BUFFER_SIZE]; while (mConnectionStatus.get() == MAVLINK_CONNECTED&&!isAndroidfor4_4()) { int bufferSize = readDataBlock(readBuffer); if (readBuffer==null||readBuffer.length==0){ continue; } handleData(parser, bufferSize, readBuffer); } } catch (Exception e) { Log.i("===>>","disconent"); if (loggingThread != null && loggingThread.isAlive()) { loggingThread.interrupt(); } if (sendingThread != null && sendingThread.isAlive()) { sendingThread.interrupt(); } mConnectionStatus.set(MAVLINK_DISCONNECTED); disconnect(); } }
8 这个类有几个核心的方法 1打开连接 openConnection（），2 sendingThread不停地发送数据 3 handleData（）处理数据，在其实现类里面主要也是完成这3个方法，
public Bluetoothfor2_0Connection(Context parentContext) { prefs = new DroidPlannerPrefs(parentContext); mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); if (mBluetoothAdapter == null) { Log.d(BLUE, "Null adapters"); } } protected void openAndroidConnection() throws IOException { Log.d(BLUE, "Connect"); // Reset the bluetooth connection resetConnection(); // Retrieve the stored device BluetoothDevice device = null; final String addressName = prefs.getBluetoothDeviceAddress(); if (addressName != null) { // strip name, use address part - stored as <address>;<name> final String part[] = addressName.split(";"); try { device = mBluetoothAdapter.getRemoteDevice(part[0]); } catch (IllegalArgumentException ex) { // invalid configuration (device may have been removed) // NOP fall through to ‘no device‘ } } // no device if (device == null) device = findSerialBluetoothBoard(); Log.d(BLUE, "Trying to connect to device with address " + device.getAddress()); Log.d(BLUE, "BT Create Socket Call..."); bluetoothSocket = device.createInsecureRfcommSocketToServiceRecord(UUID .fromString(UUID_SPP_DEVICE)); Log.d(BLUE, "BT Cancel Discovery Call..."); mBluetoothAdapter.cancelDiscovery(); Log.d(BLUE, "BT Connect Call..."); bluetoothSocket.connect(); // Here the IOException will rise on BT // protocol/handshake error. Log.d(BLUE, "## BT Connected ##"); out = bluetoothSocket.getOutputStream(); in = bluetoothSocket.getInputStream(); } @Override protected int readDataBlock(byte[] buffer) throws IOException { return in.read(buffer); } @Override protected void sendBuffer(byte[] buffer) throws IOException { if (out != null) { out.write(buffer); } }
9 handledata 方法就是回调之前的 listener.notifydatareceiver(),是不是之前地方了，至于发送数据
private final Runnable mSendingTask = new Runnable() { @Override public void run() { int msgSeqNumber = 0; try { while (mConnectionStatus.get() == MAVLINK_CONNECTED) { final MAVLinkPacket packet = mPacketsToSend.take(); packet.seq = msgSeqNumber; byte[] buffer = packet.encodePacket(); if (buffer==null|| buffer.length==0){ continue; } try { sendBuffer(buffer); queueToLog(packet); } catch (IOException e) { reportComError(e.getMessage()); mLogger.logErr(TAG, e); } msgSeqNumber = (msgSeqNumber + 1) % (MAX_PACKET_SEQUENCE + 1); } } catch (InterruptedException e) { };
发送数据其实也是Mavclient的 sendMavPacket方法，里面有一个阻塞队列的东西，线程安全的双端队列，可能需要你看看，思路很清晰，2可能会讲 MavlinkMessage
@Override public void sendMavPacket(MAVLinkPacket pack) { if (!isConnected()) { return; } bluetoothConnection.sendMavPacket(pack); }
Tower 实战一：MavLink的连接与通信