Android与蓝牙耳机建立连接的分析

Android 实现了对Headset 和Handsfree 两种profile 的支持。其实现核心是BluetoothHeadsetService，在PhoneApp 创建的时候会启动它。

if (getSystemService(Context.BLUETOOTH_SERVICE) != null) {

mBtHandsfree = new BluetoothHandsfree(this, phone);

startService(new Intent(this, BluetoothHeadsetService.class));

} else {

// Device is not bluetooth capable

mBtHandsfree = null;

}

BluetoothHeadsetService 通过接收ENABLED_ACTION、BONDING_CREATED_ACTION 、DISABLED_ACTION 和REMOTE_DEVICE_DISCONNECT_REQUESTEDACTION 来改变状态，它也会监听Phone 的状态变化。

IntentFilter filter = new IntentFilter(BluetoothIntent.BONDING_CREATED_ACTION);

filter.addAction(BluetoothIntent.REMOTE_DEVICE_DISCONNECT_REQUESTED_ACTION);

filter.addAction(BluetoothIntent.ENABLED_ACTION);

filter.addAction(BluetoothIntent.DISABLED_ACTION);

registerReceiver(mBluetoothIntentReceiver, filter);

mPhone.registerForPhoneStateChanged(mStateChangeHandler,PHONE_STATE_CHANGED, null);

BluetoothHeadsetService 收到ENABLED_ACTION时，会先向BlueZ注册Headset 和Handsfree 两种profile（通过执行sdptool 来实现的，均作为Audio Gateway），然后让BluetoothAudioGateway 接收RFCOMM 连接，让BluetoothHandsfree 接收SCO连接（这些操作都是为了让蓝牙耳机能主动连上Android）。

if (action.equals(BluetoothIntent.ENABLED_ACTION)) {

// SDP server may not be ready, so wait 3 seconds before

// registering records.

// TODO: Use a different mechanism to register SDP records,

// that actually ACK’s on success, so that we can retry rather

// than hardcoding a 3 second guess.

mHandler.sendMessageDelayed(mHandler.obtainMessage(REGISTER_SDP_RECORDS),3000);

mAg.start(mIncomingConnectionHandler);

mBtHandsfree.onBluetoothEnabled();

}

BluetoothHeadsetService 收到DISABLED_ACTION 时，会停止BluetoothAudioGateway 和BluetoothHandsfree。

if (action.equals(BluetoothIntent.DISABLED_ACTION)) {

mBtHandsfree.onBluetoothDisabled();

mAg.stop();

}

Android 跟蓝牙耳机建立连接有两种方式。

1. Android 主动跟蓝牙耳机连BluetoothSettings 中和蓝牙耳机配对上之后， BluetoothHeadsetService 会收到BONDING_CREATED_ACTION，这个时候BluetoothHeadsetService 会主动去和蓝牙耳机建立RFCOMM 连接。

if (action.equals(BluetoothIntent.BONDING_CREATED_ACTION)) {

if (mState == BluetoothHeadset.STATE_DISCONNECTED) {

// Lets try and initiate an RFCOMM connection

try {

mBinder.connectHeadset(address, null);

} catch (RemoteException e) {}

}

}

RFCOMM 连接的真正实现是在ConnectionThread 中，它分两步，第一步先通过SDPClient 查询蓝牙设备时候支持Headset 和Handsfree profile。

// 1) SDP query

SDPClient client = SDPClient.getSDPClient(address);

if (DBG) log(”Connecting to SDP server (” + address + “)…”);

if (!client.connectSDPAsync()) {

Log.e(TAG, “Failed to start SDP connection to ” + address);

mConnectingStatusHandler.obtainMessage(SDP_ERROR).sendToTarget();

client.disconnectSDP();

return;

}

if (isInterrupted()) {

client.disconnectSDP();

return;

}

if (!client.waitForSDPAsyncConnect(20000)) { // 20 secs

if (DBG) log(”Failed to make SDP connection to ” + address);

mConnectingStatusHandler.obtainMessage(SDP_ERROR).sendToTarget();

client.disconnectSDP();

return;

}

if (DBG) log(”SDP server connected (” + address + “)”);

int headsetChannel = client.isHeadset();

if (DBG) log(”headset channel = ” + headsetChannel);

int handsfreeChannel = client.isHandsfree();

if (DBG) log(”handsfree channel = ” + handsfreeChannel);

client.disconnectSDP();

第2步才是去真正建立RFCOMM 连接。

// 2) RFCOMM connect

mHeadset = new HeadsetBase(mBluetooth, address, channel);

if (isInterrupted()) {

return;

}

int result = mHeadset.waitForAsyncConnect(20000, // 20 secs

mConnectedStatusHandler);

if (DBG) log(”Headset RFCOMM connection attempt took ” +(System.currentTimeMillis() – timestamp) + ” ms”);

if (isInterrupted()) {

return;

}

if (result < 0) {

Log.e(TAG, “mHeadset.waitForAsyncConnect() error: ” + result);

mConnectingStatusHandler.obtainMessage(RFCOMM_ERROR).sendToTarget();

return;

} else if (result == 0) {

Log.e(TAG, “mHeadset.waitForAsyncConnect() error: ” + result +”(timeout)”);

mConnectingStatusHandler.obtainMessage(RFCOMM_ERROR).sendToTarget();

return;

} else {

if (DBG) log(”mHeadset.waitForAsyncConnect() success”);

mConnectingStatusHandler.obtainMessage(RFCOMM_CONNECTED).sendToTarget();

}

当RFCOMM连接成功建立后，BluetoothHeadsetDevice 会收到RFCOMM_CONNECTED消息，它会调用BluetoothHandsfree 来建立SCO 连接，广播通知Headset状态变化的Intent（PhoneApp 和BluetoothSettings 会接收这个Intent）。

case RFCOMM_CONNECTED:

// success

if (DBG) log(”Rfcomm connected”);

if (mConnectThread != null) {

try {

mConnectThread.join();

} catch (InterruptedException e) {

Log.w(TAG, “Connect attempt cancelled, ignoring

RFCOMM_CONNECTED”, e);

return;

}

mConnectThread = null;

}

setState(BluetoothHeadset.STATE_CONNECTED,BluetoothHeadset.RESULT_SUCCESS);

mBtHandsfree.connectHeadset(mHeadset, mHeadsetType);

break;

BluetoothHandsfree 会先做一些初始化工作，比如根据是Headset 还是Handsfree 初始化不同的ATParser，并且启动一个接收线程从已建立的RFCOMM上接收蓝牙耳机过来的控制命令（也就是AT 命令），接着判断如果是在打电话过程中，才去建立SCO 连接来打通数据通道。

/* package */

void connectHeadset(HeadsetBase headset, int headsetType) {

mHeadset = headset;

mHeadsetType = headsetType;

if (mHeadsetType == TYPE_HEADSET) {

initializeHeadsetAtParser();

} else {

initializeHandsfreeAtParser();

}

headset.startEventThread();

configAudioParameters();

if (inDebug()) {

startDebug();

}

if (isIncallAudio()) {

audioOn();

}

}

建立SCO 连接是通过SCOSocket 实现的

/** Request to establish SCO (audio) connection to bluetooth

* headset/handsfree, if one is connected. Does not block.

* Returns false if the user has requested audio off, or if there

* is some other immediate problem that will prevent BT audio.

*/

/* package */

synchronized boolean audioOn() {

mOutgoingSco = createScoSocket();

if (!mOutgoingSco.connect(mHeadset.getAddress())) {

mOutgoingSco = null;

}

return true;

}

当SCO 连接成功建立后，BluetoothHandsfree 会收到SCO_CONNECTED 消息，它就会去调用AudioManager 的setBluetoothScoOn函数，从而通知音频系统有个蓝牙耳机可用了。

到此，Android 完成了和蓝牙耳机的全部连接。

case SCO_CONNECTED:

if (msg.arg1 == ScoSocket.STATE_CONNECTED && isHeadsetConnected()&&mConnectedSco == null) {

if (DBG) log(”Routing audio for outgoing SCO conection”);

mConnectedSco = (ScoSocket)msg.obj;

mAudioManager.setBluetoothScoOn(true);

} else if (msg.arg1 == ScoSocket.STATE_CONNECTED) {

if (DBG) log(”Rejecting new connected outgoing SCO socket”);

((ScoSocket)msg.obj).close();

mOutgoingSco.close();

}

mOutgoingSco = null;

break;

2. 蓝牙耳机主动跟Android 连首先BluetoothAudioGateway 会在一个线程中收到来自蓝牙耳机的RFCOMM 连接，然后发送消息给BluetoothHeadsetService。

mConnectingHeadsetRfcommChannel = -1;

mConnectingHandsfreeRfcommChannel = -1;

if(waitForHandsfreeConnectNative(SELECT_WAIT_TIMEOUT) == false) {

if (mTimeoutRemainingMs > 0) {

try {

Log.i(tag, “select thread timed out, but ” +

mTimeoutRemainingMs + “ms of

waiting remain.”);

Thread.sleep(mTimeoutRemainingMs);

} catch (InterruptedException e) {

Log.i(tag, “select thread was interrupted (2),

exiting”);

mInterrupted = true;

}

}

}

BluetoothHeadsetService 会根据当前的状态来处理消息，分3 种情况，第一是当前状态是非连接状态，会发送RFCOMM_CONNECTED 消息，后续处理请参见前面的分析。

case BluetoothHeadset.STATE_DISCONNECTED:

// headset connecting us, lets join

setState(BluetoothHeadset.STATE_CONNECTING);

mHeadsetAddress = info.mAddress;

mHeadset = new HeadsetBase(mBluetooth, mHeadsetAddress,info.mSocketFd,info.mRfcommChan,mConnectedStatusHandler);

mHeadsetType = type;

mConnectingStatusHandler.obtainMessage(RFCOMM_CONNECTED).sendToTarget();

break;

如果当前是正在连接状态， 则先停掉已经存在的ConnectThread，并直接调用BluetoothHandsfree 去建立SCO 连接。

case BluetoothHeadset.STATE_CONNECTING:

// If we are here, we are in danger of a race condition

// incoming rfcomm connection, but we are also attempting an

// outgoing connection. Lets try and interrupt the outgoing

// connection.

mConnectThread.interrupt();

// Now continue with new connection, including calling callback

mHeadset = new HeadsetBase(mBluetooth,mHeadsetAddress,info.mSocketFd,info.mRfcommChan,mConnectedStatusHandler);

mHeadsetType = type;

setState(BluetoothHeadset.STATE_CONNECTED,BluetoothHeadset.RESULT_SUCCESS);

mBtHandsfree.connectHeadset(mHeadset,mHeadsetType);

// Make sure that old outgoing connect thread is dead.

break;

如果当前是已连接的状态，这种情况是一种错误case，所以直接断掉所有连接。

case BluetoothHeadset.STATE_CONNECTED:

if (DBG) log(”Already connected to ” + mHeadsetAddress + “,disconnecting” +info.mAddress);

mBluetooth.disconnectRemoteDeviceAcl(info.mAddress);

break;

蓝牙耳机也可能会主动发起SCO 连接， BluetoothHandsfree 会接收到一个SCO_ACCEPTED消息，它会去调用AudioManager 的setBluetoothScoOn 函数，从而通知音频系统有个蓝牙耳机可用了。到此，蓝牙耳机完成了和Android 的全部连接。

case SCO_ACCEPTED:

if (msg.arg1 == ScoSocket.STATE_CONNECTED) {

if (isHeadsetConnected() && mAudioPossible && mConnectedSco ==null) {

Log.i(TAG, “Routing audio for incoming SCO connection”);

mConnectedSco = (ScoSocket)msg.obj;

mAudioManager.setBluetoothScoOn(true);

} else {

Log.i(TAG, “Rejecting incoming SCO connection”);

((ScoSocket)msg.obj).close();

}

} // else error trying to accept, try again

mIncomingSco = createScoSocket();

mIncomingSco.accept();

break;
分享到：