Talk to Your Toaster:
Bluetooth In Your Applica6on Dave Smith @devunwired Get the Examples: h.p://github.com/devunwired/accessory-samples 

About the Author 

Bluetooth “Classic” Basics 3 • Device Discovery – Search field of range for discoverable devices – Discoverable devices can be queried for name, class, list of services • Pairing/Bonding – Before a connec6on can be established – As of Bluetooth 2.1, authen6ca6on is op6onal using Secure Simple Pairing (SSP) – Pairing is the process that leads to a two devices being bonded • Protocols and Profiles – Devices implement profiles, built on top of protocols, to provide services to clients – Logical Link Control and Adapta6on Protocol (L2CAP) • Advanced Audio Distribu6on Profile (A2DP) • Human Interface Device (HID) – Radio Frequency Communica6ons (RFCOMM) • Serial Port Profile (SPP) – Service Discovery Protocol (SDP) • Client/Server Model – Servers "have" data, clients "access" data. Mobile device typically the client. 

Bluetooth Services • Each device publishes one or more services available to connect with • Iden6fied by a UUID – Standard services are 16-bit added to a common 128-bit base: • 00000000-0000-1000-8000-00805F9B34FB – Custom services can be any generated UUID • Common Service UUIDs – RFCOMM: 0x0003 – L2CAP: 0x0100 – Serial Port (SPP): 0x1101 – A2DP AudioSource: 0x110A – A2DP AudioSink: 0x110B • Full SPP UUID = 00001101-0000-1000-8000-00805F9B34FB 4 

A Well-Known UUID... 5 

Bluetooth LE 6 • Bluetooth 4.0 (Bluetooth Smart) – Uses the General Aeributes (GATT) profile, built on the Aeributes (ATT) protocol – S6ll runs on top of L2CAP protocol • Server (accessory) devices adver6se presence – Contrast with listeners in BT Classic • Client devices scan for adver6sement packets • Device Roles – Central (client) – Peripheral (server) – Broadcaster (server) – Observer (client) • Central and Observer roles only in the current APIs 

GATT Profile Service <16-bit AssignedNumber> Service GATT Peripheral 7 Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value Characteris6c Proper6es Value 

Visualizing the Stack 8 RF Radio Link Layer L2CAP Protocol RFCOMM Protocol Serial Port Profile RF Radio Link Layer L2CAP Protocol Attribute Protocol GATT Profile Bluetooth 2.1 BR/EDR Bluetooth 4.0 LE • Bluetooth Classic – Single mode – No BLE support • Bluetooth Smart – Single mode – BLE only • Bluetooth Smart Ready – Dual mode 

Bluetooth APIs 9 2.0 2.3.3 3.0 RFCOMM Support Insecure RFCOMM (SSP) Classic Profile Support A2DP HFP HDP 

BluetoothDevice BluetoothAdapter getBondedDevices() getRemoteDevice(ADDRESS) Async Scan Broadcast ACTION_FOUND Broadcast ACTION_DISCOVERY_FINISHED startDiscovery() cancelDiscovery() Discovering Classic Devices 10 BluetoothDevice BluetoothAdapter 

Service UUID Discovery (Op6onal) Class cl = Class.forName("android.bluetooth.BluetoothDevice");
 Class[] par = {};
 Method method = cl.getMethod("getUuids", par);
 Object[] args = {};
 ParcelUuid[] retval = (ParcelUuid[]) method.invoke(device, args);
 String uuid = retval[0].toString(); • Public APIs to discover service UUIDs added in 4.0.3 (API 15) • For earlier versions BluetoothDevice Async Scan ParcelUuid fetchUuidsWithSdp() getUuids() Broadcast ACTION_UUID 

RFCOMM Connec6ons 12 BluetoothAdapter BluetoothDevice BluetoothSocket BluetoothServerSocket createRfcommSocketToServiceRecord(UUID) createInsecureRfcommSocketToServiceRecord(UUID) accept() BluetoothSocket connect() listenUsingRfcommWithServiceRecord(UUID) listenUsingInsecureRfcommWithServiceRecord(UUID) getOutputStream() getInputStream() 

GATT Discovery 13 BluetoothDevice BluetoothAdapter BluetoothGatt Async Scan startLeScan(ScanCallback) stopLeScan() ScanCallback.onLeScan() connectGatt(GattCallback) BluetoothGattCallback BluetoothGatt BluetoothGattService BluetoothGattCharacteristic BluetoothGattDescriptor discoverServices() onServicesDiscovered() getServices() getService(UUID) getCharacteristics() getCharacteristic(UUID) getDescriptors() getDescriptor(UUID) 

GATT Transac6ons 14 BluetoothGattCallback BluetoothGattCharacteristic BluetoothGattDescriptor BluetoothGatt readCharacteristic() writeCharacteristic() readDescriptor() writeDescriptor() setCharacteristicNotification() onCharacteristicRead() onCharacteristicWrite() onCharacteristicChanged() onDescriptorRead() onDescriptorWrite() 

LE Tips • Wait for read/write callbacks – Don't queue up mul6ple commands • Post your results – Callbacks aren't on the main thread • No6fica6ons have to be set local and remote – setCharacteris6cNo6fica6on() for local – writeCharacteris6c() for remote • Max 4 simultaneous ac6ve no6fica6ons • Ensure device has LE support – in AndroidManifest.xml • "android.hardware.bluetooth_le" – PackageManager.hasSystemFeature() 15 

LE Broadcasters • Non-connectable adver6sing devices • Also known as beacons • Provides all service data in the adver6sement – Adver6sement Data (AD) Structure – Packet contains collec6on of AD Structures • onLeScan() provides AD collec6on from raw scan record. • Faster access to data – No connec6on overhead • Simpler accessory stack implementa6on 16 

Adver6sement Data 17 AD Length AD Type AD Payload AD Structure AD Structure AD Structure ... AD Structure AD Structure AD Structure AD Structure ... AD Structure public void onLeScan(BluetoothDevice, int rssi, byte[] scanRecord) Type Iden6fiers are Assigned Numbers by the Bluetooth SIG Device Name, Service UUIDs, Service Data, TX Power, etc. heps://www.bluetooth.org/en-us/specifica6on/assigned-numbers/generic-access-profile 

Profile Connec6ons • Android 3.0+ supports connec6ng to certain Bluetooth device classes • BluetoothProfile – Common interface for all supported device profiles – Reports connec6on status of any devices matching the profile – Profile-specific ac6ons implemented in subclasses • Use BluetoothAdapter.getProfileProxy() to register a ServiceListener callback for connec6on events – Binder Proxy to control device's Bluetooth Service • ServiceListener is passed an instance of the profile when a device matching it is connected. 18 

Headset Example BluetoothHeadset mBluetoothHeadset;
 BluetoothDevice mDevice;
 // Get the default adapter
 BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
 
 private BluetoothProfile.ServiceListener mProfileListener =
 new BluetoothProfile.ServiceListener() {
 public void onServiceConnected(int profile, BluetoothProfile proxy) {
 if (profile == BluetoothProfile.HEADSET) {
 mBluetoothHeadset = (BluetoothHeadset) proxy;
 }
 }
 
 public void onServiceDisconnected(int profile) {
 if (profile == BluetoothProfile.HEADSET) {
 mBluetoothHeadset = null;
 }
 }
 }; // Establish connection to the proxy.
 mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.HEADSET);
 
 mDevice = mBluetoothHeadset.getConnectedDevices().get(0);
 mBluetoothHeadset.startVoiceRecognition(mDevice);
 
 // Close proxy connection
 mBluetoothHeadset.stopVoiceRecognition(mDevice);
 mBluetoothAdapter.closeProfileProxy(BluetoothProfile.HEADSET, mBluetoothHeadset); 19 

Demos 20 

Come Find Me! 21 • Dave Smith • Twieer/App.Net: @devunwired • Google+: hep://plus.google.com/+DaveSmithDev • Blog: hep://wiresareobsolete.com • Our Work: hep://www.doubleencore.com • Beacon Hardware – hep://www.kstechnologies.com/ • Samples – hep://www.github.com/devunwired/accessory-samples