EVERYTHING ABOUT BLUETOOTHJohnny Sung

02. Peripheral mode in Android

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Johnny SungMobile devices Developer

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(Samsung S6 Edge)Peripheral Central

(LG Nexus 5)

2.0 2.0 + 4.0 Dual Mode 4.0Bluetooth SMART READYBluetooth Bluetooth SMART

Bluetooth low energy Protocol Stack

• Peripheral

• Central

• Broadcaster

• Observer

GAP Roles

PeripheralCentral

PeripheralCentral

PeripheralCentral

GATT

• Service

• Characteristic

• Data

• Descriptor

GATT

• Heart Rate Service

• Heart Rate Measurement

• Data

• Descriptor

00002A37-0000-1000-8000-00805F9B34FB

GATT

Heart Rate Monitor

0000180D-0000-1000-8000-00805F9B34FB

Property: Notify

Property: Indicate

• Health Thermometer

• Temperature Measurement

• Data

• Descriptor

GATT

Health Thermometer

00001809-0000-1000-8000-00805F9B34FB

00002A1C-0000-1000-8000-00805F9B34FB

• Read

• Write

• Notify

• Indicate

Characteristic Properties

UUID

00002A37-0000-1000-8000-00805F9B34FB

0x2A37Heart Rate Measurement

• an indicate operation is identical to a notify operation except that indications are acknowledged, while notifications are not.

Notify vs Indicate

http://mbientlab.com/blog/bluetooth-low-energy-introduction/

https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.health_thermometer.xml

Property: Indicate

• Health Thermometer

• Temperature Measurement

• Data

• Descriptor

GATT

Health Thermometer

00001809-0000-1000-8000-00805F9B34FB

00002A1C-0000-1000-8000-00805F9B34FB

• Central

• Android 4.3 (API Level 18)

• Peripheral

• Android 5.0 (API Level 21)

• Specific BLE chip

Requirement in Android

What? Specific BLE chip ?

http://altbeacon.github.io/android-beacon-library/beacon-transmitter-devices.html

BluetoothManager manager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE); BluetoothAdapter adapter = manager.getAdapter();

adapter.isMultipleAdvertisementSupported();

Check if devices support Peripheral mode

PERIPHERAL

<uses-permission android:name="android.permission.BLUETOOTH"/><uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/><uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

Bluetooth permissions

AndroidManifest.xml

Bluetooth permissionsCheck system featuregetPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)

@Overridepublic void onActivityResult(int requestCode , int resultCode, Intent data) { if (requestCode == REQUEST_ENABLE_BT) { if (resultCode == Activity.RESULT_OK) { // Bluetooth has turned on } else { // User did not enable Bluetooth or an error occurred } }}

Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); startActivityForResult(enableIntent, REQUEST_ENABLE_BT);

Request to enable Bluetooth

BluetoothGattService hrmService = new BluetoothGattService(SERVICE_HEALTH_THERMOMETER_UUID, BluetoothGattService.SERVICE_TYPE_PRIMARY);

BluetoothGattCharacteristic tempChar = new BluetoothGattCharacteristic(CHAR_TEMP_UUID,

BluetoothGattCharacteristic.PROPERTY_INDICATE, BluetoothGattCharacteristic.PERMISSION_READ);

tempChar.addDescriptor(new BluetoothGattDescriptor( UUID.fromString("00002902-0000-1000-8000-00805f9b34fb"), (BluetoothGattDescriptor.PERMISSION_READ | BluetoothGattDescriptor.PERMISSION_WRITE))); hrmService.addCharacteristic(tempChar);

Prepare service structure

Health Thermometer

2A1C

1809

AdvertiseData.Builder datas = new AdvertiseData.Builder(); AdvertiseSettings.Builder settings = new AdvertiseSettings.Builder(); datas.addServiceUuid(new ParcelUuid(hrmService.getUuid()));

BluetoothLeAdvertiser advertiser = adapter.getBluetoothLeAdvertiser(); advertiser.startAdvertising(settings.build(), datas.build(), advertiseCallback);

BluetoothManager manager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE); BluetoothAdapter adapter = bluetoothManager.getAdapter();

BluetoothGattServer gattServer = manager.openGattServer(context, gattServerCallback);

gattServer.addService(hrmService);

Open server

Advertise to others

AdvertiseCallback advertiseCallback = new AdvertiseCallback() { @Override public void onStartSuccess(AdvertiseSettings settingsInEffect) { // ... } @Override public void onStartFailure(int errorCode) { // ... } };

Advertise callback

private HashSet<BluetoothDevice> bleDevices = new HashSet<>(); private final BluetoothGattServerCallback gattServerCallback = new BluetoothGattServerCallback() { @Override public void onConnectionStateChange(BluetoothDevice device, int status, int newState) { super.onConnectionStateChange(device, status, newState); if (status == BluetoothGatt.GATT_SUCCESS) { if (newState == BluetoothGatt.STATE_CONNECTED) { // Connect bleDevices.add(device); } else if (newState == BluetoothGatt.STATE_DISCONNECTED) { // Disconnect bleDevices.remove(device); } } else { // Disconnect with error bleDevices.remove(device); } } // ... (略) };

Handle device connect

private final BluetoothGattServerCallback gattServerCallback = new BluetoothGattServerCallback() { // ... (略) @Override public void onCharacteristicReadRequest(BluetoothDevice device, int requestId, int offset, BluetoothGattCharacteristic characteristic) { // ... gattServer.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, offset, characteristic.getValue()); } // ... (略) };

Reading Characteristic

Writing Characteristic

http://developer.android.com/reference/android/bluetooth/BluetoothGattServerCallback.html#onCharacteristicWriteRequest(android.bluetooth.BluetoothDevice, int, android.bluetooth.BluetoothGattCharacteristic,

boolean, boolean, int, byte[])

private final BluetoothGattServerCallback gattServerCallback = new BluetoothGattServerCallback() { // ... (略) @Override public void onCharacteristicWriteRequest(BluetoothDevice device, int requestId, BluetoothGattCharacteristic characteristic, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) { // ... ByteBuffer buffer = ByteBuffer.wrap(value); buffer.order(ByteOrder.LITTLE_ENDIAN); characteristic.setValue(buffer.getInt(), BluetoothGattCharacteristic.FORMAT_UINT16, 0); if (responseNeeded) { gattServer.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, 0, null); } } // ... (略) };

private final BluetoothGattServerCallback mGattServerCallback = new BluetoothGattServerCallback() { // ... (略) @Override public void onDescriptorWriteRequest(BluetoothDevice device, int requestId, BluetoothGattDescriptor descriptor, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) { super.onDescriptorWriteRequest(device, requestId, descriptor, preparedWrite, responseNeeded, offset, value); if (responseNeeded) { gattServer.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, 0, null); } } // ... (略) };

Writing Descriptor

public void sendNotificationToDevices( BluetoothGattCharacteristic characteristic) { boolean indicate = (characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) == BluetoothGattCharacteristic.PROPERTY_INDICATE; for (BluetoothDevice device : bleDevices) { gattServer.notifyCharacteristicChanged(device, characteristic, indicate); } }

Send Characteristic Notify

Q&A

ADDITIONAL SLIDES

The story

About Nexus 5

http://altbeacon.github.io/android-beacon-library/beacon-transmitter-devices.html

https://code.google.com/p/android-developer-preview/issues/detail?id=1570

We introduced BLE peripheral mode in Android 5.0 Lollipop. Nexus 6 and Nexus 9 are the first two production Nexus devices that support BLE peripheral mode. Due to hardware chipset dependency, older Nexus devices (4/5/7) will not have access to the feature on Lollipop.

#52 Won’t Fix