What’s all that hype about BLE?

Software Engineer

relayr

Hugo Doménech Juárez@hudomju

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relayrbring things to life

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Why are startups shifting to hardware products?

- Sensors are cheap!8

Prototyping tools

-3d Printer

-CNC Machine

-Laser Cutter

-3d Scanner

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What do all these products have in

common?

-The way they communicate!13

Bluetooth Low Energy

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Bluetooth Classic

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Relationship between Bluetooth and Android

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Eclair 2.0 (API 5)BlueZ

Android 1.x

4.3 (API 18)

Bluedroid

JellyBean

Bluetooth Smart 5.0 (API 20)

Lollipop

Full BLE

Older Broadcom stack - Samsung & HTC < 4.0Motorola Bluetooth Stack

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Bluetooth Low Energy

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Central Peripheral

Observer Broadcaster

Android 4.3+ Android 5.0+

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BLE Scanning example

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BLE Scanning

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BLE Scanning

<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="false"/>

boolean hasBleFeature() { return getPackageManager().hasSystemFeature(FEATURE_BLUETOOTH_LE)); }

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BLE Scanning

mBluetoothAdapter.startLeScan(mLeScanCallback);

mBluetoothAdapter.stopLeScan(mLeScanCallback);

BluetoothManager manager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE); mBluetoothAdapter = bluetoothManager.getAdapter();

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BLE Scanning

private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() {

@Override public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) { // You are not in the UI thread

// or in the thread you subscribed for what matters! } };

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BLE Scanning

/** * Decodes the services uuid from the advertisement packet since * {@link android.bluetooth.BluetoothDevice#getUuids()} returns null most of * the times. */ public static List<String> decodeServicesUuid(byte[] data);

/** * Decodes the device name from the Complete Local Name or Shortened * Local Name field in the * Advertisement packet. {@link * android.bluetooth.BluetoothDevice#getName()} does it already, * although some phones skip it. i.e. Sony Xperia Z1 (C6903) with Android 4.3 * where getName() always returns <code>null</code>. */ public static String decodeDeviceName(byte[] data);

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BLE Scanning: Lollipop improvements

mBluetoothAdapter.startScan(filters, scanSettings, scanCallback)

namedeviceAddress

uuid

serviceDataUuid

serviceData

manufacturerId

manufacturerData

Low Power

Balanced

Low Latency

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interface ScanCallback {

public void onScanResult(int callbackType, ScanResult result);

public void onBatchScanResults(List<ScanResult> results);

public void onScanFailed(int errorCode)

}

BLE Scanning: Lollipop improvements

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Advertisement

GATT server

Hardware feature

- chipset needs to support it - nexus 9 vs nexus 5 & 7

BluetoothAdapter.isMultipleAdvertisementSupported()

Peripheral mode: Lollipop features

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Let’s connect to other BLE devices!

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The GATT Protocol

Peripheral Central

Read - Write - Subscribe

Respond - Push

GATT Peripheral GATT protocol

Service

Service

Characteristic

Characteristic

Value

Indications Notifications

Descriptor

Descriptor Descriptor

31Server Client

Generic Attribute Profile

The GATT Protocol

class BluetoothAdapterLeScanCallback {

void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) {

device.connectGatt(context, false, mBluetoothGattReceiver);

}

}

class BluetoothGattReceiver { @Override public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {} }

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The BluetoothGatt

discoverServices

writeCharacteristic

readCharacteristic

writeDescriptor

setCharacteristicNotification

readDescriptor

readRemoteRssi

beginReliableWrite

executeReliableWrite

abortReliableWrite

readMtu

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The BluetoothGattCallback

onServicesDiscovered

onCharacteristicWrite

onCharacteristicRead

onDescriptorWrite

onCharacteristicChanged

onDescriptorRead

onRemoteRssiRead

onReliableWriteCompleted

onMtuChanged

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Why would you write characteristics?

A practical example

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Data subscriptions: Indication / Notification

gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(ENABLE_NOTIFICATION_VALUE); gatt.writeDescriptor(descriptor);

gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(ENABLE_INDICATION_VALUE); gatt.writeDescriptor(descriptor);

gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(DISABLE_NOTIFICATION_VALUE); gatt.writeDescriptor(descriptor);

@Override public void onCharacteristicChanged( BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) { }

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Reliable Write ?= Long Write

gatt.beginReliableWrite(); characteristic.setValue(data); gatt.reliableWriteCharacteristic(mBluetoothGatt, characteristic, subscriber); gatt.executeReliableWrite();

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18 byte: 16 bytes content + 1 offset + 1 length package

Regular Write supports 18 bytes

Disconnecting GATT vs Closing GATT

gatt.disconnect();

@Override public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {

if (newState == STATE_DISCONNECTED && noLongerInterestedInTheDevice) {

gatt.close();

} }

gatt.close();

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Stack metrics: why you should close your GATT

- Constants defined in BlueDroid - Max concurrent active notifications

- BTA_GATTC_NOTIF_REG_MAX - (4) Android 4.3 - (7) Android 4.4 - (15) Android 5.0+

- Max concurrent GATT connections - BTA_GATTC_CON_MAX - (4) Android 4.3 - (7) Android 4.4+

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… and one last thing

Security

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Security

Pairing

Bonding

Encryption Re-establishment

- Just Works - Passkey Entry - Out Of Band

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Security: Instability

static class UndocumentedBleStuff {

static boolean isUndocumentedErrorStatus(int status) { return status == 133 || status == 137; }

static void fixUndocumentedBleStatusProblem(BluetoothGatt gatt, BluetoothGattReceiver receiver) {

DeviceCompatibilityUtils.refresh(gatt); gatt.getDevice().connectGatt(RelayrApp.get(), false, receiver); } }

GATT_INSUFFICIENT_AUTHENTICATION GATT_INSUFFICIENT_ENCRYPTION

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Security: Instability

boolean refresh(BluetoothGatt gatt) { try { Method localMethod = gatt.getClass().getMethod("refresh", new Class[0]); if (localMethod != null) { return (Boolean) localMethod.invoke(gatt); } } catch (Exception localException) { Log.e(TAG, "An exception occurred while performing: refresh”, localException.getCause()); } return false; }

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Security: Instability

class DeviceCompatibilityUtils {

boolean createBond(BluetoothDevice device) { if (isSdk19()) return doCreateBond(device); return callMethod(device, "createBond"); }

@TargetApi(Build.VERSION_CODES.KITKAT) boolean doCreateBond(BluetoothDevice device) { return device.createBond(); }

boolean removeBond(BluetoothDevice device) { return callMethod(device, "removeBond"); } }

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So we can develop now for Android Wearables right?

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Bluetooth SIG (Special Interest Group)

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Questions?Hugo Doménech

@hudomju

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