Android provides a default Bluetooth stack that supports both Classic Bluetooth and Bluetooth Low Energy. Using Bluetooth, Android devices can create personal area networks to send and receive data with nearby Bluetooth devices.
In Android 4.3 and later, the Android Bluetooth stack provides the ability to implement Bluetooth Low Energy (BLE). To fully leverage the BLE APIs, follow the Android Bluetooth HCI Requirements. Android devices with a qualified chipset can implement either Classic Bluetooth or both Classic Bluetooth and BLE. BLE is not backwards compatible with older Bluetooth chipsets.
In Android 8.0, the native Bluetooth stack is fully qualified for Bluetooth 5. To use available Bluetooth 5 features, the device needs to have a Bluetooth 5 qualified chipset.
Android architecture
A Bluetooth app communicates with the Bluetooth process through Binder. The Bluetooth process uses JNI to communicate with the Bluetooth stack and provides developers with access to various Bluetooth profiles. This diagram shows the general structure of the Bluetooth stack:
- App framework
- At the app framework level is app code, which uses the android.bluetooth APIs to interact with the Bluetooth hardware. Internally, this code calls the Bluetooth process through the Binder IPC mechanism.
- Bluetooth app
-
The Bluetooth app, located in
packages/modules/Bluetooth/android/app, is packaged as an Android app and implements the Bluetooth profiles at the Android framework layer. This app calls into the native Bluetooth stack through JNI. - JNI
-
The JNI code associated with android.bluetooth is located in
packages/modules/Bluetooth/android/app/jni. The JNI code calls into the Bluetooth stack when certain Bluetooth operations occur, such as when devices are discovered. - Bluetooth stack
-
The default Bluetooth stack is provided in AOSP and is located in
packages/modules/Bluetooth/system. The stack implements the generic Bluetooth HAL and customizes it with extensions and configuration changes. - Vendor implementation
- Vendor devices interact with the Bluetooth stack using the Hardware Interface Design Language (HIDL).
HIDL
HIDL defines the interface between the
Bluetooth stack and the vendor implementation. To generate the Bluetooth HIDL files, pass the
Bluetooth interface files into the HIDL generation tool. The interface files are located in
hardware/interfaces/bluetooth.
Bluetooth stack development
The Android Bluetooth stack is a fully qualified Bluetooth stack. The qualification listing is on the Bluetooth SIG website under QDID 169365.
The core Bluetooth stack resides in
packages/modules/Bluetooth. Development happens in AOSP, and contributions are welcome.
Android 7.x and lower architecture
A Bluetooth system service communicates with the Bluetooth stack through JNI and with apps through Binder IPC. The system service provides developers with access to various Bluetooth profiles. This diagram shows the general structure of the Bluetooth stack:
- App framework
-
At the app framework level is app code, which uses the
android.bluetoothAPIs to interact with the Bluetooth hardware. Internally, this code calls the Bluetooth process through the Binder IPC mechanism. - Bluetooth system service
-
The Bluetooth system service, located in
packages/apps/Bluetooth, is packaged as an Android app and implements the Bluetooth service and profiles at the Android framework layer. This app calls into the HAL layer through JNI. - JNI
-
The JNI code associated with
android.bluetooth
is located in
packages/apps/Bluetooth/jni. The JNI code calls into the HAL layer and receives callbacks from the HAL when certain Bluetooth operations occur, such as when devices are discovered. - HAL
-
The hardware abstraction layer defines the standard interface that the
android.bluetooth
APIs and Bluetooth process call into and that you must implement to have your Bluetooth
hardware function correctly. The header file for the Bluetooth HAL is
hardware/libhardware/include/hardware/bluetooth.h. Additionally, review all of thehardware/libhardware/include/hardware/bt_*.hfiles. - Bluetooth stack
-
The default Bluetooth stack is provided for you and is located in
system/bt. The stack implements the generic Bluetooth HAL and customizes it with extensions and configuration changes. - Vendor extensions
- To add custom extensions and an HCI layer for tracing, you can create a libbt-vendor module and specify these components.
Implement the HAL
The Bluetooth HAL is located in
/hardware/libhardware/include/hardware/bluetooth.h. The
bluetooth.h file contains the basic interface for the Bluetooth stack, and you
must implement its functions.
Profile-specific files are located in the same directory. For details, see the HAL File Reference.