HAL (Hardware Abstraction Layer)
Bridging software and hardware
What is HAL?
The Hardware Abstraction Layer (HAL) in Android provides a standard interface for hardware vendors to implement, allowing Android OS to communicate with device hardware without knowing the hardware specifics. HAL modules act as a bridge between the Android system and hardware drivers.
Role in Android
- Enables Android to support a wide range of hardware with minimal changes to the OS.
- Vendors implement HAL modules for their hardware, which the Android system calls via defined interfaces.
- Ensures modularity and easier updates for both hardware and software.
Architecture
HAL sits between the Android Framework and the Linux kernel drivers. The typical stack is:
Android App
Android Framework
JNI (Java Native Interface)
HAL
Linux Kernel Driver
Hardware
Key Components of HAL
HIDL / AIDL
Interface Definition Languages used for inter-process communication.
Audio HAL
Connects AudioFlinger to audio hardware.
Camera HAL
Connects CameraService to camera sensors.
Sensors HAL
Provides data from accelerometer, gyro, etc.
Graphics (Gralloc)
Allocates graphics memory buffers.
Bluetooth
Manages Bluetooth radio communication.
How HAL Works
- HAL implementations are packaged as shared libraries (.so files).
- The Android system loads the correct HAL library at runtime.
- This architecture allows updating the framework without changing the lower-level drivers.
- Project Treble separated the vendor implementation from the system framework to make updates easier.