Android Automotive OS is powering a growing number of infotainment systems, and at the heart of its vehicle interaction lies a critical component: VHAL Interfaces (IVehicle). These interfaces are what allow Android to talk to your car’s hardware. From reading the speedometer to turning on climate control, everything hinges on this system.

In this post, we’ll break down how VHAL Interfaces (IVehicle) work, why they’re essential, and how developers can work with them to build automotive apps that actually connect with vehicle systems.

What Is VHAL?

VHAL stands for Vehicle Hardware Abstraction Layer. Think of it as a translator between Android and the car’s underlying ECUs (Electronic Control Units). Cars have multiple ECUs controlling everything from brakes to lights, and Android Automotive needs a way to communicate with them.

That’s where VHAL Interfaces (IVehicle) come in. They define how Android gets and sets data to and from the vehicle hardware.

The Role of IVehicle Interface

In Android Automotive, IVehicle is the AIDL (Android Interface Definition Language) interface that enables communication between the Vehicle HAL and the framework.

You can think of IVehicle as a contract. It defines methods the Android system can call to:

• Get vehicle property values (e.g., speed, fuel level)
• Set values (e.g., adjust HVAC settings)
• Subscribe to updates

This interface must be implemented by car manufacturers or Tier-1 suppliers so that Android can access real-time vehicle data.

Anatomy of IVehicle Interface

Here’s a simplified look at what an IVehicle interface might look like:

interface IVehicle {
    VehiclePropValue get(in VehiclePropGetRequest request);
    StatusCode set(in VehiclePropValue value);
    void subscribe(in IVehicleCallback callback, in SubscribeOptions[] options);
    void unsubscribe(in IVehicleCallback callback, in int[] propIds);
}

Here,

• get(): Used to read a vehicle property.
• set(): Used to write or modify a property (like setting temperature).
• subscribe(): Listen for changes (like speed updates).
• unsubscribe(): Stop listening to property changes.

These methods form the foundation of vehicle interaction in Android Automotive.

What Is a Vehicle Property?

A vehicle property is any data point Android can interact with. Each has a unique ID, data type, and permission level. For example:

• VehicleProperty::PERF_VEHICLE_SPEED: Car speed
• VehicleProperty::HVAC_TEMPERATURE_SET: Climate control temperature
• VehicleProperty::FUEL_LEVEL: Fuel level

Each property is defined in the VehicleProperty.aidl file.

Implementing a Custom VHAL

Let’s say you’re a car maker. You want Android to read your custom battery voltage data. You’d do something like this:

1. Define the Property

#define VEHICLE_PROPERTY_CUSTOM_BATTERY_VOLTAGE (0x12345678)

2. Add It to Your Property List

VehiclePropConfig config = {
    .prop = VEHICLE_PROPERTY_CUSTOM_BATTERY_VOLTAGE,
    .access = VehiclePropertyAccess::READ,
    .changeMode = VehiclePropertyChangeMode::ON_CHANGE,
    .configArray = {},
    .configString = "Custom Battery Voltage",
};

3. Implement Logic in get()

VehiclePropValue get(const VehiclePropGetRequest& request) override {
    VehiclePropValue value = {};
    if (request.prop == VEHICLE_PROPERTY_CUSTOM_BATTERY_VOLTAGE) {
        value.prop = request.prop;
        value.value.floatValues = {12.6};
    }
    return value;
}

And that’s it. Now Android can read your custom battery voltage.

Why Are VHAL Interfaces (IVehicle) Important?

Without VHAL, Android is blind to the vehicle. These interfaces power key services like:

• HVAC control UI
• Instrument cluster apps
• Battery status for EVs
• Safety features

By standardizing communication, VHAL Interfaces (IVehicle) make it possible for third-party developers to build real, vehicle-aware apps. That’s a game-changer.

Example: Reading Vehicle Speed

Let’s look at a code snippet that reads the vehicle speed.

Requesting Speed in Framework (Java)

VehiclePropertyValue speed = vehicle.get(VehicleProperty.PERF_VEHICLE_SPEED);
float currentSpeed = speed.getValue().getFloatValue();

Here,

• The Java API calls the get() method on the IVehicle AIDL interface.
• This request travels through the HAL to the car’s CAN bus or hardware.
• The current speed is returned as a float.

Best Practices for Working with VHAL

1. Don’t poll: Use subscribe() instead of calling get() in a loop.
2. Permission-aware: Some properties require special permissions.
3. Optimize data flow: Avoid flooding the system with updates.
4. Test on real hardware: Simulators are helpful, but actual ECUs may behave differently.

Conclusion

If you want to build or integrate automotive systems with Android Automotive OS, you must understand how VHAL Interfaces (IVehicle) work. They’re the core pathway between Android and the car’s brain.

With the right implementation, you can create apps that do more than just run in the dashboard — they interact with the vehicle in real-time, improving safety, convenience, and experience.

VHAL Interfaces (IVehicle) are not just another Android abstraction. They’re what make Android truly automotive.