Vehicle Functions

Last edit: 2023.07.27

The vehicle functions domain APIs and modules enable TomTom Digital Cockpit to interact with the vehicle, like opening a window, setting the Air Conditioning temperature, or being informed about the current speed.


A TomTom Digital Cockpit-based system consists of multiple parts: the vehicle platform, Android services, and TomTom Digital Cockpit. The vehicle platform is the part that Android Car uses to communicate with the vehicle.

Because vehicle platforms differ from brand to brand, and sometimes even from model to model, TomTom Digital Cockpit provides an abstraction of that vehicle platform. By adding an IviService layer on top of Android Car, TomTom Digital Cockpit can communicate with each vehicle using the same interface.

This interface uses its own definitions of the properties a vehicle platform may expose and enables property observers to obtain the values of these properties, as well as a means of changing their value.

Vehicle functions decomposition

As shown in the diagram, TomTom Digital Cockpit has a single interface for all types of vehicle platforms. In the platform_vehiclefunctions_api_common_vehiclefunctions module we define the different types of vehicle properties and how we communicate with them.

The vehicle function services are built on top of Android Car, which in turn uses the Vehicle Hardware Abstraction Layer (VHAL). Working our way up we describe how to write or use a vehicle function service.

All communication is asynchronous. This means that you can make vehicle property change requests and the current thread will not be blocked. Any effects of your request will come in the shape of vehicle property value changes, or in the shape of an error callback. In the background, the vehicle platform decides what should happen, changes the vehicle's state, and updates the vehicle's properties, sending any changed values back to TomTom Digital Cockpit.

Android VHAL interface

The Android VHAL abstracts away the vehicle properties. This interface is best described in Android's VHAL overview and the Android's HAL definition. In summary it offers the following:

  • A method to list all configurations of properties supported by the VHAL. A single configuration describes:
    • access mode (read, write, read/write),
    • change mode (static, on change, continuous),
    • value type, and
    • min/max sample rate.
  • A method to set a property value per zone, with an error return value if the vehicle system owning the property has not been properly initialized yet.
  • A method to get a property value per zone, with an error return value if there is no data available.
  • A method to subscribe to property changes per zone. Subscription type can be on change or continuous with a given update frequency or sample rate.
  • An error callback method.

Android Car interface

The Android Car interface relies on the CarPropertyManager. It uses the VHAL interface definition to create an implementation. In summary it offers the following:

  • A type-safe and zone-dependent getProperty method.
  • A type-safe and zone-dependent setProperty method.
  • A method to check a property availability.
  • A method to get a property configuration:
    • access mode,
    • change mode,
    • min/max sample rate,
    • min/max value,
    • value type,
    • supported zones.
  • A method to get the configuration of all properties.
  • A method to subscribe to changes at a certain rate: 1Hz, 5Hz, 10Hz, 100Hz, on change.
  • An error callback method triggered for errors when setting a property fails: access denied, invalid arg, property not available, try again, unknown.
  • Methods may take multiple seconds to complete.
  • Exceptions are thrown in case of errors.

TomTom Digital Cockpit interface

The following list of restrictions drove the design of the TomTom Digital Cockpit Vehicle Functions:

  • A vehicle function service supports an API to discover vehicle capabilities.
  • A vehicle function service exposes error states provided by the VHAL.
  • A vehicle function service API does not depend on Android Car.
  • The state exposed by the interfaces of the vehicle application services and vehicle function services is always initialized and set to unavailable if not all dependent layers are yet initialized.
  • The VHAL validates data conformity of the exposed properties. An error is reported in the case of non-conformity.

Vehicle properties

Vehicle properties are always in one of three states:

  • unsupported, when a property is not supported by the vehicle platform.
  • supported, when a property is supported by the vehicle platform.
  • available, when a property is supported and has a valid value.

Instead of using state flags, the vehicle function service APIs use nullable parameters:

  • The property is null when the vehicle property is unsupported.
  • The value of the property is null when the property is (temporarily) not available.


1when {
2 property == null -> unsupported()
3 property.value == null -> supportedButNotAvailable()
4 else -> supportedAndAvailable()

Or, when the supported state is not relevant:

1when (property?.value) {
2 null -> unsupportedOrNotAvailable()
3 else -> supportedAndAvailable()

Implementing a vehicle functions service

A vehicle functions service interface should have the @IviService annotation so TomTom Digital Cockpit can discover it:

1\@IviService ( serviceId = "com.tomtom.ivi.service.example" )
2interface VehicleExampleService {
3 // ...

Readable properties

The interface should provide a readable and observable value of any readable vehicle property. The vehicle functions service ensures that the value is within a specified range.

val [propertyName]: [type]Property?
val [zonePropertyName]: [type]ZoneProperty?

Writable properties

The interface should provide a setter function for any writable properties. It should return false if the property could not be updated, for example when the property is not (yet) available. The @IviServiceFun annotation and suspend are required to expose the service function to the generated API version of this service.

Note: These are only possible for vehicle properties with write access.

suspend fun set[PropertyName](value: [type]): Boolean

Zoned writable properties

The interface should provide a setter function for any writable properties which work in a certain area. It should return false if the property could not be updated, for example when the property is not (yet) available. The @IviServiceFun annotation and suspend are required to expose the service function to the generated API version of this service.

Note: These are only possible for vehicle properties with write access.

2suspend fun set[PropertyName](area: PropertyArea, value: [type]): Boolean

See also Areas.

Property Availability

The availability of a property is decided based on various factors:

  • If the underlying layers are not ready yet, the property is unavailable.
  • If an error occurs while reading the property, the property may become (temporarily) unavailable.
  • Certain business rules may cause the property to become (temporarily) unavailable, like legal restrictions or country restrictions.

Property Areas

Some vehicle properties may have zoned values within a certain area, like the driver seat zone for the seat heating property in the SEAT area, or the passenger side window zone in the WINDOW area. An area describes which part of a vehicle a property belongs to, while the zone signifies which part, or parts, of that area a value is about.

Take the cabin temperature for example. Let's assume that the vehicle allows the temperature on two sides of the vehicle, left and right, to be set separately. Because the cabin temperature concerns the location where people are sitting, the SEAT area should be used. The VHAL supports three rows of three seats, so the rows need to be split unevenly into two zones: left/center and right. By setting the cabin temperature for the left/center zone in the SEAT area separately, the right zone temperature is unaffected, and vice versa.

If there is no specific area applicable to the property, then the VehicleProperties.ListProperty (or any other Property type) is used. If the area is relevant, then the VehicleZoneProperty type is used, providing a value per area.

An area must be a sub-type of WINDOW, SEAT, DOOR, MIRROR, or WHEEL. It must also include a zone, like: WINDOW_ROW_1_LEFT or SEAT_ROW_2_CENTER. See the com.tomtom.ivi.platform.vehiclefunctions.api.common.vehiclefunctions package documentation for more examples.

The platform_vehiclefunctions_api_service_vehicleelectricengine module shows the definition of a simple vehicle functions service. It only exposes the current battery level for an Electric Vehicle (EV) or a hybrid vehicle. See the example application to see how this gets used.

The platform_vehiclefunctions_api_service_vehiclehvac module is a definition of an IVI service that is a conduit to the HVAC functionalities of the vehicle. It shows how to define a more involved interface for your service.