Sensors, Actuators and Attributes

Sensors are signals to read values of properties in a vehicle. Values of sensors typically change over time. Reading a sensor shall return the current actual value of the related property, e.g. the current speed or the current position of the seat.

Actuators are used to control the desired value of a property. Some properties in a vehicle cannot change instantly. A typical example is position of a seat or a window. Reading a value of an actuator shall return the current actual value, e.g. the current position of the seat, rather than the wanted/desired position. A typical example could be if someone wants to change the position of a seat from 0 to 100. This can be changed by setting the corresponding actuator to 100. If the actuator is read directly after the set request it will still return 0 as it might take some seconds before the seat reaches the wanted position of 100. If the seat by some reason is blocked or cannot be moved due to safety reasons it might never reach the wanted position. It is up to the vehicle to decide how long time it shall try to reach the desired value and what to do if it needs to give up.

Attributes are signals that have a default value, specified by its default member. The standard Vehicle Signal Specification does not include default values for all attributes. If a default value has not been specified then the OEM must define a default value matching the actual vehicle. If the standard defines a default value but it does not fit the actual vehicle, then the OEM must override the standard default value.

Attribute values can also change, similar to sensor values. The latter can be useful for attribute values that are likely to change during the lifetime of the vehicle. However, attribute values should typically not change more than once per ignition cycle, or else it should be defined as a sensor instead.

A data entry for a signal defines its members. A data entry example is given below:

Vehicle.Speed:
  type: sensor
  datatype: float
  unit: km/h
  description: Vehicle speed.

Each data entry has a name, in the example above Vehicle.Speed. VSS use a dot-notated name style where the full path of a data entry consists of all parent branches from the root node separated by dots and at the end the name of the data entry itself. In the standard VSS catalog the root node is called Vehicle.

When using *.vspec files to define a VSS catalog it is not necessary to give the full dot-notated name for each data-entry, as the *.vspec format supports includes that can be used to append entries to a specific branch.

In addition to sensor, actuatorand attribute VSS also support entries to describe struct data types. The information on data entry attributes below is partially valid also for structs.

Mandatory Data Entry Attributes

This is the list of attributes that must be specified for every data entry.

Optional Data Entry Attributes

In additon to the mandatory attributes some optional attributes have been defined. There may be additional constraints on their usage not specified in the table below.