SwDataDefProps - Attributes and Use Cases

Micael Coutinho,Wed Apr 03 2024 • autosar application arxml

Data definition properties can be added to data types and data prototypes, to complement their description with various attributes. They play a vital role in the meta-model, providing an enormous amount of information in each meta-class the SwDataDefProps are aggregated. Therefore, understanding each attribute, applicability for the respective meta-classes and precedence will allow you to tame this small beast and take advantage of the Autosar meta-model.

SwDataDefProps Meta-Class and its Attributes

SwDataDefProps specify the structure of elements for calibration, implementation aspects for elements, define the access policy for measurement and calibration (MCD), semantics of data elements and the code generation policy.

The attributes englobed by the SwDataDefProps meta-class are defined below:

Annotation – An aggregation of multiple annotations, enabling the addition of notes related to this meta-class.
AdditionalNativeTypeQualifier – A NativeDeclarationString used to define a set of native C qualifiers (volatile, strict, enum...) that cannot be deducted via the BaseType (typical with pointers) or from other more abstract attributes. All the qualifiers need to be provided sequentially.
BaseType – A reference to the SwBaseType associated with the data object. Commonly placed at the implementation data level to build a bridge between it and the C data type generated by the RTE.
InvalidValue – The aggregation to an optional ValueSpecification that defines the invalid value of the data object.
CompuMethod – A reference to a CompuMethod, associated with the data object semantics.
DataConstr – A reference to DataConstr applied to this element.
DisplayFormat – A DisplayFormatString that describes how the data object value should be displayed in documents and MCD tools.
DisplayPresentation – An enumeration that defines the way the object is displayed within an MCD tool. The possible values are presentationContinuous (forming a continuous plot between each point) or presentationDiscrete (a clear separation exists between each plot point).
ImplementationDataType – Reference to an AbstractImplementationDataType, used when the data object does not refer directly to a base type, which can occur the same way it does in the C programming language, for example, when the ImplementationDataType is redefined via a typedef to another ImplementationDataType, the SwPointerTarget, data type of an array or record element within an ImplementationDataType or the data type of an SwServiceArg does not refer to a base type directly.
StepSize – Defines a value that can be added or subtracted to the DataPrototype when using the plus (+) and minus (-) keys while performing calibration with an MCD tool.
SwAddrMethod – A reference that associates a SwAddrMethod to this data element. This attribute can be used to group several DataPrototypes that should be grouped together in the same memory region, without specifying the region itself at this stage of development. This and the next attribute provide valuable information for the Memory Mapping (MemMap) module in the BSW. If you need to learn more about it, check our post Memory Mapping (opens in a new tab).
SwAlignment – An AlignmentType definition, that indicates the intended alignment for the DataPrototype. If it is not specified, then the alignment is determined by the size of the swBaseType and the memoryAllocationKeywordPolicy present in the swAddrMethod. The possible values are UNKNOWN (deprecated, must not be used in new implementations), 8, 16, 32, 64, UNSPECIFIED, BOOLEAN or PTR.
SwBitRepresentation – Aggregation of a SwBitRepresentation. In case of a bit variable, it defines its binary presentation, through the attributes bitPosition (position within a bigger data object SwHostVariable) and numberOfBits (the number of bits it occupies within a bigger data object).
SwCalibrationAccess – Enumeration that defines the read and write access rights of the MCD tools to this data object. It can be notAccessible, readOnly or readWrite.
SwCalprmAxisSet – Aggregation of a SwCalprmAxisSet that specifies the axes properties, when dealing with MAPs, CURVEs, and other objects of the sort. It is mostly used for calibration parameters.
SwComparisonVariable – An aggregation of multiple SwVariableRefProxies, a set of variables used for comparison in an MCD process.
SwDataDependency – Aggregation of a single SwDataDependency, that specifies how the MCD system can calculate the value of this object through the value of another data object.
SwHostVariable – Reference to a SwVariableRefProxy that is the bigger object (the host variable) of a bit variable.
SwImplPolicy – Enumeration that describes the implementation policy of this data object. It is defined by a SwImplPolicyEnum which can take one of five possible values: const (should not be modified by the ECU and results in the const modifier in the resulting C code), fixed (the value will never change and should be implemented as a macro in C), measurementPoint (value created only for measurement purposes and should never be read directly by the software running in the ECU), queued (the data element contents should be stored as a queue and processed as a FIFO, and the RTE should implement queuing for this data object) and standard (applicable for all types of data objects).
SwIntendedResolution – Number that describes the resolution of a data element in a preliminary phase of development, when a CompuMethod is not defined yet, which ultimately will specify its conversion formula using this value as a suggestion for the expected data resolution.
SwInterpolationMethod – Keyword that describes the mathematical method applied for interpolation, related to the interpolation routine that will be invoked.
SwIsVirtual – Boolean that denotes a virtual object, which is not part of the memory, and their derivation is reliant on other objects, requiring a swDataDependency.
SwPointerTargetProps – Aggregation of a single SwPointerTargetProps, denoting this element is a pointer to another object.
SwRecordLayout – A single reference SwRecordLayout related to this data object, which indicates how the data object is stored within the ECU memory.
SwRefreshTiming – The aggregation of a MultidimensionalTime which indicates update frequency for this element. This timing can then be collected by the tasks where this element is written, or it can be used in early development stages to specify a desired refresh timing or later stages to denote the actual timing.
SwTextProps – Aggregation of a single SwTextProps meta-class, specifying the text-related properties of this element.
SwValueBlockSize – If the data object is a value block (VAL_BLK), it indicates its size.
SwValueBlockSizeMult – If the data object is a value block (VAL_BLK) and has more than one dimension (otherwise it is not defined), it specifies its size throughout each dimension, via mulitple numbers. The sizes should be present from ascending order regarding the dimension.
Unit – Reference to a physical Unit associated with this data object. It can be used without a CompuMethod, but if both co-exist and the CompuMethod specifies a unit, then they must be compatible.
ValueAxisDataType – A reference to an ApplicationPrimitiveDataType attribute, which is a primitive data type that defines a set of allowed values and represents the primitive data type of the value axis within a compound data type, such as a CURVE or a MAP. It takes precedence over the compuMethod, unit and baseType attributes.

Use Cases and Precedence of SwDataDefProps Attributes

Different attributes may be required, optional, ignored or not even defined within one of the classes that aggregates SwDataDefProps, and upstream attributes can be either overwritten or added to the definition of sub-classes, according to different priority settings.

As you will see, SwDataDefProps can be defined for a type, prototype, instantiation, data access and calibration support. The normal use case in terms of precedence, the ones closer to the implementation will overwrite the previous elements. Some exceptions apply, as you have seen, but this is the conclusion.

The precedence chain, from lowest to highest is ApplicationDataType, ImplementationDataType, DataPrototype, InstantiationDataDefProps, ParameterAccess, FlatInstanceDescriptor and McDataInstance.

These relations are outlined in the table below, where the properties not mentioned for the meta-classes that aggregate SwDataDefProps are considered not applicable:

Attribute	Applicability on Different Meta-Classes
`additionalNativeTypeQualifier`	Defined on `ImplementationDataTypes` and `SwServiceArgs` independently of other definitions. Self-contained definition for `McDataInstances`. `DataPrototypes` inherit the definition from `ImplementationDataTypes`.
`annotation`	Defined by `ApplicationDataTypes`, `SwServiceArgs` and `SwSystemConsts` independently from other definitions. `ImplementationDataTypes`, `DataPrototypes`, `InstantiatonDataDefProps`, `ParameterAcceses`, `McDataInstances` and `ComSpec.NetworkRepresentation` add to the definitions of the preceding elements and `ApplicationDataTypes`.
`baseType`	Defined by `ImplementationDataTypes`, `SwServiceArgs` and `ComSpec.NetworkRepresentation` independently from other definitions. Self-contained definition for `McDataInstances`. `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccess` inherit the definition from `ImplementationDataTypes` and their preceding elements. Attribute is ignored for `SwSystemConsts`.
`compuMethod`	Defined for `ApplicationDataTypes`, `SwSystemConsts` and `ComSpec.networkRepresentations` independently from other definitions. Self-contained definition for `McDataInstances`. `DataPrototypes`, `InstantiationDataDefProps` and `SwServiceArgs` inherit their definitions from their preceding elements. `ImplementationDataTypes` and `FlatInstanceDescriptors` inherit the properties from preceding elements (if applicable) and its definition adds additional information.
`dataConstr`	Defined for `ApplicationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `SwServiceArgs` and `SwSystemConsts` independently from other definitions. `ParameterAccesses` inherit the element from preceding elements. `ImplementationDataTypes` using this definition constrain their sub-elements. Self-contained definition for `McDataInstances`.
`displayFormat`	`ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `SwServiceArgs` and `SwSystemConsts` define the element independently from other definitions. `ParameterAccess` inherits the definition from preceding elements. Self-contained definition for `McDataInstances`.
`displayPresentation`	Defined for `ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes` and `InstantiationDataDefProps` independently from other definitions. Self-contained definition for `McDataInstances`.
`implementationDataType`	`ImplementationDataTypes` and `SwServiceArgs` define the element independently from other definitions. `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` inherit their definition from preceding elements.
`invalidValue`	`ApplicationDataTypes`, `ImplementationDataTypes` and `ComSpec.networkRepresentation` define the element independently from other definitions. `DataPrototypes` and `InstantiationDataDefProps` inherit their definition from preceding elements. Self-contained definition for `McDataInstances`.
`stepSize`	`ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `ParameterAccesses` and `FlatInstanceDescriptors` define the element independently from other definitions. Self-contained definition for `McDataInstances`.
`swAddrMethod`	`ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `FlatInstanceDescriptors` and `PerInstanceMemories` define the element independently from other definitions.
`swAlignment`	Defined for `ImplementationDataTypes`, `DataPrototypes` and `InstantiationDataDefProps` independently from other elements.
`swBitRepresentation`	Defined for `McDataInstances` independently from other elements.
`swCalibrationAccess`	Defined for `ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `SwServiceArgs`, `FlatInstanceDescriptors` and `SwSystemConsts` independently from other elements. Self-contained definition for `McDataInstances`.
`swCalPrmAxisSet`	Defined for `ApplicationDataTypes` independently from other element definitions (except for the sub-elements `swCalprmAxis`, `swAxisGrouped.swCalprmRef`, `swCalprmAxisSet.swCalprmAxis` and `SwAxisIndividual.swVariableRef`, which are not defined). Inherited from preceding elements for `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses`. The sub-elements `swCalprmAxis`, `swAxisGrouped.swCalprmRef`, `swCalprmAxisSet.swCalprmAxis` and `SwAxisIndividual.swVariableRef` are defined for `InstantiationDataDefProps` and `ParameterAccess` independently from other definitions. Self-contained definition for `McDataInstances`.
`swComparisonVariable`	Defined for `ParameterAccess` independently from other elements. Self-contained definition for `McDataInstances`.
`swDataDependency`	Defined for `DataPrototypes` and `InstantiationDataDefProps` independently from other elements. Self-contained definition for `McDataInstances`.
`swHostVariable`	Defined for `McDataInstances` independently from other elements.
`swImplPolicy`	Defined for `ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes` and `SwServiceArgs` independently from other elements.
`swIntendedResolution`	Defined for `ApplicationDataTypes` independently from other elements, but only in early stages of development, as a reference to the development of `CompuMethods`.
`swInterpolationMethod`	Defined for `ApplicationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` independently from other elements. Definition inherited from preceding elements for `ImplementationDataDefProps`. Self-contained definition for `McDataInstances`.
`swIsVirtual`	Defined for `DataPrototypes` and `InstantiationDataDefProps` independently from other elements. Self-contained definition for `McDataInstances`.
`swPointerTargetProps`	Defined for `ImplementationDataTypes` and `SwServiceArgs` independently from other elements. Definition inherited from preceding elements for `DataPrototypes`.
`swRecordLayout`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited from preceding elements for `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses`. Self-contained definition for `McDataInstances`.
`swRefreshTiming`	Defined for `ApplicationDataTypes`, `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps`, `SwServiceArgs`, `FlatInstanceDescriptors` and `McDataInstances` independently from other elements.
`swTextProps`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited for `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` from preceding elements. Self-contained definition for `McDataInstances`.
`swValueBlockSize`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited for `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` from preceding elements. Self-contained definition for `McDataInstances`.
`swValueBlockSizeMult`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited for `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` from preceding elements. Self-contained definition for `McDataInstances`.
`Unit`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited for `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `ParameterAccesses` from preceding elements. Self-contained definition for `McDataInstances`.
`valueAxisDataType`	Defined for `ApplicationDataTypes` independently from other elements. Definition inherited for `ImplementationDataTypes`, `DataPrototypes`, `InstantiationDataDefProps` and `SwServiceArgs` from preceding elements. Self-contained definition for `McDataInstances`.

Closing Notes

I know, this article hsa been heavy on meta-classes and attributes, which is not always easy to accompany. But in the case of such an important meta-class, such as SwDataDefProps, which contains (in my opinion, too many) attributes that do not apply to all the meta-classes that aggregate it, things can become confusing. Nonetheless, do not underestimate its potential and keep these rules close by when creating and analysing ARXML models, you will thank me for it.

If you fancy more content of the same kind, have a look into our website. This is an ever-growing library for Autosar. Soon, an eBook will be added into the mix, where much more content like this will take part. Make sure to place yourself on the waiting list!

Author: Micael Coutinho (opens in a new tab)

References:

Software Component Template - Autosar Specification (opens in a new tab)