Common Terms Used In AUTOSAR
Signal
AUTOSAR implements signal based communication. A signal is the smallest amount of information that a CAN message can have.
A signal can be of any size from 1- bit to all 64 bits of CAN message (considering the CAN message is 8-Bytes), in other words the CAN message is divided in bits called signals.
Signals can be also there for FlexRay or other bus, the only change is maximum amount of signals it can hold.
To relate this, lets consider a real life example.
1. Suppose a ECU needs to know the state of doors (locked/unlocked).
In normal C program we would implement a flag which will indicate the state of the doors. But in AUTOSAR, a 1-bit signal is used to indicate this.
2. Suppose your application needs to transmit numeric information in having a range of 0 – 7 so a 3 bit signal is enough.
In this way, signal implementation helps in saving the space required by information in the CAN data field by using only the space required for information.
SWCs use signal to communicate with each other by using VFB via RTE. Signal is implemented and only understood by layers from COM to application Layer.
Signals can be grouped when signals needs to be kept tightly with each other ,or signal groups can be used to support complex data structure like structs.
PDU Or Message
In AUTOSAR, roughly(粗略地) a message is called PDU (Protocol Data Unit). I am saying roughly because, PDU contains information other than our data which is used or extracted by below or upper layers in transmission or reception respectively.
There can be n number of PDUs with varying size. The PDU is basically group of packed signals, along with lower layer information.
AUTOSAR COM performs the packing or unpacking of signals in or from PDU, while transmission or reception respectively.
Every PDU has a unique identifier associated with it.
PDU contains SDU and PCI.
SDU is the abbreviation of Service Data Unit.
PCI is the Protocol Control Information.
SDU is the data which needs to be transmitted.
While transmission, SDU is passed from upper layers to lower layers along with PCI. During reception,
SDU is the data extracted from below layers and passed on to upper layers.
PCI contains the information which indicates the next destination of the SDU.
Basically, it contains the source and destination of the SDU.
The source and destination in this case is the next layer to which the PDU needs to be passed.
While transferring PDU from layer to layer, its called by relevant names based on layer it is in.
So, The PDUs are named as: I-PDU (Interaction Layer PDU), N-PDU (Network Layer PDU), L-PDU (Data Link Layer PDU).
Whenever the PDU is in, layers above Communication Hardware Abstraction layer, then its called I-PDU.
Whenever the PDU is in, layers below PDUR and above Communication Drivers layer, then its called N-PDU.
Whenever the PDU is, below Communication Hardware Abstraction, then its called L-PDU.
Computation Method
There are mainly three categories of compu methods:
- Linear: During configuration, we have to give ranges of raw values. Like minimum this value can be, maximum this value can go,Factor (which is the multiplication factor or its also called gain),Offset value.
- Text Table: It is most simple type of compu method. It is a table of numerical values which represent some text which has some meaning.
- Scale-Linear: It is a table of linear compu methods.
.Cdd File
.cdd file is a Vector specific file which has information of Diagnostics-configuration related information.
Though it is vector specific but many tools are using it as standard.
This file is used in CandelaStudio application which is by Vector.
SIP
Software In Package is a term used by AUTOSAR engineers using Vector DaVinci Tool.
It is a package of all the libraries and files useful for developing AUTOSAR software using Vector tools.
OSEK/VDX
OSEK is abbreviation of Offene Systeme und deren Schnittstellen für die Elektronik in Kraftfahrzeugen in german,
but in English it is : Open Systems and their Interfaces for the Electronics in Motor Vehicles.
French automotive companies, like Renault and PSA Peugeot Citroën, had similar project called VDX (Vehicle Distributed Executive).
Therefore, the name OSEK/VDX is used in combination.
Composition SWC
Composition is nothing but a group of SWCs which is assigned to a single ECU during System Configuration.
This grouping is logical, it means there is no memory used in such grouping.
SWC
A SWC or software component is a component which has application logic. In AUTOSAR a functionality is encapsulated by a SWC.
For example, power window operation in a car, for this a dedicated SWC will perform this functionality.
SWCs communicate with each other or use lower layers by using ports with the help of RTE.
AUTOSAR has categorized SWCs based on its use into following types:
- Application SWC: This is normal SWC which has only application or part of it.
- SensorActuator SWC: It is a special type of SWC which handles sensors or actuators.
- Parameter SWC: This SWC is used for sharing the calibration parameters of (ECU on which it is situated) to external devices.
- These SWC don’t have any internal behavior unlike Application SWC or SensorActuator SWC.
- Composition SWC: discussed above.
- Service Proxy SWC: It acts as a proxy to provide internal services to one or more remote ECUs.
- Its main use is to distribute the mode information of vehicle throughout the system.
- Service SWC: It provides services specified by AUTOSAR of BSW module.
- ECU Abstraction SWC: This type of SWC provides access to I/O by directly interacting with specific BSW modules.
- Other SWCs cannot be used for accessing the I/O, only this can be used.
- Complex Device Driver SWC: This SWC is used to develop complex device drivers (CDD) for external devices which AUTOSAR don’t support or have some time critical operations.
- Nvblock SWC: This SWC is used when interacting with NVRAM or memory.
