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. 

 

标签：layers,information,AUTOSAR,Used,Terms,SDU,PDU,layer,signal
来源： https://www.cnblogs.com/JasperZhao/p/16683746.html