AUTOSAR COM
The road below COM
COM never touches a wire. It hands packets to one neighbour and gets packets from that neighbour. Here is the whole road, for CAN and for Ethernet.
Layers, each with one job
The software in a control unit is built in layers. Each layer talks only to the one above and the one below. That is why COM can be the same on every bus: everything specific to a bus lives further down.
| Layer | Its one job |
|---|---|
| Application | The actual function: compute, decide, display. |
| RTE | The switchboard between applications and everything else. |
| COM | Signals in and out of packets, and when. This course. |
| PDU Router | A sorting office. Looks up where each packet goes. Never looks inside. |
| Bus-specific layers | Turn a packet into what this bus needs, and drive the hardware. |
Walk the road
Pick a bus and a story, then click through it.
The handful of calls at COM's borders
All traffic between COM and its neighbours goes through a few calls. If you ever read real COM code or a trace, these are the names you will see.
| Call | Direction | Meaning |
|---|---|---|
Com_SendSignal | from above into COM | "Here is a new value for this signal." |
Com_ReceiveSignal | from above into COM | "Give me the current value of this signal." |
PduR_ComTransmit | COM to below | "Send this packet." |
Com_TxConfirmation | from below into COM | "Your packet is on the bus." |
Com_RxIndication | from below into COM | "A packet arrived for you." |
Com_TriggerTransmit | from below into COM | "I am about to send. Give me the packet's content now." |
Big packets that travel in pieces (lesson 13) use a second set of calls for starting, copying piece by piece, and finishing.
Two notes on Ethernet
Same COM, different road
Below the PDU Router, the Socket Adaptor turns "send this packet" into "send these bytes over this network connection". COM itself does not change.
Service data often skips the packing
On Ethernet, data is often turned into bytes above COM, by a part called a transformer. COM then receives a finished block and passes it through, as in lesson 13.
Check yourself
Optional. Answer from memory.
The AUTOSAR words
| Plain word here | AUTOSAR word |
|---|---|
| The neighbour below COM, sorting office | PDU Router (PduR) |
| CAN layers | CAN Interface (CanIf), CAN Driver |
| Ethernet layers | Socket Adaptor (SoAd), TCP/IP stack (TcpIp), Ethernet Interface and Driver |
| Turning data into bytes above COM | Transformer, for example the SOME/IP transformer |
Sources: AUTOSAR COM specification, R25-11, section 7.8 and Table 7.7; Layered Software Architecture, R25-11, the communication stack and "Interaction of Layers" pages.