[AUTOSAR com 2. Advanced introduction to communication protocol stack]

First of all, understand Autosar Communication stack diagram

AUTOSAR The communication stack in contains the following parts ：

One .can

We are looking at and Autosar Can Model

·CAN drive

CAN The driver provides a unified interface for upper users ——CAN Interface .CAN The driver hides the correlation as reasonably as possible CAN Hardware specificity of the controller .

CAN Driver is the bottom part , Perform hardware access for the upper layer and provide hardware independent API. The only one in the upper layer can access CAN Driven by CAN Interface .

If a few CAN The controller belongs to the same CAN Hardware unit , Then they can be made by CAN Drive to control .

One CAN The controller is always associated with a physical channel . It is allowed to connect with the physical channel on the bus , No matter CAN Whether the interface will be relevant CAN Controllers are treated separately .

·CAN Interface （ Hardware abstraction ）

CAN Interfaces provide standardized interfaces , adopt ECU Of CAN Bus system to support communication . Its API And dedicated CAN Controller and its pass CAN The access of the driver layer is irrelevant .CAN Interfaces can access one or more through a unified interface CAN drive .

CAN The interface can only be used for CAN signal communication , And it is to operate one or more underlying CAN Driven and specially designed . Covering different CAN Several hardware units CAN The drive module consists of a driver in CAN Drive the general interface specified in the specification to represent .CAN outside （ That is to say LIN） Other protocols of do not support .

·CAN Transport layer

CAN The transport layer is located at PDU Routing and CAN Modules between interface modules . Its main function is to split and merge more than 8 Bytes of CAN I-PDU.

according to AUTOSAR Basic software architecture ,CAN The services provided by the transport layer include ：

n Data segmentation in sending direction ;

n Data merging in the receiving direction ;

n Data flow control ;

n Error detection during segmentation .

AUTOSAR The architecture defines each specific transport layer of the communication system （CanTp、 contain LinIf Of LinTp、FlexRayTp）. therefore ,CAN The transport layer only covers CAN Details of the transmission protocol .

CAN The transport layer has an interface , This interface connects a separate lower layer CAN Interface layer and a separate upper layer PDU Router modular .

according to AUTOSAR Released plan , The CAN The transport layer specification contains the following limitations ：

• CAN The transport layer only operates in event triggered mode ,

• No transmission / Receive undo .

·CAN Transceiver drive （ and NM Strong correlation ）

CAN The transceiver driver is responsible for processing ECU Upper CAN Transceiver , Based on the whole ECU Bus specific to the current state NM The state of .

CAN The target driven by transceiver ：CAN Transceiver driver Abstract use CAN Transceiver hardware chip . It provides hardware independent interfaces to higher layers . It can also pass through MCAL Layer of API from ECU Abstracted from the design , visit CAN Transceiver hardware .

CAN The hardware of the transceiver must provide functions and interfaces , To map to AUTOSAR CAN On the operation mode model driven by transceiver .

Lower drive （SPI and DIO） The use of API Must synchronize . The implementation of lower drivers that do not support synchronous behavior cannot be compared with CAN Used with transceiver driver .

Two COM

AUTOSAR COM This layer is located in RTE and PDU Between routers . It comes from OSEK_COM standard .AUTOSAR COM It provides the function of signal gateway .

COM The dependencies with other modules are shown in the following figure ：

·COM Manager

COM Manager（COM management ） It's basic software Basic Software（BSW） A component of . It is a resource management that includes the control of lower level communication services .

COM Manager Basic software module of control （BSW） Communication related , Not related to software components or runnable entities .

COM Manager Collect bus communication access requests from the communication requester , And coordinate bus communication access requests .

COM Manager The goal is ：

（1） Simplify the use of bus communication stack for users . This includes initialization of bus communication stack and simplified network management processing .

（2） Coordinate with multiple software components （ In a ECU On ） Irrelevant bus communication stack （ Allow the transmission and reception of signals ） The usability of .

（3） Temporarily cancel the signal transmission to prevent ECU Wake up communication bus .

（4） control ECU More than one communication bus channel , This is achieved by implementing a state mechanism for each channel .

（5） To provide for ECU Keep the bus in “ Silent communication ” Pattern .

（6） Simplify resource management by allocating all resources necessary for the request communication pattern .

COM Manager It contains the following basic functions ：

·AUTOSAR COM And OSEK COM Comparison

According to the functions provided by the communication part , Compare the two in the same function API, And their unique API, because AUTOSAR COM in comparison with OSEK COM, There is one more COM Manager, Communication management module , So the whole thing AUTOSAR COM Manager by AUTOSAR Unique to the standard , Next, the same functional parts of the two are compared .

1、 Same functions and services

（1） Start and control services

The comparison between the two in the start-up and control service part of communication can be seen ： First ,AUTOSAR Provided API More , It shows that its function is strong ; secondly ,AUTOSAR The startup and control service of includes I-PDU（ Interaction layer protocol data unit ） Processing and control of , Such as Com_IpduGroupStart、Com_IpduGroupStop.

（2） Communication services

By contrast, we can see ,OSEK The communication service includes some simple handling of errors , Such as getting the wrong service Id（COMErrorGetServiceId）, and AUTOSAR The communication service still includes a pair of I-PDU To deal with , Such as Com_TriggerIPDUSend.

（3） Notification mechanism support services （OSEK） And callback notification service （AUTOSAR）

2、 Different functions and services

（1）OSEK by I-PDU The processing of provides a special kind of service , be called OSEK Indirect network management interface , contain 2 individual API：I-PDU Transmission instructions （I_MessageTransfer） and I-PDU Timeout indication （I_MessageTimeOut）.

（2）OSEK The communication part provides some routines to expand the communication , contain 3 individual API：StartCOMExtension、COMCallouts、COMErrorHook.

（3）AUTOSAR Some scheduling functions are provided , It mainly routes the receiving or sending of messages or signals 、 The role of scheduling , contain 3 individual API：Com_MainFunctionRx、Com_MainFunctionTx、Com_MainFunctionRouteSignals.

（4）AUTOSAR The communication part of has a COM Manager, This is a communication management module , yes AUTOSAR Standard specific , Mainly responsible for monitoring communication 、 management 、 Diagnose and manage communication related ECU state . The following table lists the parts it provides API.

summary ： AUTOSAR COM And OSEK COM The difference is comM
comM The role of ：1. For communication mode , Manage communication resources 2. Simplify the use of bus communication stack for users , Including initialization of bus communication and simplified network processing