CAN Bus Gateway On Vehicle

With the development of electronics technique and its wide application on vehicles,there are more and more electronic equipments on automobiles. Although the ECU systemimproves the dynamics, economy and comfort, it raises other problems such as body wiringcomplexity, space constraints and some reliability issues. In order to solve the datatransmission security, reliability and vehicle weight increasing problems as well as satisfythe needs of the wire-control automobiles, vehicle body network and bus technology hasgenerated and developed enormously. Vehicle network has many advantages such assignificant reduction of wiring harness, reduction of body weight and costs, improvementof the efficiency of fault diagnosis and enhancement of the level of intelligent control.At present, some vehicle buses have already been put into use, such as CAN bus, LINbus, MOST, and Flexray. Different applicants can select proper one to achieve theirpurposes. Compared with other vehicle buses, because of the good network transmissioncharacteristics and low cost, CAN bus is considered as the most popular solution for vehiclenetwork.With the function diversity in vehicle electronics, vehicle network is becoming moreand more important. So the system overall complexity show liner growth and theconsequences are the enormously increasing volume of data. A powerful vehicle networksare bound to respond to these growth. The core of the vehicle networks is router, also calledgateway. The gateway's main responsibility is transmitting data to all the ECUs on thevehicle and meanwhile monitoring the system. Besides, it also has the fault diagnosisfunction. Equipments on the vehicles have different transmission delay sensitivity. Enginecontroller, AMT, ABS, and airbag require strict real-time performance and the lightswitches, door switches and seat adjust have little requirements on real-time performance.If all these nodes are attached to high-speed bus, it must be a big waste. So the multi-busdesign is necessary. Vehicle driver system uses the high-speed CAN with transmission ratebetween 500Kbps-1M bps; vehicle body system uses low-speed CAN with transmissionrate equal to 250Kbps. The main objects of low-speed CAN are lights switches, electricseat control switches and anti-theft control switches. These parts don't have manyrequirements on real-time performance but have large quantity, so the driver system isseparated from these parts to ensure its real-time performance. On the other hand, the usingof low-speed CAN can increase bus transmission distance, improve anti-interference ability,reducing hardware costs.Two type of CAN bus are independent from each other. They exchange data and sharethe resource through gateway server. As the core of vehicle management system as well asthe basement of vehicle general control, the main task of MCU is to analyze and deal with avariety of information, issue instructions and coordinate the various control units and automotive electrical equipment.Automobile self has complex electrical characters and large quantity of electric controlequipments. The vehicle running performance, location, diversified vehicle body parts state,diagnosis information and other important information can be accessed and accessed tothrough different vehicle bus network and all of this information is needed by vehiclegateway service system.In this paper, a new simple function gateway, which meets the communicationrequirements of nodes on the bus, is developed to satisfy the vehicle network'sdevelopment. According to the CAN bus function and ECU location characteristics, theECUs on the vehicle are divided into five classes, they are power system, comfort system,diagnosis system, information system and appearance system. Power system is responsiblefor AMT's intelligence control and dealing with related data; comfort system is responsiblefor vehicle body control, vehicle multimedia and air-conditioner; diagnosis system isresponsible for the vehicle fault diagnosis; information system includes the vehiclenavigation and GPS; appearance system is responsible for dealing with the data needed byappearance board. The ECUs belonging to different CAN sub-systems on the vehicle arelinked together tightly by the gateway to realizing data exchange and resource sharing.The practical significance of this paper is that a 5-CAN-BUS gateway prototype hasbeen realized. And a more suitable protocol based on J1939 applied in this gateway isdefined too. The protocol covers physical layer, data link layer, network layer andapplication layer. The gateway has implemented basic functions of a common gateway:data forward, error control, flow control and address management. Error control depends onthe CAN protocol error control and recovery mechanisms; flow control utilizes the CTSframe flow control mechanism; address management use the self-defined mechanism basedon J1939.The main contents of this paper are as follows:( 1 ) Through careful reading and analyzing the J1939 protocol ,using the J1939 protocoldata frame format and classification methods and mending the protocol according toCAN gateway's specification, the protocol applied in this paper is defined;( 2 ) According to the protocol and through the requirements analysis of CAN gateway, Ihave designed the hardware circuit of the gateway, including the microprocessorselection, CAN interface design, BDM debugging interface circuit design and powermodule design. Finally, MC9S12XDP512 is chosen as the microprocessor;PCA82C250 is chosen as the CAN transceiver; BDM interface is a 6-pin socket withone pin connected to BKGD pin on the microprocessor; according to the differentvoltage requirements of the modules of the microprocessor, the power supply has twolevel voltage supply; first level is 12v to 5v converted by 78M05, the second is 5V to2.5V converted by SIPEX1117.( 3 ) The paper completed the software design of the gateway. The concept of passage isintroduced in order to support the virtual link between the gateway and a node andmulti-channel data transmission; by using the PTI timer, the length of timer can be changed flexibly; the CAN transmit and receive interrupt vector and PTI timercounting interrupt vector are defined and the interrupt service routines are programmedtoo; according to gateway system's requirements, the main task is divided into seventhread and are scheduled by the preemptive round-robin algorithm.