Design scheme of automotive electronic control system unit

summary

In order to meet the cost of the next generation of automotive electronic control system units, the PCB space has limited requirements for high performance, high reliability and high stability. This paper designs a 16-bit Freescale MCU MC9S12XF512 as the main control chip of the automotive electronic control system unit. It is based on the FlexRay bus technology and targets the body layout and body control requirements. This paper introduces in detail the design of the automotive electronic control system structural unit, including the main control chip of the control module, the hardware design and software design process of the FlexRay bus communication module and its peripheral circuits. Through actual design and development, multiple automotive electronic control system units were produced, and communication tests based on the FlexRay bus were realized through software programming. The control unit of this design has an independent bus controller, which can be easily connected to other ECUs for high-speed data transmission.

I. Introduction

Nowadays, the automotive electronic technology is developing faster and faster. The traditional automotive bus system can no longer meet the reliability requirements of high-speed transmission in automobiles. With the emergence of automotive electronic control units (ECUs), the requirements for large-capacity data information to be shared between multiple subsystems are getting higher and higher, and the requirements for the real-time and reliability of information transmission in automotive control systems are also getting higher and higher. The popular automotive bus network currently consists of LIN bus, CAN bus network and the latest FlexRay bus network, while the in-vehicle Ethernet bus network is only mentioned. There is no in-vehicle Ethernet at present, and only a few European institutions have developed it. The actual application of FlexRay network is not mature today and is not popular in China. Relatively speaking, among the in-vehicle network buses, CAN bus is the most widely used, and the application technology is relatively mature and complete.

However, in some important links of the automotive electronic control system, especially those with extremely high real-time requirements for transmission speed and security, the network and CAN in the automotive electronic control system can no longer meet the requirements. Therefore, the design of an automotive electronic control system based on the FlexRay bus unit is very meaningful.

Based on FlexRay bus technology, this paper designs an electronic control system unit that can be applied to vehicle speed control in network systems.

II. Design of FlexRay communication module of electronic control system unit

Based on the FlexRay bus protocol and FlexRay communication principle, the electronic control system design of the device is mainly composed of FlexRay bus transceiver and microcontroller, independent bus interface and some peripheral circuits. The general FlexRay communication system uses the FPGA module of the PCI chip to control the MFR4310 and realizes the data transmission of the FlexRay bus node through the TJA1080 chip. However, this FlexRay communication system is large in size and costly, and the hardware circuit module is relatively complex. Therefore, this paper adopts an embedded automotive electronic control system unit composed of the FlexRay bus interface controller MC9S12XF512 chip and the TJA1080ATS/2 bus driver circuit and some peripheral circuits. As an independent bus FlexRay communication regulator, the MC9S12XF512 microcontroller chip contains three parts, namely the FlexRay communication controller, the speed 12 core and the independent bus controller. The FlexRay bus transceiver TJA080ATS/2 contains two parts, namely the bus driver module and the bus monitoring module. The hardware diagram of the FlexRay communication module is shown in Figure 1.

Figure 1 FlexRay communication module hardware diagram

MC9S12XF512 MCU is a new automotive MCU of Freescale embedded dual-channel FLexRay V2.1 series, with the characteristics of high speed, low power consumption, high stability, low price, small size, etc., and has 2-channel FlexRay. Practice has proved that the FlexRay communication module using MC9S12XF512 and TJA1080ATS/2 has strong peripheral expansion capability, strong anti-interference ability, small size, and has the characteristics of high performance, high reliability and stability.

The specific introduction of the electronic control system unit is shown in Figure 2. It is mainly composed of the minimum system module controlled by a single-chip microcomputer, a dual FlexRay bus transceiver circuit module, a clock module, a reset and BDM debug interface circuit module, a power module and an independent bus interface circuit module.

Figure 2 Hardware structure diagram of electronic control system unit

A.FlexRay communication module

The FlexRay communication module is composed of the FlexRay bus interface of the microcontroller MC9S12XF512 and the circuit composed of the dual FlexRay transceiver TJA1080ATS/2 of NXP and some filter capacitors and resistors. This paper designs two paths for the FlexRay bus communication module. One path is connected with the TXD pins of PH1 and PH2, PH5, PJ5, PH3, and PJ3 on the microcontroller and the FlexRay bus transceiver, TXEN, RXD, RXEN, and ENSTBN. The other path is connected with another TJA1080ATS/2 pin through the six port pins of the microcontroller PH4, PH5, PH6, PH7, PJ4, and PJ6. The two ways are connected to the output of the FlexRay bus and the B node of the FlexRay bus through the filter circuit respectively, and the two nodes realize the data communication of the FlexRay bus. The filter circuit is designed to increase the electromagnetic interference and anti-interference capabilities of the FlexRay bus communication module.

B. Peripheral modules

The peripheral modules include clock circuit, power circuit, reset circuit module and BDM.

There are many solutions for power supply circuits. The power supply circuit built with LM2940 in this article is used to provide power supply voltage to microcontrollers, clocks, FlexRay bus transceivers, etc.

The clock circuit is mainly used to provide sufficient clock frequency to the single-chip microcontroller so that the single-chip microcomputer can work at high speed.

The reset and BDM circuits mainly use the background debugging mode (BDM) function of the microcontroller. Without the need for a simulator, all hardware breakpoints, conditional breakpoints, online debugging, and bus debugging can be realized, providing convenience for writing and debugging FlexRay on the bus for the microcontroller program.

C. Independent bus interface module

The independent bus interface module is mainly used to connect the single-chip microcomputer with external sensors, actuators, etc., and the independent bus interface circuit is mainly used to realize the driving and bus signal matching functions.

III. Software design of electronic control system unit

The design of the automotive electronic control system unit in this paper mainly uses the MC9S12XF512 chip as the application software. The FlexRay bus communication of each electronic control unit is developed and programmed. The default FlexRay trigger mode is based on time-triggered bus communication. The microcontroller can issue corresponding instructions through polling or interrupt-driven mode for the internal FlexRay controller to process data. Figure 3 is a complete FlexRay bus communication unit development and programming hierarchy.

Figure 3 Development and programming structure of FlexRay bus communication unit This design sends the data time slot rules to the FlexRay bus node regularly in the FlexRay car body according to the rule set and the requirements of the FlexRay bus protocol, and obtains the required FlexRay bus node time slot data as needed. Although the program of each electronic control system unit is different, the general functions of the setting and initialization of the FlexRay communication module are consistent, which can be divided into: initialization setting, sending data, and receiving data.

A. Initialization Procedure

The initialization module includes the phase-locked loop (PLL) initialization module, the FlexRay system initialization module, the real-time interrupt module initialization, the FlexRay system clock module initialization, and the input/output module initialization. In the interrupt-driven mode, the FlexRay system initialization module of the automotive electronic control system unit includes: the FlexRay controller can forcefully enter the node configuration state, initialize the protocol configuration parameters of the FlexRay controller, initialize all message buffers, set callback functions and timers, end the node configuration state, initialize startup, initialize the message buffer to 0, start, start timer T1, start the corresponding interrupt of timer T2, etc. The FlexRay initialization flow chart is shown in Figure 4.

Figure 4 FlexRay initialization flow chart unit

B. Send data program

After the microcontroller and FlexRay module are successfully initialized, it can be used to send or receive the corresponding FlexRay node ID slot data information. The microcontroller accurately provides specific information through the FlexRay bus transceiver node. Implementation process: The single-chip microcontroller will send an ID number data information for each time slot according to the data format of the FlexRay protocol, write the data information of the sending time slot into the buffer area; send the function instruction to start sending and the time slot node information to the bus. The FlexRay data flow diagram is shown in Figure 5.

Figure 5 FlexRay data transmission flow chart