The development of in-vehicle communication technology ranges from serial communication to industrial buses to bus networks. With the increase of in-vehicle electronic control and information devices and the increasing demand for information services, the application of more advanced computer networks in vehicles is inevitable, especially multimedia information, as well as the application of electronic maps and Internet information in vehicles, like CAN Such a bus can only meet some functions, but it is difficult to meet the bandwidth and transmission form. From the current point of view, in-vehicle Ethernet has landed in various luxury car systems.
Due to the maturity and wide application of Ethernet technology, people will naturally think of using it to meet this part of the demand, but the current cost of hardware and software is relatively large, because of the vehicle environment and the network data transmission requirements on the vehicle, and Ethernet There is a big difference in the original design of the network. If you use Ethernet in a car, you must modify it appropriately. You must maintain the advantages and characteristics of Ethernet and meet the requirements of the vehicle environment. This is called on-board Ethernet.
Figure 1: Su Rui was cracking Tesla Ethernet data
According to the different data types in the network communication of the car and the transmission frame of the network communication, Su Ruide collects the data of the car Ethernet vehicle information communication. Taking Tesla as an example, Su Ruide already has the Tesla Model 3 network extension And the vehicle circuit diagram, obtain the left (L) right (R) body controller unit BCM, motor controller unit, and front body controller data through LIN, CAN, CAN-FD and Ethernet, as the vehicle control strategy data research, Data acquisition and acquisition development, teaching, vehicle network part 3 CAN, 4 LIN, although not worse than LBCM (5 CAN, 4 LIN), RBCM (10 CAN, 14 LIN (Ultrasonic radar occupies 12)), It's a lot of resources.
1. Information transmitted by vehicle-mounted Ethernet
The type of data information transmitted on the vehicle and the use requirements for these data determine the characteristics of the transmission network and are also the basis for the selection or design of the vehicle network standard. The data used and transmitted by the control system and information system on the vehicle can be divided into control Command parameters, safety and driving assistance information data, entertainment information (multimedia) data, information service data.
1. Control command parameters
1) Low-bandwidth control applications: These in-vehicle control subsystems require low bandwidth and low service quality requirements, including those in the car that do not strictly require safety control systems, such as electric mirror folding and electric seats chair.
2) Real-time control applications: these in-vehicle systems have relatively low bandwidth requirements, but have higher requirements and strong real-time performance, such as suspension and braking systems, ABS, and traction control systems. These services require relatively high quality of.
2. Safety and auxiliary driving information data
More and more modern cars are equipped with many built-in driving assistance safety systems, including adaptive cruise control systems using lidar or radar sensors, reversing radar and night pedestrian detection using infrared sensors. These data will affect driving safety. High reliability and real-time.
3. Entertainment information (multimedia) data
In addition to the traditional infotainment system, more and more video and audio devices are installed in the car, which transmit multimedia data, require higher bandwidth, and have higher quality of service requirements depending on the application, including some passive Safety systems, such as the 360 panoramic reversing camera for the driver, also include active safety systems, lane departure detection using front and rear optical cameras, these are also typical information transmitted in Ethernet
4. Information service data
In addition to the traditional positioning and navigation electronic map data, with the improvement of the connection between the vehicle and the Internet, and the ability to obtain information and upload information, the amount of data similar to the information transmitted by the traditional Internet network will increase significantly. Even in the vehicle-mounted environment, Ethernet is still a suitable transmission network for these data from the aspects of user use and industrial technology foundation, but because the current cost and R & D cost are too high, it has not been widely popularized.
Second, the performance of vehicle-mounted Ethernet
Compared with the traditional Ethernet application environment, the vehicle-mounted system has the following characteristics:
1) Small distribution range and high density.
2). The nodes have large differences and many data types. The requirements for data transmission bandwidth, real-time performance, and reliability are complex, and the variation range is wide.
3). Require industry technology and equipment standardization, open structure and flexible expansion.
4). There are higher requirements for hardware technical indicators and more sensitive to cost. Data collection, maintenance, wiring and collectable data lists and efficiency requirements in Ethernet data applications should be considered.
5). The hardware standard should not be too low. To meet the standards of the automotive industry, the reliability, use of environmental parameters, electromagnetic compatibility, environmental protection, and low power consumption are required to be as high as possible.
Third, the advantages of using Ethernet
Although the original intention of Ethernet design is not a network applied in the vehicle environment, but due to its technology and application foundation in the field of computer networks, as well as the technical development and application requirements on the vehicle, the Ethernet has some other standards that cannot be compared with the vehicle. Advantages, mainly in the following aspects:
1. The technology is mature, and the development and production of software and hardware have a foundation, which can shorten the R & D and production cycle, improve efficiency, and reduce costs.
2. The application function is easy to interface with other systems. Various network-based information application technologies and products can be transplanted to the vehicle-mounted system, similar to installing a computer.
3. In line with the development trend of in-vehicle information technology, the interconnection of the Internet of Vehicles and the Internet of Things in the future must rely on Ethernet technology, combined with 5G, and there can be endless imagination in the future.
4. It is conducive to the entry of mature IT technology into the automobile industry and promotes the development of in-vehicle information technology, vehicle informatization and intelligence.
5. Users who are already familiar with Ethernet are more likely to accept information service functions and systems based on in-vehicle Ethernet.
6. It is conducive to the intelligentization of vehicles and the promotion of various information technology-based vehicle safety technologies, and has since opened the era of software-defined cars.
7. The hardware technology and cost that support the physical layer requirements of in-vehicle Ethernet have been verified. Some applications of in-vehicle Ethernet systems have verified the feasibility of using Ethernet in vehicles to build in-vehicle networks, such as Porsche ’s in-vehicle wireless terminals:
Figure 2: Porsche Gateway integrated Ethernet
4. Hardware supporting on-board Ethernet
With the development of in-vehicle Ethernet technology, while continuously improving the relevant protocol standards, hardware circuits supporting in-vehicle Ethernet have also been continuously developed. The hardware circuit of the vehicle-mounted Ethernet can also be divided into two categories, one is the vehicle-mounted Ethernet communication medium chip, and the other is the processor that supports the vehicle-mounted Ethernet communication protocol. Compared with the general Ethernet, the vehicle-mounted Ethernet is characterized by the use and The storage temperature range, electromagnetic compatibility and other aspects meet the automotive environmental requirements. Based on the expectations of the potential development of in-vehicle information technology and products, not only traditional in-vehicle electronic component manufacturers have actively developed in-vehicle Ethernet technologies and products, but some companies in the network industry have also actively participated in the research and development of in-vehicle Ethernet.
Figure 3: Terminals supporting Ethernet data collection and transmission ( Sui Ruide V81 )
Maywell and Mindray Semiconductor released standard Ethernet-based physical components for in-vehicle networks in 2012; Freescale launched the AVB iMX 6 series of application processors for in-vehicle infotainment systems and integrated in-vehicle information services The design of the infotainment platform provides convenience, and supports the development of real automotive Ethernet AVB through hardware and Ethernet switch solutions; SureTech developed the V81 series of TBOX products based on iMX 6, which is used in a large number of library functions Vehicle control strategy, CAN message collection and transmission, 5G and IoV terminal; Xilinx and Harman International Group Co. developed the CORETM IP core for field programmable gate array (FPGA) platform; NXP launched a vehicle-oriented Ethernet network The product portfolio of transceiver TJA1100 and Ethernet switch SJA1105 has many hardware functions required by in-vehicle Ethernet, which meets the standards specified by the OPEN Alliance; Broadcom ’s new BCM89811 physical transceiver is used in infotainment systems, advanced driver assistance systems, And telematics, instrument cluster, car audio host and Vehicle station module connected to Ethernet has wide application scenario; Renesas vehicle information terminal SOC R-CAR series, and in-vehicle AV BZ / A series has been achieved the support of the vehicle Ethernet AVB.
Five, the basic process of Ethernet access
There is no difference between the master and slave nodes in Ethernet. In order to coordinate the transmission of information through the network line, the CSMA / CD mechanism is used to obtain the right to use the bus. The basic working process is as follows:
1. A node wants to send data through the network, first check whether the network is "idle" (there is no data in the network in the transmission state), if the network is "busy" (the data is in the transmission state in the network), then continue to query and wait.
2. When the network is idle, the node starts to send data. At this time, there may be multiple nodes waiting for this "idle" moment, and once "idle", they will start to send their own data.
3. If the sending node judges that there is "obstruction", the sending of data will be interrupted and the sent data will also be deleted. After a random wait, the network resumes a round of data transmission.
The CSMA / CD network access method requires that the range of the Ethernet network is limited to control the maximum transmission time of data packets. The data packet parameters are as follows:
Table: Ethernet packet parameters:
| Serial number |
Field name |
Length / B |
effect |
Explanation |
|
1 |
Preamble |
7 |
Network nodes maintain synchronized clock pulses |
The combination of preamble and delimiter has the function of clock synchronization |
| Frame start delimiter |
1 |
Packet start flag |
||
| 2 |
target address |
6 |
MAC address of the data receiving point |
|
| 3 |
source address |
6 |
MAC address of the data transmission point |
|
| 4 |
Type / Length |
2 |
Ethernet data take care of the exact length of the data |
Range from 0-1500 |
| 5 |
data |
46-1500 |
Data information |
Need to fill when the data is less than 46 bytes |
| 6 |
Frame check sequence |
4 |
Check code |
Used to verify data at the receiving end |
6. Application based on vehicle Ethernet
Automobile manufacturers have begun to attach importance to in-vehicle Ethernet application technology, and many mainstream automobile manufacturers have joined in the formulation and promotion of in-vehicle Ethernet related standards.
BMW X5 uses vehicle-mounted Ethernet technology that can achieve a transmission rate of 100 Mbit / s in the path connecting the peripheral monitoring camera module and the ECU to transmit images, and uses Ethernet in the transmission path of the information communication system connecting the vehicle-mounted information terminal and the central gateway.
Toyota has developed automotive LAN interface specifications based on Ethernet, and has cooperated with Renesas Electronics and Broadcom to begin activities to achieve international standardization.
In Ethernet data transmission technology, a pair of UTP (unshielded twisted pair) can be used to achieve a transmission rate of 100 Mbit / s. The physical layer uses the NXP TJA1100 as the interface between the analog transmission medium and the data MAC controller to meet the automotive industry EMC requirements and can support cable lengths up to 25M. The 2014 and 2015 BMW X5, 2015 Jaguar XJ and 2015 Volkswagen Passat has useful vehicle Ethernet technology.
The application of in-vehicle Ethernet in advanced driver assistance systems effectively solves the need for information transmission and integration. The latest ADAS systems usually use high-speed Ethernet to build data links, connecting multiple high-dynamic-range megapixel cameras.
The communication between in-vehicle equipment and devices mainly uses wired in-vehicle networks. According to the different information transmission, CAN, LIN, MOST, FlexRay, on-board Ethernet and other networks are used. Some devices, because of the relatively moving parts to be communicated, cannot be directly connected by wires, or will be inconvenient, they will use wireless transmission, such as tire pressure monitoring system.
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