Automotive Ethernet Challenges CAN Bus

With the development of intelligent vehicles, automotive Ethernet has become an indispensable part of advanced automotive electronic architecture. In the central node, automotive Ethernet has occupied an absolute dominant position, but in the edge node, buses such as CAN, CAN-FD and FlexRay still occupy a dominant position, especially CAN. This makes it difficult for automotive electronic architecture to reach the true Zonal level and can only stay at the domain controller level. Zonal architecture is a must for software-defined cars or service-oriented architecture.

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The typical Zonal architecture is the concept of a server. Through the vehicle Ethernet backbone network, the supercomputing core (i.e., server or high-performance computing, i.e., HPC) handles the computing needs of all nodes. The car becomes similar to the PC architecture, with complete separation of software and hardware, unified hardware, and most of the work is done by software, relying on operating systems such as LINUX and adaptive AUTOSAR, and the hardware is completely transparent to programmers.

There are two major areas at present, one is the sensor field, and the other is the actuator field. In-vehicle Ethernet is urgently needed to replace the traditional CAN bus. The sensor field mainly includes ultrasonic sensors, millimeter-wave radar sensors, microphones for emergency calls, and finally sensors for position, speed, pressure, temperature, etc. for power transmission parts. The actuator field mainly includes lights, including headlights, interior lights, and ambient lights; speakers, door speakers, subwoofers, and emergency call speakers; and finally various motors, including windows, various mirrors, pumps, wipers, etc.

In March 2020, IEEE released the 802.3cg standard, namely 10 Mb/s Single Pair (10SPE), which can be used not only in automobiles, but also in industrial control and building automation. There are two standards, one is 10BASE-T1L, which is used for building automation and industrial control, with a maximum distance of 1 km, full-duplex, point-to-point transmission. The other is 10BASE-T1S, which is used in automobiles with a maximum distance of 25 meters. BMW and GM have confirmed that they will replace the CAN bus with 10BASE-T1S in the next generation of cars.

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10BASE-T1S is only a physical layer standard. There are also minor changes in the link layer, but the rest remains unchanged. It is completely transparent to software engineers and they do not need to pay attention to it.

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The above picture shows the electronic architecture of today's most advanced smart car (of course not Tesla). When it comes to the level of advancement of electronic architecture, Mercedes-Benz, BMW and GM are all above Tesla. Tesla is still using old non-car-grade Ethernet.

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In the future automotive electronic architecture, CAN and FlexRay will be replaced by Ethernet, which is 10BASE-T1S.

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At present, advanced domain controllers all use 100BASE-T1 or 1000BASE-T1 automotive Ethernet. This design is performance-oriented. If you want to replace CAN, cost is the most critical. The starting point of 10BASE-T1S is three: low cost, low power consumption, and low electromagnetic radiation. The cost here refers to the overall cost. 10BASE-T1S uses a single pair of unshielded twisted pair cables. Whether it is the connector or the cable cost, it is lower than CAN, and the cable weight is also about 50% lower. In addition, it can be powered by Ethernet, without the need for a separate power supply line.

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10BASE-T1S uses PLCA, Physical Layer Collision Avoidance, to ensure low latency and high reliability. It uses a half-duplex mechanism and cyclic communication scheduled over a BEACON. A BEACON is a marker sent regularly by a coordinate node. After each transmitted BEACON, each station is granted a transmit opportunity (TO).

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10BASE-T1S uses CSMA/CD, Carrier Sense Multiple Access with Collision Detection protocol to transmit data. However, PLCA is added. IEEE found in the test that bandwidth utilization efficiency is the highest after adding PLCA.

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The delay after adding PLCA is also much lower than the traditional CSMA/CD, and will not exceed 1 millisecond. To avoid compatibility issues, PLCA is optional and can be omitted to be compatible with some older MCUs.

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Another feature of 10BASE-T1S is Multidrop mode, which enables multi-node operation without the need for switches or gateways.

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In this network architecture, there is one called the coordinator and the others are called Drop Nodes. Loosely speaking, the coordinator is like the master and the DropNodes are the slaves.

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10BASE-T1S is compatible with the current TC6 or TC14 standards, but PCLA requires 802.3cg.

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In terms of software, the November 2020 version of classic AUTOSAR supports the RMII/MII physical layer, and the November 2021 version supports MACPHY.

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The features of diagnosis, clock synchronization and security are as above, and sleep wake-up and new topology architectures will be added in the future.

Currently, the only common 10BASE-T1S physical layer chip is Microchip's LAN8670/1/2. Texas Instruments and ADI are developing 10BASE-T1L physical layer chips for industrial control and building automation.

LAN8670/1/2 Typical Application Diagram

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LAN8670/1/2 internal framework diagram

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10BASE-T1S cannot shake the position of CAN bus in the automotive field for the time being, but CAN-FD and FlexRay will be strongly challenged by 10BASE-T1S. After taking over CAN-FD and FlexRay, 10BASE-T1S will challenge CAN. At that time, there will only be two buses in the car: Ethernet and LIN.