Enigmatos Blog

FlexRay Protocol Overview

FlexRay is an automotive network communications protocol, it was developed in conjunction with automobile manufacturers and leading suppliers who together formed the FlexRay Consortium to govern on-board automotive computing. The FlexRay consortium disbanded in 2009.

Advantages & Disadvantages

FlexRay is much faster and more reliable than existing CAN systems, it is also a deterministic system, which gives high reliability of communications. FlexRay can handle any type of network configuration, it is 10 times faster than CAN, however it is more expensive, hence it is highly suited to high-performance power train, drive-by-wire, active suspension and adaptive cruise control systems. FlexRay can be used as the bus protocol for highly advanced vehicle technologies, requiring absolute reliability, such as drive-by-wire, steer-by-wire and brake-by-wire where the bus and all its components must last the life of the vehicle without even momentary failure. FlexRay has been used by the following manufacturers in their latest top of the range models: Audi, Bentley, BMW, Lamborghini, Mercedes, Rolls Royce, Land Rover, Volvo.

How Does It Work?

FlexRay uses ordinary unshielded wires as a twisted pair for communication and is suitable for all bus configuration types, including multi-drop bus, star network and hybrid network.

The FlexRay Protocol

 The FlexRay protocol is a unique time-triggered protocol that provides options for deterministic data that arrives in a predictable time frame (down to a microsecond). CAN uses an arbitration scheme where nodes will yield to other nodes if they see a message with higher priority being sent on a bus. FlexRay prioritizes the messages.FlexRay manages multiple nodes with a Time Division Multiple Access or TDMA scheme. Every FlexRay node is synchronized to the same clock, and each node waits for its turn to write on the bus.  Because the timing is consistent in a TDMA scheme, FlexRay is able to guarantee determinism or the consistency of data delivery to nodes on the network.  Low priority data simply has to “wait in a queue”. This provides many advantages for systems that depend on up-to-date data between nodes.

Summary

A FlexRay signal can carry up to 30 times the data of a CAN message and has 3 CRC checks, this gives FlexRay many advantages over CAN bus systems which use a more “flexible” message timing system with less data and less tightly controlled messages & less message verification. Since FlexRay by definition was designed and produced specifically for use in automotive networks, it is highly unlikely to find it in any applications other than automotive. Indeed, no other industries to date have adopted the FlexRay protocol.

The Future

It can be seen that FlexRay has not to date been adopted by mass production vehicle manufacturers and has been used exclusively by high end premium vehicle manufacturers. However, we expect that Ethernet systems will be used by vehicle manufacturers in the future rather than FlexRay.  

Ralph Diamond, Director of Engineering, Enigmatos, March 2018
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