FlexRay

Computer network protocol

FlexRay is an automotive network communications protocol developed by the FlexRay Consortium to govern on board automotive computing. It is designed to be faster and more reliable than CAN and TTP, but it is also more expensive. The FlexRay consortium disbanded in 2009, but the FlexRay standard is now a set of ISO standards, ISO 17458 1 to 17458 5. FlexRay is a communication bus designed to ensure high data rates, fault tolerance, operating on a time cycle, split into static and dynamic segments for event triggered and time triggered communications.

FlexRay supports data rates up to 10 [[megabit, explicitly supports both star and bus physical topologies, and can have two independent data channels for fault tolerance (communication can continue with reduced bandwidth if one channel is inoperative). The bus operates on a time cycle, divided into two parts: the static segment and the dynamic segment. The static segment is preallocated into slices for individual communication types, providing stronger determinism than its predecessor CAN. The dynamic segment operates more like CAN, with nodes taking control of the bus as available, allowing event triggered behavior.

The first series production vehicle with FlexRay was at the end of 2006 in the BMW X5 (E70), enabling a new and fast adaptive damping system. Full use of FlexRay was introduced in 2008 in the new BMW 7 Series (F01).

The FlexRay system consists of a bus and ECUs (Electronic control unit). Each ECU has an independent clock. The clock drift must be not more than 0.15% from the reference clock, so the difference between the slowest and the fastest clock in the system is no greater than 0.3%. This means that, if ECU s is a sender and ECU r is a receiver, then for every 300 cycles of the sender there will be between 299 and 301 cycles of the receiver. The clocks are resynchronized frequently enough to assure that this causes no problems. The clock is sent in the static segment.

The value of the bit is sampled in the middle of the 8 bit region. The errors are moved to the extreme cycles, and the clock is synchronized frequently enough for the drift to be small. (Drift is smaller than 1 cycle per 300 cycles, and during transmission the clock is synchronized more than once every 300 cycles.)

When developing and/or troubleshooting the FlexRay bus, examination of hardware signals can be very important. Logic analyzers and bus analyzers are tools which collect, analyze, decode, store signals so people can view the high speed waveforms at their leisure.

Ethernet may replace FlexRay for bandwidth intensive, non safety critical applications.