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      01-26-2007, 01:32 PM   #9
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Originally Posted by m_bazeepaymon View Post
wat is flex ray
What is FlexRay?

For these automotive applications to become commonplace, a number of protocol requirements must exist. Enter FlexRay. FlexRay is a communication system developed by a consortium founded in 2000 by BMW, DaimlerChrysler, Motorola, and Philips Semiconductors. In 2001, Robert Bosch GmbH and General Motors joined the consortium. So did Ford Motor Company this past June. The consortium members realized that despite the numerous automotive communications protocols out on the market—most from Europe, most in or just out of development—none would fulfill future automotive control requirements. Even the computer communications protocols don't suffice. "None of them are automotive qualified," explains Andreas Both, business and technology manager overseeing FlexRay for the Semiconductor Products Sector of Motorola (Munich, Germany). That is, they are not qualified for automotive operating temperatures and electromagnetic compatibility requirements. (Remember hearing spark plugs fire through your aftermarket AM radio?)

FlexRay is an open, common, scalable electronic architecture for automotive applications. It can operate in single- or dual-channel mode, providing redundancy where needed. It allows both synchronous and asynchronous data transmissions. With the former, other nodes on the network receive time-triggered messages in a predefined latency time. With the latter, messages get to their destinations quickly or slowly, depending on their priority. Currently, FlexRay can handle communications at 10 Mbps—the speed of your typical low-end home-computing local area network. Motorola's Both is quick to add that this standard doesn't mean that 10 Mbps is enough forevermore. Instead, it is fast enough for the foreseeable future, given the applications automakers have envisioned thus far.

Last, FlexRay's clock synchronization mechanism aptly handles cheap clock oscillators, namely those made out of quartz. And that synchronization, as with all of FlexRay, is fault tolerant. For example, FlexRay automatically and digitally compensates for the differences in the variety of quartz clocks running on the network, as well as in their slight changes in clock frequencies. This clock synchronization is a distributed mechanism; there's no master timekeeper here. So if one node fails or for some reason is taken off the network, the other nodes will continue to operate in synchrony.

(Insofar as the fault tolerance of motors and sensors, the normal rules of reliable systems design applies. For example, in a steer-by-wire system, the sensor system in the steering wheel will be a redundant array, with two or three sensors providing the same signal. A judging algorithm in the electronics will then determine the validity of the signals; that is, it will determine whether all three sensors are providing the same information, or at least two of the three.)

IMHO: best, clearest and most detailed info here:

2007 BMW X5 intros high-speed communication chip based on Flexray tech
Wolfgang Gruener

August 9, 2006 15:51

Munich (Germany) - BMW today announced a new version of its X5 flagship SUV. It's larger, stronger and faster and probably better and more expensive than its predecessor, but what makes this new model especially interesting form a technological view is the presence of a Flexray chip.

Developed in a consortium that includes BMW, Bosch, DaimlerChrysler, Freescale, General Motors, Philips and Volkswagen, Flexray is a protocol that delivers about 10 Mbit/s bandwidth for communication between active and passive safety systems, collision avoidance systems, powertrain management systems and driver assistance systems. Flexray is about 20 times faster than comparable and current in-car communication systems, according to Freescale.

According to the Flexray consortium, the technology is expected to be used in time- and event-triggered communication schemes, support of fault-tolerant systems and offer a high error detection and error diagnosis capability, a dedicated automotive electrical physical layer with sophisticated powerdown and wake up mechanisms, extendability and scalability for upgrades and support for different network topologies.
Freescale is currently the only manufacturer that has announced Flexray processors.

Why the Switch?

The next-generation BMW X5 is said to implement the first application of Flexray in the automotive world, using the relatively new networking protocol for its electronically controlled dampers. This will come approximately two years before the manufacturer rolls out its first platform that uses Flexray as the main vehicle communications backbone. The CAN-C systems currently in place are limited to 500 kbs, which many manufacturers are finding isn't fast enough. Even more problematic, CAN isn't deterministic; that is, it cannot be assured that a message will be successfully transmitted at a particular point in time. There are ways of asserting priority on the network, but this involves playing favorites - not acceptable when it comes to deciding whether the braking or steering is more important, and while those two were arguing, your electromechanical valve system just crashed. Flexray solves both problems by increasing the data rate, and implements a low-cost means of establishing a network clock so that each module is given a discrete slice of time in which it can do its thing. There's a decent introduction to it here for those looking to learn more. Expect to hear a lot more about this in the next few years. In the meantime, those of us heavily invested in CAN development tools will hopefully get our money's worth.


Hope this answers your question.