Electronic Design

The iDrive: Driving A Faster Bus

There is a lot more to BMW's research and development effort than iDrive. For example, take FlexRay, the automotive network communications system. BMW and Daimler-Chrysler, along with Philips and Motorola (now Freescale Semiconductor), formed the FlexRay Consortium back in 2000. Since then, Ford, General Motors, and many other European and Asian big-name automakers and tier-one suppliers have joined. FlexRay is competing against the Time Triggered Protocol (TTP) Forum to become the industry-standard protocol that someday will enable by-wire applications to replace mechanical systems.

FlexRay aims to increase bandwidth in vehicular networks that link up to 70 electronic control units (ECUs) and to provide deterministic support for time-sensitive applications, notes Ross McOuat, European operations manager for control devices at Freescale Semiconductor and the firm's program sponsor for FlexRay. Bandwidth-wise, FlexRay jumps from CAN's 1 Mbit/s or less to two parallel channels at 10 Mbits/s each over twisted pair—the same low-cost medium that CAN employs—versus optical fiber. FlexRay's use of parallel channels creates redundancy, which, like deterministic behavior, is a sine qua non for by-wire designs: It's one thing to experience a delay when tuning in one's favorite hip-hop station but quite another if a vehicle's steering or braking systems are slow in responding.

"But FlexRay is in a very early stage of adoption," cautions McOuat, amid current skepticism surrounding X-by-wire. (Mercedes-Benz recently recalled 680,000 vehicles equipped with a brake-by-wire system.) McOuat touts the technology's performance in real-time data-transfer environments.

To bootstrap FlexRay development, Decomsys offers Node, a prototyping platform featuring an ARM9-based Altera Excalibur EPXA4 programmable-logic device. Automotive network software developer Vector Informatik GmbH is launching FlexCard, a two-channel FlexRay interface card for simulation and analysis. It interfaces with a FlexRay bus via RS485 or Philips' TJA1080 bus driver physical-layer device, and it supports FlexRay controller implementation V6.2. Also in the FlexRay tools market, dSpace Inc. says its Real-Time Interface (RTI) FlexRay Blockset provides the RTI extensions needed for laboratory-based or in-vehicle application development.

FlexRay supports synchronous and asynchronous transmission or a combination of the two. According to McOuat, time-triggered communication is possible in synchronous mode, with minimum message latency and jitter guaranteed. In the asynchronous mode, which is based on byteflight protocol, each node can use the full system bandwidth for event-driven assignments.

BMW was a prominent member of the team that developed byteflight. The company uses the protocol in 7 Series vehicles as part of a passive safety system called the Intelligent Safety Integration System, or ISIS, which links 13 ECUs in a fiber network.

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