A quiet revolution is sweeping through automotive in-vehicle, vehicle-to-vehicle, and vehicleto- infrastructure communications and networking. Companies as well as standards organizations continue to successfully tackle major design challenges, such as the adoption of hardware and software approaches to meet demanding bandwidth, fault-tolerance, determinism, and reliability requirements.
In fact, there’s marked improvement among a number of communications and control protocols, both hardware and software. These include FlexRay, Controller Area Network (CAN), the Japan Automotive Software Program ARchitecture (JASPAR), the Local Interconnect Network (LIN), the Society of Automotive Engineers (SAE) J1850, the AUTomotive Open System ARchitecture (AUTOSAR), the Media-Oriented Systems Transport (MOST), and the FireWire (1394) standard. The MOST protocol is finding its way into more automotive infotainment systems, mainly in European cars (see “The Line Between Telematics And Infotainment Blurs Even Further”). It isn’t on the road yet, but Toyota is using a 25-Mbyte/s version of MOST in its Prius. Release of the MOST specification Rev. 3 for 150-Mbit/s networks is expected soon.
As for body, powertrain, chassis, and other controls, no one protocol and architecture can be considered as a “one size fits all” solution. Quite often, combinations and refinements of these approaches prove valuable in providing flexibility and meeting automotive control and communications needs. For example, JASPAR was recently adopted for the upcoming version of FlexRay targeting next-generation in-car networks. The FlexRay Consortium will incorporate a JASPAR technical proposal in the main modification points of FlexRay’s Protocol Specification V3.0 and the Physical Layer Specification V3.0, to be released in the 2009/2010 timeframe.
FlexRay continues to serve as a major backbone for automotive applications (Fig. 1). German and Japanese OEMs decided to adopt FlexRay in their car networks. In fact, the first vehicles to commercially use the FlexRay protocol are BMW’s flagship X5 sport utility vehicles (SUVs) and its 7 series of cars.
FlexRay defines a dual-channel 10-Mbit/s data structure. Each channel can be used to implement a redundancy mechanism in a standalone manner, for an aggregate data rate of 20 Mbits/s.
Core members of the FlexRay Consortium (BMW, General Motors, Volkswagen, Daimler-Chrysler, Bosch, Freescale Semiconductor, and NXP Semiconductor) expect FlexRay to become the standard for advanced powertrain, chassis, and x-by-wire automotive systems, even though it presently costs more than the widely used 1-Mbit/s CAN protocol. Most members feel FlexRay will integrate with other protocols rather than replace them.
“FlexRay was originally designed for fault tolerance and redundancy. Now it is also being used for bandwidth where greater bandwidth can be achieved with other networks like CAN,” says Jens Eltze, principal technical application engineer for NEC Electronics America’s Automotive Strategic Business Unit.
“There’s a natural reluctance on the part of some automakers to adopt a standard based on a new technology like FlexRay, FireWire, etc. They don’t want to take a chance that it may or may not succeed until others join in,” says Dave Stone, marketing manager for NEC Electronics America’s Automotive Strategic Business Unit.
BRIDGING THE GAP
Some IC chip manufacturers are trying to narrow the costdifferential margin between FlexRay and CAN. Austria Microsystems (AMS) and TTTech Automotive are joining forces to develop lower-cost FlexRay transceiver devices. They plan to intensify their R&D efforts to create FlexRay automotive networking nodes.
The goal of the joint effort is to improve the reliability of invehicle data communication and reduce costs. For instance, optimized FlexRay topologies could integrate a larger number of nodes. In addition, the companies designed a bit re-shaper circuit that will let automotive OEMs and tier 1 suppliers reduce cabling costs by using less costly wiring types. Both companies also plan to collaborate in creating test processes for the FlexRay chips.
“The price of FlexRay chips will come down to mitigate the large cost differential between FlexRay and CAN implementations,” says Toni Versluij, senior director and general manager in the Business Line Automotive Safety & Comfort Unit at NXP Semiconductors.
NXP introduced the first FlexRay transceiver IC, the TJA 1080A, in 2006. The TJA1081 and TFA1082 node transceivers soon followed (Fig. 2). There’s also the TJA1085 active star coupler. NXP has shipped 1 million FlexRay transceivers that comply with the physical layer. The company has been a supplier of FlexRay chips, as well as CAN and LIN, for over a decade.
“CAN will be the choice for automotive networking nodes over the next decade,” says Versluij (Fig. 3). He points out that although FlexRay with its dual channels was originally designed for x-by-wire applications needing redundancy, the vast majority of automotive applications uses a single-channel topology that CAN is able to handle. CAN works with the SAE’s J1850 bus, which is widely used for on-board diagnostics (OBD) II.
Versluij also notes that at the component level, FlexRay costs more than CAN to implement. Not so at the systems level, though. Serg Leef, general manager of Mentor Graphics’ Systems Engineering Division, concurs.
“CAN has bandwidth and reliability limitations. Users tend to compensate for this by designing networks that use only a limited portion of total bandwidth to increase the likelihood that messages will arrive in a sufficiently timely manner, which diminishes CAN’s price/performance ratio,” says Leef.
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