[Technology Report]
Software And Hardware Standards Help, But In-Vehicle Network Growth Will Be Conservative
CAN networks and OSEK/VDX-compatible operating systems will drive tomorrow's vehicles.
Vehicles will be home for some of the most diverse network and multiprocessing technology over the next five years. Standards will help improve acceptance and reduce costs, but the competitive nature of the industry limits the scope of hardware and software standards. Interchangeable computer-related components will probably remain manufacturer-specific for some time, with the exception of consumer-replaceable multimedia and communication components.
Leading the standardization charge for networks in automotive environments is the Controller Area Network (CAN) with OSEK/VDX (German for Offene Systeme und deren Schnittstellen für die Elektronik im Kraftfahrzeug/Vehicle Distributed eXecutive) providing a standard for real-time operating systems for the many embedded processors found in automotive networks. Both actually are well established standards, but their use is only in the beginning stages. They can be found on today's luxury cars and trucks, where computer-controlled and networked services are common.
CAN isn't the only kind of network found in automobiles. At the low end, the Local Interconnect Network (LIN) is being employed. A variety of multimedia networks are undergoing evaluation too, including a modified version of the IEEE-1394 standard to allow operation in a more hostile environment, the automobile.
In addition, software standards are becoming important in vehicle software development because of the need for high reliability and efficient development. OSEK/VDX isn't the only software initiative. Motor Industry Software Reliability Association (MISRA) C and Embedded C++ are standards designed to improve overall application development. C and C++ are languages of choice, with the assembler still filling in for low-end microcontroller development. Some of these standards target the automotive industry, but all are applicable to embedded application development.
All vehicles will eventually be extensively networked, making them more complex than any home and most office networks. The number of embedded networked processors also will be very high in vehicles. Dozens of processors will handle everything from car locks to braking control.
Automotive networks and software are undergoing customization for their target environment, yet the employment of this technology is for more than vehicle command and control. Today, CAN networks appear in various applications, from robotics to medical equipment. CAN's flexibility, low cost, and standardization make it an ideal alternative to more expensive networks, such as Ethernet.
Europe leads in the incorporation of standards-based operating systems and network protocols in their luxury models with about a two-year lead over American and Japanese models. This is due more to the momentum of existing technology than technical expertise.
Many American automobiles are networked using the 41.6-kbit/s J1850 standard. Unfortunately, J1850 has turned into three relatively unique implementations. J1850-based component use is consistent within each automobile vendor's product line, but not between vendors.
The American migration to CAN and the inclusion of other network technologies like LIN is expected to proceed in an incremental fashion with CAN, and sometimes LIN, replacing J1850.
Automotive Networks Even today, automobile networks are hierarchical in nature with multiple segments. Partitioning is done for a variety of reasons, from network segment bandwidth considerations to reliability and firewall considerations.
Automotive systems can operate independently if network or gateways fail. This lets vehicles continue operation in a degraded capacity when failures occur.
Redundant networks aren't presently employed, but this may change over the next 10 years as X-by-wire comes into play. The term X-by-wire covers network control of critical systems, like steering and braking. Airplanes have employed X-by-wire for years, with redundant systems keeping planes flying at full capability even when some faults happen. This level of reliability is necessary before consumers will consider buying high-tech automobiles.
How might networks be distributed throughout an automobile? A typical automobile in 2005 should have half a dozen different kinds of networks and three times that many network segments (Fig. 1). This is a remarkable level of complexity, but it's one that will be designed for low cost and high reliability. In general, automotive networks can be grouped by purpose, such as control, X-by-wire, and multimedia.
A Harbinger Of Things To Come The new Mercedes Benz C and S Class models offer a look at things to come. Mercedes Benz's in-vehicle CAN network supports features like Automatic Slip Control and Electronic Stability Program. These communicate with a number of different subsystems including braking, the differentials, and the engine. A fiber-optic network is used for cell-phone and audio features.
Mercedes Benz is moving toward X-by-wire technology with its throttle boost and brake assist. The throttle boost augments the acceleration when the gas pedal is depressed. On the other hand, the brake assist increases the braking pressure based on the acceleration of the brake pedal. A quick depression of the brake pedal, to avoid an accident for instance, causes a power boost to the brakes. So, the car stops more quickly.
The J1850 standard with its various implementations is one of the most common automotive control networks in the U.S. It's shown in relationship to other networks like CAN and LIN in the table.
CAN is a midrange protocol definition that can be utilized with many different physical layers. CAN and LIN products are available from companies such as NEC, Microchip, Motorola Semiconductor, Delphi Automotive, and Philips Semiconductors. Microchip's PIC18Cx58 CAN controller and PIC16C43x LIN controllers are examples of integrated transceivers and microcontrollers designed to lower costs.
CAN, a Carrier-Sense-Multiple Access by Collision Detection using Arbitration (CSMA/CD-A) protocol, can operate at speeds up to 1 Mbit/s when the network is less than 30 meters long. By reducing the speed to 10 kbits/s, the maximum distance grows to 5000 meters. Regardless, CAN has a multimaster architecture with prioritized messages of 8 bytes or less, plus a 15-bit cyclical redundancy check (CRC).
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