Put the Right Bus in Your Car

The amazing array of features available in today’s cars has spawned new in-vehicle bus standards.

by Karen Parnell tems, have spurred annual growth rates as bandwidth and speed restrictions make it Automotive Product Manager high as 16%, according to the Institute of difficult for these serial, event-driven buses Xilinx, Inc. Electrical and Electronics Engineers to handle newer real-time applications. [email protected] (IEEE). The IEEE forecasts that electron- A number of new bus standards have ics will account for 25% of the cost of a emerged featuring time-triggered protocols The next few years will be a rocky road for mid-size car by 2005. and optical data buses. These in-car bus net- automobile electronics designers. No sin- One high-growth area is telematics sys- works can be divided into four categories: gle in-car data bus can adequately handle tems – the convergence of mobile telecom- • Body control – dashboard/instrument the entertainment, safety, and intelligent- munications and information processing panel clusters, mirrors, seat belts, door control requirements of the cars that will in cars. Significantly, telematics applica- locks, and passive airbags roll off assembly lines in North America, tions exhibit market characteristics similar Europe, and Asia. to those of consumer products: short time • Entertainment and driver-information Choosing the right data bus can lead to to market, short time in market, and systems – radios, Web browsers, a competitive advantage, but the selection changing standards and protocols. These CD/DVD players, telematics, and is increasingly difficult, as carmakers market characteristics are just the opposite infotainment systems around the globe adopt different solutions. of the relatively long design cycles of tradi- • Under the hood – antilock brakes, tional in-car electronics, which are often emission control, power train, and Electronics Drives Innovation dictated by safety and tooling-cost consid- transmission systems In-car electronics have grown tremendous- erations. ly in recent years. Traditional body-control Traditional systems such as CAN (con- • Advanced safety systems – brake-by- and engine-management functions, plus troller area network) and J1850 have been wire, steer-by-wire, and driver assis- new driver-assistance and telematics sys- used in body control for many years. But tance systems (active safety).

00 Xcell Journal Winter 2004 Figure 1 shows the relative speeds of the LIN network with higher-level networks Media Oriented System Transport various bus systems, which range from such as a CAN bus, extending the benefits MOST networks connect multiple devices, kilobits per second to gigabits per second. of networking all the way to the individual including car navigation, digital radios, dis- sensors and actuators. plays, cellular phones, and CD/DVDs. “Under-the-Hood” Buses MOST technology is optimized for use Two networks found under the hood serve Entertainment and with plastic optical fiber. It supports data functions ranging from seat adjustment to Driver Information Systems rates as high as 24.8 Mbps and is highly antilock brakes. Car infotainment and telematics devices, reliable and scalable at the device level. especially car navigation systems, require MOST offers full support for real-time Controller Area Network highly functional operating systems and audio and compressed video. It is vigorous- One of the first and most enduring control connectivity. Until now, both open-stan- ly supported by German automakers and networks, the CAN bus, is the most widely dard and proprietary standalone buses have suppliers. The MOST bus is endorsed by used, with more than 100 mil- BMW, DaimlerChrysler, lion nodes installed worldwide. Harman/Becker, and OASIS A typical vehicle integrates 1394b 3.2 Gbps High Speed Silicon Systems. A recent two or three CAN buses oper- notable example of a MOST ating at different speeds. A low- IDB-1394 implementation is its use by speed CAN bus runs at less 1394a 400 Mbps Harman/Becker in the latest than 125 Kbps and manages BMW 7 series. body-control electronics, such MOST 45 Mbps as seat and window movement TTP 25 Mbps Intelligent Transport controls and other simple user D2B System Data Bus interfaces. A high-speed (up to FlexRay/byteflight 10 Mbps The IDB Forum manages the 1 Mbps) CAN bus runs real- IDB-C and IDB-1394 buses TTCAN time critical functions such as 1 Mbps and standard interfaces for GM-LAN High Speed engine management, antilock OEMs that develop aftermar- IDB-C CAN 1 Mbps Ð 50 Kbps brakes, and cruise control. ket and portable devices. CAN protocols are becom- Safe-by-Wire 150 Kbps Based on the CAN bus, IDB- GM-LAN Low/Mid Speed ing standard for under-the- LIN <20 Kbps Low Speed C is geared toward devices hood connectivity in cars, with data rates of 250 Kbps. trucks, and off-road vehicles. IDB-1394 (based on the One outstanding feature of the Figure 1 – In-car network data-transfer speeds IEEE-1394 FireWire™ stan- CAN protocol is its high trans- dard) is designed for high- mission reliability. coexisted independently and peacefully. speed multimedia applications. IDB-1394 But because of the pressures of conver- is a 400 Mbps network using fiber-optic Local Interconnect Network gence, future systems will require integrat- technology. Applications include DVD and The local interconnect network (LIN) was ed electronic subsystems. CD changers, displays, and audio/video developed to supplement the CAN bus in By relying on open industry standards, systems. applications where cost is critical and data all key players – from manufacturers to IDB-1394 also allows 1394-portable transfer rates are low. The LIN bus is an service centers to retailers – can focus on consumer electronic devices to connect and inexpensive serial bus used for distributed delivering core expertise to the customer. interoperate with an in-vehicle network. body control electronic systems. It enables Open standards will save the duplication Zayante Inc., for example, supplies 1394 effective communication for smart sensors of time and effort it would take to devel- physical layer devices for the consumer and actuators where the bandwidth and op separate, incompatible designs for spe- market. A recent joint demonstration with versatility of the CAN bus are not required. cific vehicles or proprietary computing the Ford Motor Company included plug- Typical applications are door control (win- platforms. and-play connections of a digital video dows, door locks, and mirrors), seats, cli- Several organizations and consortia are camera and a Sony PlayStation™ 2 game mate regulation, lighting, and rain sensors. leading standardization efforts, including console, as well as two video displays and a The LIN bus is a UART-based, single- the MOST (Media Oriented System DVD player. master, multiple-slave networking architec- Transport) Cooperation, the IDB ture originally developed for automotive (Intelligent Transport System Data Bus) Digital Data Bus sensor and actuator networking applica- Forum, and the Bluetooth™ Special The Digital Data Bus (D2B) is a network- tions. The LIN master node connects the Interest Group (SIG). ing protocol for multimedia data commu-

Winter 2004 Xcell Journal 00 nication that integrates digital audio, that for consumer products or mobile FlexRay standard for next-generation video, and other high-data-rate synchro- phones, so silicon manufacturers must applications. nous or asynchronous signals. It can run as address this mismatch between support The FlexRay system is more than a fast as 11.2 Mbps and be built around and service timescales. On the other hand, communications protocol. It also includes either SmartWire™ unshielded twisted Chrysler showed Bluetooth connectivity in a specially designed high-speed transceiver pair cable or a single optical fiber. its vehicles at Convergence 2002. and the definition of hardware and soft- This communication network is being Some feel Bluetooth technology may be ware interfaces between various compo- driven by C&C Electronics in the UK and overkill in the car environment, however. nents of a FlexRay “node.” The FlexRay has industry acceptance from Jaguar and So, an emerging standard for low data rate protocol defines the format and function of Mercedes-Benz. The integrated multime- wireless data transfer and control has the communication process within a net- dia communication systems deployed in entered the scene. The ZigBee™ wireless worked automotive system. It is designed the Jaguar X-Type, S-Type, and new XJ networking solution is a low-data-rate (868 to complement CAN, LIN, and MOST Saloon, for example, use D2B. MHz to 2.4 GHz), low-power, low-cost networks. The D2B optical multimedia system is system pioneered by Philips. The ZigBee As a scalable system, FlexRay technolo- designed to evolve in line with new tech- range is up to 75 meters and is equally at gy supports both synchronous and asyn- nologies while remaining backwards com- home in industrial control, home automa- chronous data transmission. The patible. D2B optical is based on an open tion, consumer, and possibly automotive synchronous data transmission enables architecture that simplifies expansion, applications. time-triggered communication to meet the because changes to the cable harness are requirement of dependable systems. not required when adding a new device or Advanced Safety Systems FlexRay’s synchronous data transmission is function to the optical ring. The bus uses Safety equipment has evolved from the deterministic, with guaranteed minimum just one polymer optical fiber to handle physical to the electronic domain, starting message latency and message jitter. It sup- the in-car multimedia data and control with advancements in tire and braking ports redundancy and fault-tolerant dis- information. This gives better reliability, technology, through side impact protection tributed clock synchronization to keep the fewer external components and connec- and airbags, and on to today’s driver-assis- schedule of all network nodes within a tors, and a significant reduction in overall tance systems. tight, predefined, precision window. system weight. The latest vehicles are electronics-rich The asynchronous transmission, based on and sensor-based to continuously evaluate the fundamentals of the byteflight™ proto- Bluetooth and ZigBee the surroundings, display relevant informa- col, allows each node to use the full band- Bluetooth wireless technology is a low-cost, tion to the driver, and, in some instances, width for event-driven communications. low-power, short-range radio protocol for even take control of the vehicle. mobile devices and WAN/LAN access Advanced safety systems include by- Time-Triggered Protocol points. Its specification describes how wire (for example, drive-by-wire and brake- Designed for fault-tolerant, real-time dis- mobile phones, computers, and PDAs can by-wire), which will replace traditional tributed systems, the time-triggered proto- easily interconnect with each other, with hydraulic and mechanical linkages with col (TTP) ensures that there is no single home and business phones, and with com- safer, lighter electronic systems. point of failure. puters. Other examples of advanced, real-time TTP is a mature, low-cost solution that The Bluetooth SIG includes such mem- safety systems include distance control, can handle safety-critical applications. bers as AMIC, BMW, DaimlerChrysler, self-adjusting and sensing airbag systems, Second-generation silicon supporting com- Ford, General Motors, Toyota, and radar parking, reversing aids, and back munication speeds as high as 25 Mbps is Volkswagen. An example of Bluetooth guide monitors (cameras set in the car’s available today. The TTA Group, the gov- deployment in cars is Johnson Controls’ bumpers to aid parking). erning body for TTP, includes Audi, SA, BlueConnect™ technology, a hands-free Renault, NEC, TTChip, Delphi, and system that allows drivers to keep their FlexRay Visteon among its members. hands on the wheel while staying connect- The FlexRay™ network communication ed through a Bluetooth-enabled cellular system is aimed at the next generation of by- Time-Triggered CAN phone. wire automotive applications. These applica- The time-triggered CAN (TTCAN) stan- There is, however, some concern about tions demand high-speed buses that are dard is an extension of the CAN protocol. long-term support of Bluetooth devices. deterministic, fault-tolerant, and capable of It adds a session layer on top of the existing The problem centers on how the electro- supporting distributed control systems. data link layer and physical layers to ensure magnetically noisy in-car environment will BMW, DaimlerChrysler, Philips that all transmission deadlines are met, affect Bluetooth operation. The lifecycle of Semiconductors, Motorola, and the newest even at peak bus loads. The protocol imple- cars and other vehicles is much longer than member, Bosch, are developing the ments a hybrid, time-triggered, TDMA

00 Xcell Journal Winter 2004 Figure 2 – In-car multimedia functions embedded in an FPGA

(time-division multiplexed access) schedule design process – and even in production. The Memec core is designed to provide that also accommodates event-triggered The reconfigurable system concept sup- a bus bit rate of up to 1 Mbps, with a min- communications. Some of the intended ports try-outs of different standards and imum core clock frequency of 8 MHz. It TTCAN uses include engine management protocols. Programmable logic devices can provide an interface between the mes- systems and transmission and chassis con- (PLDs) in the form of FPGAs and CPLDs sage filter, the message priority mechanism, trols, with scope for by-wire applications. enable modification during all phases of and various system functions such as sen- design – from prototype through pre-pro- sor/activator controls. The Programmable Logic Solution duction and into production. Alternatively, the Memec CAN bus can As we have seen from the proliferating num- PLDs can also alleviate over-stocking be embedded into a system application ber of in-car bus standards, the next few years and inventory issues, because generic interfacing with the microprocessor and will become a minefield for automotive elec- FPGAs can be used across many projects various peripheral functions. Another tronics designers. Choosing the right data and are not application-specific. Once the example is Intelliga’s iLIN™ core, which is bus will be crucial to success – now measured programmable logic-based unit is on the supplied as a LIN bus controller IP core. It not simply during integration and testing of road, it can even be reconfigured remotely uses a synchronous 8-bit general-purpose units for production, but long after the car via a wireless communication link to allow microcontroller interface with minimal has rolled off the assembly line. for system upgrades or extra functions. buffering to transport message data. In The problem is amplified for Tier 1 addition, the reference design includes a suppliers and aftermarket companies that Drop-In IP Cores single slave message response filter and a supply units to many OEMs, because The reconfigurable hardware platform can software interface that allows the connect- these customers are likely to opt for differ- be brought to market quickly by utilizing ed microcontroller to perform address fil- ent data buses and protocols. The industry drop-in intellectual property (IP) core tration. has seen a huge shift away from designing blocks. Memec Design, for example, This emerging LIN body control proto- a different unit for every OEM – indeed recently announced the availability of a col can be easily tried and tested using the for every car model. Taking its place is a cost-optimized CAN core interface that Intelliga iDEV prototyping board, which design philosophy that emphasizes recon- includes the complete data link layer, can demonstrate not only LIN but also figurable platforms. including the framer, transmit-and-receive CAN and TTCAN buses – all implement- Design platforms that are cleverly parti- control, error core design, and flexible ed in a Xilinx Spartan™-IIE FPGA. tioned between software and reprogram- interface. Bit rate and sub-bit segments can Figure 2 shows a generic in-car multi- mable hardware let manufacturers change be configured to meet the timing specifica- media system design with a CAN core sup- system buses and interfaces late in the tion of the connected CAN bus. plying communications for a PCMCIA

Winter 2004 Xcell Journal 00 Figure 3 – In-car complementary networks interface, PCI bridging, an IDE interface, a FlexRay bus (or other real-time safety Website resources and other functions. One printed circuit bus) to handle the high-speed, real-time board can be used for many customers with data required by advanced safety systems. CAN www.can.bosch.com customization in the FPGA instead of the board. The model can be extended to Conclusion GM LAN www.gmtcny.com/lan.htm include modification or upgrades in the The delicate engineering balance between field via wireless connection to reconfigure cost, reliability, and performance has creat- MOST www.mostnet.de the FPGA in-system. ed a variety of emerging in-car bus systems that will complicate design decisions for TTTech (TTP) www.ttagroup.org, www.ttchip.com Bus Coexistence years to come. Therefore, automotive FlexRay www.flexray.com Several in-car bus networks can coexist to OEMs are backing more than one standard deliver the right combination of data rates, due to uncertainties over which one will D2B www.candc.co.uk robustness, and cost. eventually prevail. Figure 3 shows the LIN bus handling There is an elegant solution to this LIN www.lin-subbus.org low-cost, low-speed connections between dilemma. Reconfigurable platforms based the motors for the mirrors, roof, windows, on Xilinx programmable logic and IP cores Intelliga (LIN) www.intelliga.co.uk and so forth. A CAN bus handles data are the best way out of this design predica- communication and control between the ment. Without sacrificing performance or Bluetooth www.bluetooth.com instrument cluster, body controllers, door cost advantages, reconfigurable hardware IDB locks, and climate control. Finally, the and software systems from Xilinx allow www.idbforum.org high-speed MOST optical bus connects manufacturers to quickly accommodate ZigBee www.zigbee.org the entertainment, navigation, and com- changing standards and protocols late in munication devices. the design process, in production, and even Xilinx Automotive www.xilinx.com/automotive/ This model can be extended to include on the road.

00 Xcell Journal Winter 2004