Kicking CAN

May 1, 2008
As automotive electronic systems grow in number, size, and complexity, the need for a faster, more reliable network protocol like FlexRay is increasingly apparent.

Controller Area Network (CAN) networks are likely to be around for many years, but at the high end of the automotive market they are already beginning to lose some ground to FlexRay.

FlexRay is 10 times faster than CAN (10 Mbps versus 1 Mbps); it's time-triggered and deterministic, which makes it predictable, where CAN is not, and because it's predictable, some say it makes application development easier.

FlexRay is a dual-channel protocol that supports redundancy. It's fault-tolerant, and generally considered to be more reliable than CAN. It also works harmoniously with CAN, Local Interconnect Network (LIN), and Media Oriented System Transport (MOST) networks, and the FlexRay Consortium is pursuing alignment of the FlexRay protocol with two other automotive industry standards, AUTOSAR and JasPar.

“The market drivers behind FlexRay include the need to improve fuel economy and reduce CO2 and other harmful emissions, safety, and making cars fun to drive,” said Bjoern Steurich, senior manager for automotive microcontrollers at Infineon Technologies North America. “Vehicles today have as many as 80 ECUs (electronic control units), and networks based on current technology have become overly complex and error-prone. The industry needs a strongly deterministic and fault-tolerant system bus.”

BMW launched the FlexRay era a little more than a year ago with a ride-smoothing application called AdaptiveDrive. The automaker is in the process of implementing FlexRay on several additional models, but the protocol has maintained a low public profile.

Meanwhile, FlexRay is the focus of significant development efforts in labs around the world. “We're experiencing the silence before the storm,” said Rob Hoeben, marketing manager for FlexRay in NXP Semiconductors' automotive business unit. “FlexRay adoption began with German OEMs, but OEMs in Detroit and in Japan are following suit.”

NXP announced in March that its TJA1080A node and star transceiver (Figure 1) passed the FlexRay Physical Layer Conformance Test, the industry standard for FlexRay products. Hoeben said that compliance to the test is an important step in the proliferation of the FlexRay standard because for OEMs it translates into faster development times and fewer production issues. The device, due to ship in the second quarter, provides an interface between the protocol controller and the physical bus in a FlexRay network, monitors internal voltage and temperature, and supports the mode control used in NXP's TJA1055 and TJA1041 CAN transceivers.

Hoeben said BMW is using the TJA1080A predecessor, TJA1080. Among the enhancements in the newer version is full conformance with FlexRay Electrical-Physical Layer V2.1 for improved EMI/EMC performance, improved power-on reset behavior, an upgraded transmitter circuit to reduce emission on bus lines, and an enhanced receiver circuit for higher RF immunity, up to 70 ns minimum bit time.

“We're seeing a trend toward ECUs functioning as central gateways in ABS or suspension applications, with an active star device connecting the MCU by its branches to an ECU containing a node transceiver,” Hoeben noted. “In the future we expect to see more central gateways connected by four or eight branches to more ECUs.”

While the TJA1080A contains a node and an active star in the same device, Hoeben said next-generation devices are likely to contain a node or an active star, in order to give designers more flexibility by enabling more topologies and optimize system deployment costs.

Application developers are benefiting from a growing number of network-specific chips and design tools as they prepare new networks for launch.

NEC Electronics America targets chassis applications, among others, with the 32-bit V850E/PHO3 MCU, which features an embedded FlexRay controller based on E-Ray intellectual property licensed from Robert Bosch GmbH.

Built on NEC Electronics' V850E CPU core, which operates at clock speeds up to 128 MHz and features 1 MB of embedded flash memory, the V850E/PHO3 MCU was one of the first MCUs to pass the FlexRay Conformance Test administered by TÜV Nord Group's Institute for Vehicle Technology and Mobility, the FlexRay Consortium's partner for data link layer conformance testing. The certification is based on 275 tests that verify the functional behavior of an embedded FlexRay communications controller to ensure conformance with the FlexRay v2.1 specification.

“CAN and LIN are well accepted, but there is not much going on with them,” commented Jens Eltze, new business development manager in the Automotive Strategic Business Unit at NEC Electronics America. “FlexRay is the networking technology in the spotlight. It's having big success in Europe, and initial success in Japan and the U.S.”

Eltze said FlexRay holds appeal for developers of steering systems. The V850E/PHO3 has the ability to control one or two 3-phase brushless DC motors simultaneously for applications including electronic power steering, as well as electronic braking, damping and other vehicle-stability control applications.

Eltze said FlexRay holds appeal for developers of steering systems. The V850E/PHO3 has the ability to control one or two 3-phase brushless DC motors simultaneously for applications including electronic power steering, as well as electronic braking, damping and other vehicle-stability control applications.

The V850E/PHO3 also features two CAN interfaces, three LINUART interfaces, and a 32-bit non-multiplexing bus interface for use in advanced network architectures. The MCU comes with a complete, ready-to-use AUTOSAR-compliant Microcontroller Abstraction Layer (MCAL) software stack to facilitate design of standardized and reusable application software.

Renesas Technology America recently added 50 devices to its R32C/100 series of 32-bit microcontrollers (Figure 2), which are built around the R32C/100 32-bit CPU core at the high end of Renesas' M16C family of complex instruction set computer (CISC) MCUs.

The new devices operate at up to 64 MHz and incorporate high-speed flash memory. The 144-pin, 60 MHz R32C/133 and R32C/134 groups, which target x-by-wire applications, feature a dual-channel FlexRay controller and two or three CAN channels.

Paul Kanan, segment marketing manager in Renesas' Automotive Business Unit, said the product line expansion was driven by rising demand for MCUs that have sophisticated on-chip functionality and can deliver the higher levels of performance needed to rapidly execute large amounts of control code.

“A lot of OEMs in North America are doing cost/benefit analyses to determine if it's economically feasible to pull FlexRay IP into next-generation architectures,” Kanan said. “It's a big decision, and it's important for them to understand the overall cost.

“OEMs are definitely active in investigating FlexRay IP. And OEMs and tier one suppliers have real FlexRay silicon from vendors that they can put on the bench and investigate,” Kanan continued. “Customers are looking at interconnection strategies; star and linear architectures; different configurations and systems. We are seeing a critical mass being developed for FlexRay IP. There definitely is movement.”

Kanan said there is some encroachment of FlexRay networks on CAN applications. “Many FlexRay systems are targeting high data rate systems like power steering that are now being implemented in CAN,” he noted.

“There is some removal of CAN networks by firms that want to increase functionality that is associated with FlexRay and not available through CAN, such as the high data rate, and built-in redundancy — for every FlexRay network there are two nodes with the same data, throughout the system. There's also built-in fault tolerance, which CAN does not have. And FlexRay is deterministic. With the current CAN protocol there is reason to worry about losing the battle of priorities of a CAN message. If it's a lower priority, the message might not get through, or not get through in the right amount of time.”

Texas Instruments markets TMS470 and TMS570 automotive microcontrollers (Figure 3) for safety and ABS/ESP, airbag, sensor cluster/chassis controller and steering applications, according to Markus Staeblein, product manager for automotive controllers. The TMS470 and TMS570 MCUs are based on ARM7 and Cortex R4 cores, respectively.

Staeblein said that when OEMs first put out the call for FlexRay chips, vendors looked for a proof of concept and technical evaluation prior to embedding FlexRay into a microcontroller, and so the initial implementation included a separate FlexRay controller. Times have changed. “Now, almost everyone is including FlexRay in their (microcontroller) devices,” he said.

“But at the same time that FlexRay is evolving, there is a trend under way toward more stringent safety standards, so in some cases OEMs and tier one suppliers simply want to replace their CAN networks with FlexRay, but in other cases these customers are taking the opportunity to re-examine their safety system concept.”

The next stage in evolution, which is occurring now, will be embedded FlexRay for braking applications to provide higher bandwidth and fault tolerance, according to Staeblein. Beyond that, more emphasis will be placed on other safety applications like chassis control, sensor clustering, and steering.

Cost is always a key factor when an OEM or tier one supplier selects a microcontroller, but Staeblein noted that FlexRay has just begun to work its way down market. While cost is a factor even in luxury vehicles, it is not as significant a factor as it would be in lower-cost vehicles.

Other key selection criteria include power consumption, performance, code density (size), and quality. Staeblein said current parts per million (ppm) performance and implementation of firewalls and lessons learned are the best measures of a vendor's ability to deliver parts with zero defects. “Reducing power consumption translates to better fuel economy and lower CO2 emissions, and also affects cost,” according to Staeblein. “Performance is best measured by benchmark tests. A microcontroller's performance in a particular application depends on factors like code density and compiler optimization. Customers want ‘headroom’ for meeting future requirements.” Staeblein said past performance is the best measure of a vendor's ability to deliver parts with zero defects.

Infineon's FlexRay system consists of a stand-alone FlexRay protocol controller that can be integrated with 16- and 32-bit microcontrollers for vehicle safety and engine control applications. Based on the FlexRay IP-based technology developed by Robert Bosch GmbH, the protocol controller provides three interfaces: the serial and parallel interface as linkage to the SPI bus and parallel memory bus of current microcontrollers. It also offers the high-speed Micro Link Interface (MLI) to 32-bit Infineon microcontrollers.

In January the firm launched the AUDO FUTURE family of 32-bit microcontrollers based on Infineon's TriCore core, which combines microcontroller and digital signal processor functions and up to 4 MB of flash memory. The devices target automotive powertrain and chassis applications. The family also includes a FlexRay communications block that has been approved by TÜV Nord Group's Institute for Vehicle Technology and Mobility, combined with AUTOSAR software and a peripheral control processor.

“We're shipping FlexRay devices. We have stand-alone and integrated FlexRay controllers, and we also offer an IP block. We don't currently offer any physical layer devices,” said Peter Schulmeyer, director of strategy for Freescale Semiconductor's automotive microcontroller business.

He added that FlexRay is an increasingly common requirement for microcontrollers, both 16- and 32-bit. Freescale's single-chip, 32-bit MPC5567 features a 40-132 MHz e200z6 Power Architecture core, 2 MB of embedded flash with Read While Write (RWW) and Error Correction Coding (ECC) capabilities, and FlexRay protocol. It targets high-end integrated chassis applications as well as engine management and control.

Freescale's 32-bit MPC5561, also based on a 132 MHz e200 Power Architecture core, is optimized for sensor-based collision-avoidance systems. It features 1 MB of embedded flash with RWW and ECC, a high-speed image sensor interface, a single-instruction, multiple-data (SIMD) engine for signal processing and floating point applications, and a FlexRay network controller tailored for automotive safety systems.

For body electronics applications, Freescale offers the 32-bit MPC5510 family, which scales from single-core devices with 384 KB of embedded flash memory to 80 MHz dual-core (e200) MCUs with 1 MB of flash. Target applications include body control modules (BCMs), gateways (linking FlexRay to CAN and LIN networks), instrument cluster controllers, center stack display controllers and smart junction boxes.

Freescale offers FlexRay on 16-bit microcontrollers in its MC9S12XF family. Those devices use a 50 MHz S12x core based on a 16-bit CISC architecture. They target various body, chassis and safety applications and are available in a variety of memory configurations, including 32 KB to 1 MB of on-chip flash. Package options range from the 112-pin low-profile quad flat-pack (LQFP) device to the 10 mm × 10 mm 64-pin LQFP, which is one of the smaller FlexRay controllers available.

“We're shipping FlexRay devices, and we're seeing demand (for FlexRay) picking up,” Schulmeyer said. “There is a lot of activity going on. The original driver for FlexRay was safety critical applications that required redundant communications, but now we are seeing a lot of applications without safety features, where the benefit is gaining higher throughput from FlexRay versus CAN.”

Schulmeyer and other automotive semiconductor executives expect more FlexRay production applications to surface this year.


John Day writes regularly about automotive electronics and other technology topics. He holds a BA degree in liberal arts from Northeastern University and an MA in journalism from Penn State. He is based in Michigan and can be reached by e-mail at [email protected].

COMPANY MENTIONSAustriamicrosystems AUTOSAR BMW FlexRay Consortium Freescale Semiconductor Infineon Technologies JasPar NEC Electronics America NXP Semiconductors Renesas Technology America Robert Bosch GmbH Texas Instruments TÜV Nord

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