The Rise of Ethernet as FlexRay Changes Lanes
There are five popular protocols for in-vehicle networking. Caroline Hayes examines the structure and merits of each.
Today’s vehicles use a range of technologies, systems and components to make each journey a safe, comfortable, and enjoyable experience. From infotainment systems to keep the driver informed and passengers entertained, to Advanced Driver Assistance Systems (ADAS) to keep road users safe, networked systems communicate within the vehicle. Vehicle systems such as engine control, anti-lock braking and battery management, air bags and immobilizers are integrated into the vehicle’s systems. In the driver cockpit, there are instrument clusters and drowsy-driver detection systems, as well as ADAS back-up cameras, automatic parking and automatic braking systems. For convenience, drivers are used to keyless entry, mirror and window control as well as interior lighting, all controlled via an in-vehicle network. All rely on a connected car and in-vehicle communication networks.
LIN targets control within a vehicle. It is a simple, standard UART interface, allowing sensors and actuators to be implemented, as well as lighting and cooling fans to be easily replaced. The single-wire, serial communications system operates at 19.2-kbit/s, to control intelligent sensors and switches, in windows, for example.
This data transfer rate is slower than CAN’s 1-Mbit/s (maximum) operation. CAN is used for high-performance, embedded applications. An evolution of CAN is CAN FD (Flexible Data rate), initiated in 2011 to meet increasing bandwidth needs. It operates at 2-Mbit/s, increasing to 5-Mbit/s when used point-to-point for software downloads. The higher data rate of CAN allows for a two-wire, untwisted pair cable structure, to accommodate a differential signal.
As well as boosting transmission rates, CAN FD extended the data field from 8-byte to 64-byte. When only one node is transmitting, increasing the bit rate is possible, as nodes do not need to be synchronized.
LIN debuted at the same time as vehicles saw more sensors and actuators arrive. At this juncture, point-to-point wiring became too heavy, and CAN became too expensive. Summarizing LIN, CAN and CAN FD, Johann Stelzer, Senior Marketing Manager for Automotive Information Systems (AIS), Automotive Product Group, Microchip, says: “CAN and CAN FD have a broadcast quality. Any node can be the master, whereas LIN uses master-slave communication.”
The higher bandwidth of CAN FD allows for security features to be added. “The larger payload can be used to transfer keys with multiple bytes as well as open up secure communications between two devices,” says Matthias Karcher, Senior Manager AIS Marketing Group, at K2L. The Microchip subsidiary provides development tools for automotive networks.
CAN FD’s ability to use an existing wiring harness to transfer more data from one electronic control unit to another, using a backbone or a diagnostic interface, is compelling, says Stelzer. It enables faster download of driver assistance or infotainment control software, for example, making it attractive to carmakers.
Ethernet as Communications Backbone
Ethernet uses packet data, but at the moment its use is restricted to diagnostics and software downloads. It acts as a bridge network, yet while it is flexible, it is also complex, laments Stelzer. As in-vehicle networks increase, so high-speed switching increases, adding to the complexity, requiring a high power microcontroller or microprocessor as well as requiring validating and debugging, which can add to development time.
In the future, asserts Stelzer, Ethernet will be used as the backbone communications between domains, such as safety, power and control, in the vehicle. When connected via a backbone it will be able to exchange software and data quickly, at up to 100-Mbit/s, or 100 times faster than CAN and 50 times faster than CAN FD.
At present, IEEE 802.3 operates at 100BaseTX, the predominant Fast Ethernet speed. The next stage is to operate at 100BaseT1, which is also 100-Mbit/s Ethernet over a single twisted wire pair. The implementation of Ethernet 100BaseT1 will be big, says Stelzer. “This represents a big jump in bandwidth,” he points out, “with less utilization overhead.” IEEE 802.3bw, finalized in 2014, will deliver 100-Mbit over a single twisted pair wire to reduce wiring, promoting the trend of deploying Ethernet in vehicles.
Increased deployment will come about when the development tools are in place. In each point-to-point node in the network, developers will have to integrate a tool in each section. “[The industry] will need good solutions,” he says, “to avoid overhead.” K2L offers evaluation boards, apps notes, software, Integrated Design Environment (IDE) support and development tools for standard Ethernet in vehicles. The company will announce the availability of support for Standard Ethernet T1 next year.
MOST for Media
MOST relates to high-speed networking and is predominantly used in infotainment systems in vehicles. It addresses all seven layers in the Open Systems Interconnection (OSI) for data communications, not just the physical and data link layers but also system services and apps.
The network is typically a ring structure and can include up to 64 devices. Total available bandwidth for synchronous data transmission and asynchronous data transmission (packet data) is around 23-MBaud.
MOST is flexible, with devices able to be added or removed. Each node becomes the master in the network, controlling the timing of transmission, although adding parameters can add to complexity. One solution, says Karcher, is for a customer to use Linux OS and a Linux driver to handle the generation distribution to encapsulate MOST for the apps layer. This allows the customer to concentrate on designing differentiation into the product. K2L provides software drivers and software libraries for MOST, as well as reference designs for analog front-ends, demonstration kits and evaluation boards. The level of hardware and software support, says Karcher, allows developers to focus on the application. Hardware can connect to MOST and also to CAN and LIN, he continues, adding that tools can connect and safeguard both system and application, reducing complexity and time-to-market.
The FlexRay Consortium, which was disbanded in 2009, developed FlexRay for on-board computing. There have not been any new developments in FlexRay, notes Karcher, who believes its use is limited to safety applications. Although K2L supplies tools to test and simulate FlexRay, “in the long run, it is hard to see a future for FlexRay,” says Karcher, citing the fact that there are no new designs or applications.
Caroline Hayes has been a journalist, covering the electronics sector for over 20 years. She has worked on many titles, most recently the pan-European magazine, EPN.