Chassis & Suspension
Getting FlexRay Under Control (Part 1) – Physical Layer Basics and Model Generation
Due to the rapid development and standardization of FlexRay, it has already been deployed in a variety of production vehicles. However, most automotive companies have not yet gained much practical experience with FlexRay, particularly with its physical layer. For this reason, development cycles are slow and partly based on trial and error. FlexRay and CAN physical layers may be similar from a theoretical point of view, but differ significantly in practical terms.
The knowledge of the more familiar CAN physical layer cannot simply be applied to the deployment of FlexRay topologies. The FlexRay Consortium addresses this issue in part by providing development support through specification criteria, guidelines and application notes. However, it is the system developer's responsibility to individually check each topology for proper functionality. Checking the FlexRay physical layer specification criteria requires analyzing the target topology, which is not available during the concept phase. As a result, system developers are forced to rely on their intuition and experience. Utilizing simulationbased design methodologies, however, allows developers to realize FlexRay´s deterministic concept and accurately predict the final results.
A simulation-based methodology enables the evaluation of FlexRay criteria during the early phases of development using virtual topologies. This improved design process means significant value by decreasing overall design time.
Basics of FlexRay Networking Systems FlexRay is a flexible networking solution that supports a high bandwidth and deterministic communication scheme. In addition, features such as a second communication channel support safety critical aspects of networking systems. An example of the FlexRay communication cycle structure with four segments is shown in figure 1:
Figure 1: FlexRay Communication Cycle
The slot length within the static segment is fixed by configuration. Within the dynamic segment, the slot length may vary, depending on the required length of the message frames. Figure 2 shows the structure of FlexRay frames. Each message frame starts with a Transmission Start Sequence (TSS), which consists of a user-defined number of logical low bits (0). The TSS is used to inform the network about the start of communication to ensure that the gates of active stars are opened for communication.
The actual user data, also known as payload, is then mapped to a configurable number of bytes within the message frame. Each byte starts with a so-called Byte Start Sequence (BSS). The trailing edge of the BSS is used for synchronizing the local clock of each FlexRay node with the global clock. Timing tolerances within the system are thereby balanced. FlexRay frames are terminated with a Frame End Sequence (FES). In the dynamic segment, the FES is followed by a Dynamic Trailing Sequence (DTS) that is used for back-filling the time until the next minislot. Detailed information regarding the communication process can be found in .
Fig. . 2: FlexRay Frame Structure
To read the entire article, click here
- No news
- Jaguar docks on to Intel for next-gen infotainment systems
- Interface integrates e-vehicles into smart grid
- Kvaser proposes backward-compatible, high-bandwidth CAN version
- Smart cars offer "once in a generation chance" to UK industry, experts say
- Get your digital copy of EETimes Europe
- Women demand different connectivity functions in the car
- EV market is much more than passenger cars - and it's booming
- Emergency Steer Assistant can avoid collisions
- Faurecia, Magneti Marelli jointly integrate tablets and smartphones into cars
- MOST 150 Star topology interconnects driver assistant systems
- Field test fathoms out economic potential for electric mobility
- Researchers significantly improve lithium-air batteries
- Volvo starts large test with robot cars on public roads
- Automotive drives new processor architectures
- Haptic feedback touchpad contributes to driving safety