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Overview of FlexRay communication protocol
2022-07-07 06:25:00 【AUTOSAR technical support and training】
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In order to meet the endless communication needs of improving vehicle performance , Various agreements already exist .FlexRay It is such a next-generation general high-speed protocol that provides security critical features . Combined multiple sensors 、 The actuator and electronic control unit need to be synchronized to provide high-end performance . Controller area network ( CAN ) Unable to meet the growing demand for bandwidth in today's advanced vehicles . In order to meet these next generation challenges of these advanced vehicles ,FlexRay The agreement has proved to be of great significance in the world of rapid development of Automotive Technology .
FlexRay The communication protocol is a registered trademark of DaimlerChrysler Corporation .FlexRay The full use of is made by FlexRay Alliance in 2008 , launched in , The alliance will promote FlexRay It is standardized as the next generation vehicle communication protocol .FlexRay Designed to meet drive by wire ( Start by wire 、 Brake by wire ) And advanced equipment auxiliary system ( The engine 、 transmission ) Designed for the needs and challenges of .
1 FlexRay Network structure
FlexRay Use unshielded twisted pair to connect nodes . Their cable impedance is about 80-110 ohm , It needs to be terminated at the end node . It's like CAN equally , A resistor is connected between the pair of signal lines to achieve this .
The differential signal on each pair of cables can reduce the impact of external noise on the network , Without expensive shielding . It supports single channel and dual channel configurations , It consists of one or two pairs of lines . Dual channel configuration provides enhanced fault tolerance and increased bandwidth .
2 FlexRay Characteristics
reliable .
Hurry up .
Redundant .
the height is 10 Mbps High data rate .
Flexible configuration .
Multiple topology options .
Fault tolerance .
Event and time trigger .
Dual channel system .
Can be “n” The nodes make up .
Deal with various frameworks .
They tolerate mistakes .
Collision free access .
Ensure message delay .
Fixed communication delay .
all ECU Global synchronization time .
Static and dynamic segments .
Bandwidth ratio CAN high 20 times .
Time division multiple access (TDMA) Manage multiple nodes .
application :
- Electric power steering .( Steer by wire ).
- Advanced driving assistance system .
- powertrain .
- Body control module .
- Battery management system .
- Anti lock braking system .
- Vehicle stability control (VSC).
- Vehicle stability assist (VSA).
3 FlexRay Network topology
FlexRay One of its significant advantages is that it can be arranged inside the vehicle according to the layout of the vehicle . It provides a topology similar to Ethernet , For example, the bus ( Multipoint passive )、 Stars ( Active power ) Connection or connection of these two topologies , be called FlexRay Hybrid topology of the network . This helps designers improve the performance of a given vehicle system design 、 Reliability and optimized cost .
3.1 Multipoint bus FlexRay The Internet
- Commonly used .
- One network cable connects multiple ECU.
- There can only be one at a time ECU transmitted .
- End to end to eliminate signal reflection .
3.2 star FlexRay The Internet
- Each link is connected to the central active node .
- They are used for more extended networks .
- If a node fails , It will not affect other nodes .
- Reducing the number of bare wires helps to improve the anti noise ability .
3.3 blend FlexRay The Internet
- It is composed of bus and star topology .
- Provide the best of the two topologies .
- Cost effective 、 Reliable and easy to use .
**FlexRay Protocol communication cycle :** Fixed in network design ( Usually keep at 1-5ms about ). It consists of four main parts , be called :
- Static segment : Time slot reserved for deterministic data , Arrive in a fixed period .
- Dynamic segment : Adapt to various signals , It will not slow down because of too many static slots FlexRay cycle . It allows the occasional transfer of data .
- Symbol window : Involve network maintenance and identify unique cycles , Such as cold start cycle .
- Network idle time : It is used to maintain synchronization between node clocks by adjusting any drift that may occur in the previous cycle . It always consists of ECU Predefined as a known length .
4 FlexRay Message frame format
For any static or dynamic segment , Each slot consists of a FlexRay The frame of , The frame is divided into three basic parts , As shown below :
4.1 HEADER
4.2 Payload
It contains the actual data that needs to be transmitted by the message frame . Its length is 0 To 254 Bytes .( yes CAN Of 30 times ).
Message-ID( Optional ): this ID Define using the first two bytes of the payload segment . It can be used as filterable data at the receiving end .
NW vector ( Optional ): The length of the network management vector must be 0 To 12 Bytes , And it is common to all nodes .
4.3 Trailer
It contains three hardware specified 8 position CRC value , Used to detect errors by changing the seed value on the connection channel to prevent incorrect connections .
4.4 Data security and error handling
FlexRay The network provides scalable fault tolerance . The option of allowing single channel and dual channel communication makes it more secure . Using these two channels to connect devices on the bus can improve security . Bandwidth can be increased by using two channels to transmit non redundant data .
FlexRay The protocol uses bus protection mechanism to promote rapid error detection in the physical layer 、 Signaling and error control , This mechanism protects the channel from interference caused by communication inconsistent with the cluster communication scheduling .
5 CAN and FlexRay The difference between
For each embodiment ,FlexRay The design of the network may be different . Before joining the bus , Each node must be programmed with the correct network parameters , To achieve normal operation .FlexRay The Committee standardized the storage and transmission format of these parameters in the process of Engineering , To maintain the network configuration between nodes . Fieldbus exchange format or FIBEX File is ASAM The standard of definition , Allow network designers 、 Prototype designer 、 Verifiers and testers can easily share network parameters , And quickly configure ECU、 Test tools, hardware in the loop simulation system, etc .
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