This is a comprehensive overview on FlexRay. This will equip you with necessary basic knowledge on the topic. And as an added perk, I have shared extra information in the "Notes" field below the slides. Happy learning!

1. The FLEXRAY Protocol
By Roja Ramani Pradhan (ESD-BEG)

2. • Introduction
• Why FlexRay?
• Network topology
• Structure of a FlexRay node
• The communication cycle
• Applications
• Conclusion

3. Introduction
The FlexRay Consortium was made up of the following core members:
• Freescale Semiconductor
• Robert Bosch GmbH
• NXP Semiconductors
• BMW AG
• Volkswagen AG
• Daimler AG
• General Motors
2007-2008 BMW X5 photographed in Gainesville, Virginia, USA.

4. Why FlexRay?
FlexRay delivers:
• Time determinism performance
• Fault tolerance
• High speed

5. Why FlexRay?
Bus LIN CAN FlexRay
Speed 40kbps 1Mbps 10Mbps
Cost $ $$ $$$
Wires 1 2 2 or 4
Typical applications Body electronics Powertrain High-end applications
A comparison among LIN, CAN and FlexRay:

6. Why FlexRay?
Many aspects of FlexRay are designed to keep costs down while delivering
top performance in a rugged environment.
• FlexRay uses unshielded twisted pair cabling.
• FlexRay supports single and dual-channel configurations.
• Most first-generation FlexRay networks only utilize one channel to keep wiring costs
down

7. Why FlexRay?
Bus Level
Emissions are limited by the relatively low differential voltages. (Differential signaling
between Bus Plus (BP) and Bus Minus(BM))
• 2V for data_1
• -2V for data_0
Cabling impedance is 80-110Ω
as FlexRay specifies a load of
40-55 Ω

8. Network topology
FlexRay supports
• Simple multi-drop passive connections
• Active star connections (for complex networks)
Multi-drop bus Star network

9. Network topology
Future FlexRay networks will likely consist of hybrid networks i.e. the combination of bus
and star topology.
Hybrid network
Bus topology
(Ease of use, cost advantages)
Star topology
(Performance, reliability)
Hybrid network

10. Structure of a FlexRay node
Controller part
• Host CPU
• Communication controller
Driver part
• Bus guardian
• Bus driver

11. Structure of a FlexRay node
Communication Controller (FlexRay Controller)
• Framing
• Bus access
• Error detection and handling
• Synchronization
• Puts the FlexRay bus to sleep and wakes it up
• Codes TX messages and decodes RX messages.

12. Structure of a FlexRay node
FlexRay node with stand-alone FlexRay controller
FlexRay node with integrated FlexRay controller

13. Structure of a FlexRay node
Bus Guardian
• Prevents disharmony caused by unauthorized transmissions within time slots not
assigned to the nodes.
• Only allows the Bus Driver to place data received from the FlexRay controller on
the bus, if it conforms to the communication schedule.

14. Structure of a FlexRay node
Bus Driver (FlexRay transceiver)
• Couples the FlexRay controller to the physical transmission medium
• Signal transformation- It transforms the logical signal stream received by
the FlexRay controller into a physical signal stream and transforms the received
physical signal stream into a logical signal stream.

15. The Communication Cycle
• The duration of a cycle is fixed when
the network is designed.
• The duration is typically 1-5ms.
• A communication cycle is made up
of a defined number of macroticks
and the macroticks are composed of
a number of microticks, the smallest
time unit of the local clocks.
• Macroticks are often 1µs long.

16. The Communication Cycle
Static Segment

17. The Communication Cycle
Static Segment
• This is the space in the cycle dedicated to scheduling a no. of time-triggered frames.
• This segment is broken up into slots, each slot containing a reserved frame of data.
• When each slot occurs in time, the reserved ECU has the opportunity to transmit its
data into that slot.
• Once the time passes, the ECU must wait until the next cycle to transmit its data in that
slot.
• If an ECU goes offline or decides not to transmit data, its slot remains open and is not
used by any other ECU.

18. The Communication Cycle
Dynamic Segment

19. The Communication Cycle
Dynamic Segment
• It serves to transmit event driven messages.
• It always exhibits the same length.
• Minislots are pre-assigned to each frame of data that is eligible for transmission.
• Once a minislot occurs, an ECU has a brief opportunity to broadcast its frame.
• If it doesn’t broadcast, it loses its spot in the dynamic frame and the next minislot occurs.
• A minislot is typically a Macrotick (1µs) long.

20. The Communication Cycle
Symbol Window
• The symbol window serves to transmit symbols.
• The collision avoidance symbol is used to indicate the start of the first
communication cycle to a FlexRay node.
• The media test symbol is used for testing of a bus guardian.
• The wake-up symbol is used for waking up the FlexRay cluster.

21. The Communication Cycle
Network Idle Time
• It is a pre-defined known length by ECUs.
• The part of time-base correction is performed during the network idle time.
• The ECUS make use of this idle time to make adjustments for any drift that may
have occurred during the previous cycle.

22. The Communication Cycle
Frame Format
Each slot of static or dynamic segment is divided into 3 segments.
• Header
• Payload
• Trailer

23. The Communication Cycle
Header
It is 5 bytes (40 bits) long.
• Status bits - 5 bits
• Frame ID – 11 bits
• Payload length – 7 bits
• Header CRC – 11 bits
• Cycle count – 6 bits

24. The Communication Cycle
Payload
It is upto 127 words (254 bytes)
long.
It contains the actual data
transferred by the frame.
The length is over 30 times
greater than CAN.

25. The Communication Cycle
Trailer
It contains 3 8-bit CRCs to detect errors

26. Applications
• Recent introductions indicate that automakers have a definitive FlexRay rollout plan.
And, BMW is ahead in this race with the implementation of FlexRay v2.1 for active
damping control.
• Although, initially envisioned as an enabling technology for automotive X-by-wire
(drive-by-wire, steer-by-wire) applications, it is now being adopted for other
applications like improving manufacturing efficiencies, safety regulations and the
convenience features. This technology is being enabled by integrated complex
microcontrollers and transceivers.

27. Conclusion
• FlexRay focuses on a set of core needs for today’s automotive industry, including
higher data rates than previous standards, flexible data communications, versatile
topology options, and fault-tolerant operation.
• FlexRay thus delivers the speed and reliability required for next-generation in-car
control systems.

28. 1. https://en.wikipedia.org/wiki/FlexRay
2. https://www.ni.com/en-gb/innovations/white-papers/06/flexray-automotive-
communication-bus-overview.html
3. https://automotivetechis.wordpress.com/flexray/
4. https://svn.ipd.kit.edu/nlrp/public/FlexRay/FlexRay%E2%84%A2%20Protocol%20S
pecification%20Version%203.0.1.pdf
References