1. Introduction of FlexRay
Chien-Chih(Paul) Chao
Chih-Chiang(Michael) Chang
Instructor: Dr. Ann Gordon-Ross
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2. Summary General Background
Performance Analysis of FlexRay-based ECU Networks
Motivations
Basic framework
Modeling FlexRay
Case Study
Conclusion
FlexRay Schedule Optimization of the Static Segment
Background & Introduction
Motivation
Problem definition
Methodology
Experimental Results

3. General Background When was it released? What is FlexRay?
A next generation automotive network communications protocol.
When was it released?
First public release(Version 2.0) on Jun 2004.
The latest version was released on Oct 2010.
Why uses FlexRay?
Fault-tolerance
High bandwidth
Flexibility
Fault-tolerance
Reliability
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4. General Background 10Mbps x 2 bandwidth
FlexRay
Controller Area Network(CAN)
10Mbps x 2 bandwidth
Time-triggered for real-time transmission
Event-triggered for low- priority data
Synchronous
Deterministic system design
Bandwidth up to 1Mbps
Contention resolved by priority.
Asynchronous
Acknowledgment and retransmission when message is corrupted

5. General Background Who developed FlexRay? Where used FlexRay?
BMW X5 on 2006, BMW 5-Series, BMW 7-Series
Audi A8, Bentley Mulsanne, Rolls-Royce Ghost

6. General Background How does it work?
Dual channel - scalable system fault-tolerance
Bus Guardian
Interconnect topologies: centralized or bus
A node that watches the operation of a network and takes action when it sees erroneous behavior is known as a bus guardian (whether the network is actually a bus or not). FlexRay uses bus guardians to check for errors on active stars.
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7. General Background Macrotick- the node’s own internal clock or timer.
Microtick- a cluster wide synchronized clock.
A macrotick always includes an integral number of microticks, but different macroticks can contain different numbers of microticks to correct for differences between the nodes’ local clocks. The boundaries between some macroticks are designated as action points, which form the boundaries for static and dynamic segments.
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8. Performance Analysis of FlexRay-based ECU Networks
Andrei Hagiescu, Unmesh D. Bordoloi, Samarjit Chakraborty
Department of Computer Science, National University of Singapore
Prahladavaradan Sampath, P. Vignesh V. Ganesan, S. Ramesh
General Motors R&D – India Science Laboratory, Bangalore
Design Automation Conference (DAC) 2007,
San Diego, California, USA

9. Motivation
In a high-end car there are up to 70 electronic control units (ECUs) exchanging up to 2500 signals.
Commonly used protocols include CAN, local interconnection network(LIN).
Previous implementations of FlexRay using only static segment, with the dynamic segment being unutilized.
Dynamic part of protocol is more complex.
The potential messages for dynamic segment is more irregular.
Techniques for analyzing the static segment are known(TDMA scheme).
TDMA: Time division multiple access
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10. Basic Framework

11. Difficulties in Modeling FlexRay
A message cannot straddle two communication cycles.
Once a task misses in the dynamic segment, it will wait till the next cycle.
A task can send at most one message in each dynamic segment.
One minislot is consumed from the available service when a task is not ready to transfer a message.

12. Modeling FlexRay
Step 1: Extract k1 minislots of service during each communication cycle from l .
Step 2: Discretize the service bound obtained from step 1.
Step 3: The resulting service bound is shifted by d time units.
Step 4:A minislot is lost even when a task does not transmit any message.

13. Modeling FlexRay

14. Case Study Adaptive Cruise Control application.
Implemented framework using Matlab as a front-end.
Using Java to handle all the function transformation.

15. Results

16. Conclusion
Present a compositional performance model for a network of ECUs communicating via FlexRay bus.
Formal model of the protocol governing the dynamic segment of FlexRay.
The framework can also be used for deriving the parameters of the FlexRay protocol.
Help in resource dimensioning and determining optimal scheduling policies for multitasking ECUs.

17. FlexRay Schedule Optimization of the Static Segment
Martin Lukasiewycz, Michael Glaß, and Jürgen Teich
University of Erlangen-Nuremberg, Germany
Paul Milbredt
I/EE-81, AUDI AG, German
CODES+ISSS 2009, Grenoble, France
This is a test!17
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18. Quick View
Presenting a Scheduling Optimization scheme for the static segment of the FlexRay bus in compliance with the AUTOSAR specification.
What is AUTOSAR?
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19. Background & Introduction
AUTOSAR
AUTomotive Open System ARchitecture
FlexRay
An Automotive Communication System
Protocol Data Units (PDUs)
Put some pictures of ECUs!!! No need for ECU
Since we have already know the FlexRay, an automotive communication system, and the ECUs, the Electronic Control Units, we know that there are hundreds of ECUs in the automotive networks.
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20. Background – AUTOSAR AUTomotive Open System Architecture
Open and Standardized automotive software architecture
Partnership for automotive E/E (Electrics/Electronics) architectures
Standardization
Basic systems functions,
Scalability to different vehicle
Transferability throughout the network
Maintainability throughout the entire product life-cycle
Etc.
AUTOSAR (AUTomotive Open System ARchitecture) is an open and standardized automotive software architecture, jointly developed by automobile manufacturers, suppliers and tool developers. It is a partnership of automotive OEMs, suppliers and tool vendors whose objective is to create and establish open standards for automotive E/E (Electrics/Electronics) architectures that will provide a basic infrastructure to assist with developing vehicular software, user interfaces and management for all application domains. This includes the standardization of basic systems functions, scalability to different vehicle and platform variants, transferability throughout the network, integration from multiple suppliers, maintainability throughout the entire product life-cycle and software updates and upgrades over the vehicle's lifetime as some of the key goals.
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21. Background – FlexRay Static Segment Dynamic Segment Time-triggered
Enable a guaranteed real-time transmission of critical data
Periodic and Safety-critical data
Reserved slots for deterministic data that arrives at a fixed period
Dynamic Segment
Even-triggered
For low priority data
Maintenance and Diagnosis data
does not require determinism

22. Background – FlexRay (Cont.)
Communication Cycle
Symbol Window Typically used for network maintenance and signaling for starting the network. 
Network Idle Time A known "quiet" time used to maintain synchronization between node clocks. 5
The FlexRay communication cycle is the fundamental element of the media-access scheme within FlexRay. The duration of a cycle is fixed when the network is designed, but is typically around 5 ms.  There are four main parts to a communication cycle
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23. Background – FlexRay – Static Seg.
Static Segment
The static segment, represented as the blue portion of the frame, is the space in the cycle dedicated to scheduling a number of time-triggered frames.  The 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 that time passes, the ECU must wait until the next cycle to transmit its data in that slot.  Because the exact point in time is known in the cycle, the data is deterministic and programs know exactly how old the data is. This is extremely useful when calculating control loops that depend on consistently spaced data.  The Figure on the Top illustrates a simple network with four static slots being used by three ECUs. Actual FlexRay networks may contain up to several dozen static slots.  
If an ECU goes offline or decides not to transmit data, its slot remains open and is not used by any other ECU, as shown in Figure on th bottom.
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24. Background – FlexRay – Static Seg.
Made up of n equally sized slots
each slots is uniquely assigned to one node
Node may occupy more than one slot 1 2 3

25. Background – FlexRay – Static Seg.
Each slot: header, trailer, and payload segment
PDU
PDU
PDU
PDU
Each slot consists of a header and trailer segment and a payload segment that is statically configured to carry between 0 and 254 bytes.
Since FlexRay is a deterministic system, there is a sequence how these segments are transmitted on the network.
As this Figure indicates, the header segment appears first, followed by the payload segment, and then followed by the trailer segment, which is transmitted last. The FlexRay header segment consists of 5 bytes. These bytes contain the reserved bit, the payload preamble indicator, the null frame indicator, the sync frame indicator, the startup frame indicator, the frame ID, the payload length, the header CRC (cyclic redundancy check code), and the cycle count.
By a predefined schedule, each slot is filled with the communication data of the applications, the protocol data units (PDUs)
PDU
PDU
PDU
PDU
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26. Background – PDUs
The mechanism for communicating information between protocols, they are most generally called protocol data units (PDUs).
OSI Layer
PDU Name
Application
Data
Presentation
Session
Transport
Segment
Network
Packet
Data Link
Frame
Physical
Bits

27. Motivation
To minimize the number of used slots in order to maximize the utilization of the bus
Scheduling optimization scheme for the static segment of the FlexRay bus

28. Problem definition Scheduling Problem: Scheduling Requirements
the static time-triggered segment
Why optimization?
high flexibility for incremental schedule changes
for future automotive networks with a higher data volume
fast scheduling techniques are necessary
to allow for an effective parameter exploration
AUTOSAR Interface Specification
cycle multiplexing for a single slot
maximizes the utilization of the
static segment in compliance with
the high requirements for reliability
and robustness
the periodic and safety-critical data is scheduled on the static time-triggered segment while the dynamic segment is mainly used for maintenance and diagnosis data.
a schedule optimization that minimizes the number of used slots is necessary to:
allow a high flexibility for incremental schedule changes.
for future automotive networks with a higher data volume
Hence, an efficient schedule optimization of the static segment is the key to the success of the FlexRay bus.
And! Also, fast scheduling techniques are necessary to allow for an effective parameter exploration
cycle multiplexing is used to increase the utilization of the FlexRay bus.
The cycle multiplexing of PDUs is defined by the base cycle and the cycle repetition:
The base cycle defines the offset in cycles for the first occurrence of the respective PDU.
The cycle repetition denotes the frequency of a PDU in the multiplexing.
An example of scheduling three PDUs m0, m1, and m2 is given in this Figure.
The base cycle values are 0 for m0 and m1 as well as 3 for m2.
The repetition values are 1 for m0, 2 for m1, and 4 for m2.
Given a common duration of a single communication cycle of 5 ms,
the message m0 is sent each cycle with a period of 5 ms,
the message m1 each second cycle with a period of 10 ms,
and the message m2 each fourth cycle with a period of 20 ms.
The cycle multiplexing technique maximizes the utilization of the static segment in compliance with the high requirements for reliability and robustness and, therefore, is integrated into real-world automotive implementations of the FlexRay bus based on the AUTOSAR specification.
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29. Methodology
1. At First we have already known the requirement of the optimization:
The main goal is to minimize the number of used slots in order to maximize the utilization of the bus.
2. And, then the transformation of the original slot packing problem into a special bin packing problem is performed using
the proposed transformation scheme.
3. The bin packing is carried out in order to minimize the number of allocated slots.
4. Afterwards, the proposed reordering heuristic is used to further maximize the extensibility of the allocated slots by varying
the position and base cycles of the PDUs in the slots.
5. Finally, the transformation is inverted to convert the solution of the bin packing to a feasible FlexRay schedule.
6. Since each slot is assigned to at most one ECU, the scheduling for each ECU is done independently and the slots are put together
in the final schedule.
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30. Methodology
Slot
Bin
Optimal
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31. Methodology Problem Transformation
Transform the scheduling problem into a special two- dimensional bin packing problem
1 slot  1 bin
Constraints
AS SIMPLE AS POSSIBLE!
Problem Transformation:
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32. Methodology Bin Packing Reordering The Heuristic Approach ILP Approach
“Fast Greedy Heuristic”
Better with Unconstrained Problems
ILP Approach
Better with Constrained Problems:
Enhanced ILP
Mutex Packing
Add Mutual Exclusion to the bin packing
Reordering
For Extensibility of a bin and a slot

33. Fast Greedy Heuristic “Greedy” implies: Local Optimal  Global Optimal
To put “elements” into “bins”
The Order of the elements (by height and weight)
Allocated new empty bin
Draw some pictures of Elements and Bins!!
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34. Integer Linear Programming (ILP)
Placing the elements starting from the highest element to the most left void space in the bin s at the level l results in a feasible solution of the bin packing problem.
Enhanced ILP
This constraint improves the runtime of the ILP: If the optimal solution is reached and equals the lower bound, the optimization process terminates immediately.

35. Experimental Results Schedule Optimization Incremental Scheduling
Scalability Analysis
ILP & Heuristic
Slot Size Exploration
Supportive Test Case

36. Results - Schedule Optimization
Intel Pentium GHz machine with 512 MB RAM
highly heterogeneous in terms of their period and size
the only approach currently, TTX Plan
Currently, the only available automatic scheduling approach compliant with the AUTOSAR specification is
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37. Results - Incremental Scheduling
In contrast to the ILP approach, the heuristic scheduling method allows an incremental scheduling.
An incremental scheduling might be favored if the number of allocated slots is still not critical since integration tests are time-consuming and expensive.

38. Results – Scalability

39. Results - Supportive Test Case

40. Conclusion
There exists no publication regarding the FlexRay bus scheduling in compliance with the industrial AUTOSAR Interface Specification.
The case study show that the heuristic and ILP approach are superior to a commercial tool in runtime and quality.
A supportive case study shows the flexibility and robustness of the proposed algorithms
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41. Thank you!