Chien-Chih(Paul) ChaoChih-Chiang(Michael) Chang

Instructor: Dr. Ann Gordon-Ross

Introduction of FlexRay

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SummaryGeneral BackgroundPerformance 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 Conclusion2 of 41

General BackgroundWhat is FlexRay?

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When was it released?

Why uses FlexRay?

A next generation automotive network communications protocol.

First public release(Version 2.0) on Jun 2004.The latest version 3.0.1 was released on Oct 2010.

1. High bandwidth2. Flexibility 3. Fault-tolerance4. Reliability

General Background

FlexRayController Area Network(CAN)

10Mbps x 2 bandwidth Time-triggered for

real-time transmissionEvent-triggered for

low-priority dataSynchronousDeterministic system

design

Bandwidth up to 1Mbps

Contention resolved by priority.

AsynchronousAcknowledgment

and retransmission when message is corrupted

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General BackgroundWho developed FlexRay?

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Where used FlexRay?

BMW X5 on 2006, BMW 5-Series, BMW 7-SeriesAudi A8, Bentley Mulsanne, Rolls-Royce Ghost

General BackgroundHow does it work?

Dual channel - scalable system fault-tolerance

Bus GuardianInterconnect topologies: centralized or

bus

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General BackgroundMacrotick- the node’s own internal clock or

timer.Microtick- a cluster wide synchronized

clock.NIT is stand for Network Idle Time which

time corrections.

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Performance Analysis of FlexRay-based ECU Networks

Andrei Hagiescu, Unmesh D. Bordoloi, Samarjit ChakrabortyDepartment of Computer Science, National University of Singapore

Prahladavaradan Sampath, P. Vignesh V. Ganesan, S. RameshGeneral Motors R&D – India Science Laboratory, Bangalore

Design Automation Conference (DAC) 2007,San Diego, California, USA

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MotivationIn 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).

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FlexRay Communication cyclesThe first cycle T1, T3,T5, T6, and T7 have

messages to send.The Second cycle T2 have messages to send.

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Difficulties in Modeling FlexRayA 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, where the maximum length of the message can be equal to the length of the dynamic segment.

One minislot is consumed from the available service when a task is not ready to transfer a message.

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Modeling FlexRayStep 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.

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Modeling FlexRayThe service available to the lower priority

tasks (i.e. T2 …)is made up of two componentsThe service that was unavailable to T1.The service that was unutilized by T1.

The procedure is remaining for the rest tasks.

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

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m1 m2 m3 m4

Results

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ConclusionPresent 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.

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FlexRay Schedule Optimization of the Static SegmentMartin Lukasiewycz, Michael Glaß, and Jürgen TeichUniversity of Erlangen-Nuremberg, GermanyPaul MilbredtI/EE-81, AUDI AG, German

CODES+ISSS 2009, Grenoble, France

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Quick ViewPresenting 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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Background & Introduction

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AUTOSARAUTomotive Open System ARchitecture

FlexRayAn Automotive Communication System

Protocol Data Units (PDUs)

Background – AUTOSARAUTomotive Open System ArchitectureOpen and Standardized automotive software

architecturePartnership for automotive E/E

(Electrics/Electronics) architecturesStandardization

Basic systems functions,Scalability to different vehicle Transferability throughout the networkMaintainability throughout the entire product life-

cycleEtc.

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Background – FlexRayStatic Segment

Time-triggeredEnable a guaranteed real-time transmission of

critical dataPeriodic and Safety-critical dataReserved slots for deterministic data that arrives

at a fixed periodDynamic Segment

Even-triggeredFor low priority dataMaintenance and Diagnosis datadoes not require determinism

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Background – FlexRay (Cont.)Communication Cycle

Symbol WindowTypically used for network maintenance and signaling for starting the network. 

Network Idle TimeA known "quiet" time used to maintain synchronization between node clocks.

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5

Background – FlexRay – Static Seg.Static Segment

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Background – FlexRay – Static Seg.Made up of n equally sized slotseach slots is uniquely assigned to one nodeNode may occupy more than one slot

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1 2 3

Background – FlexRay – Static Seg.Each slot: header, trailer, and payload

segment

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PDU PDU PDU PDU

PDU PDU PDU PDU

Background – PDUs

OSI Layer PDU Name

Application DataData

Presentation

DataData

Session DataData

Transport SegmentSegment

Network PacketPacket

Data Link FrameFrame

Physical BitsBits26 of 41

The mechanism for communicating information between protocols, they are most generally called protocol data units (PDUs).

Motivation

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To minimize the number of used slots in order to maximize the utilization of the busScheduling optimization scheme for the

static segment of the FlexRay bus

Problem definition

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Scheduling Problem:Scheduling Requirements

the static time-triggered segmentWhy optimization?

high flexibility for incremental schedule changes for future automotive networks with a higher data

volumefast scheduling techniques are necessary to allow for an effective parameter exploration

AUTOSAR Interface Specificationcycle multiplexing for a single slotmaximizes the utilization of the static segment in compliance with the high requirements for reliability and robustness

Methodology

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Methodology

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SlotSlot BinBin Optimal

Optimal

Methodology

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Problem TransformationTransform the scheduling problem into a

special two-dimensional bin packing problem1 slot 1 bin

MethodologyBin Packing

The Heuristic Approach“Fast Greedy Heuristic”Better with Unconstrained Problems

ILP ApproachBetter with Constrained Problems:Enhanced ILP

Mutex PackingAdd Mutual Exclusion to the bin packing

ReorderingFor Extensibility of a bin and a slot

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Fast Greedy Heuristic

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“Greedy” implies: Local Optimal Global OptimalTo put “elements” into “bins”

The Order of the elements (by height and weight)Allocated new empty bin

Integer Linear Programming (ILP)

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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 ILPThis constraint improves the runtime of the

ILP: If the optimal solution is reached and equals the lower bound, the optimization process terminates immediately.

Experimental Results

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Schedule OptimizationIncremental SchedulingScalability Analysis

ILP & HeuristicSlot Size ExplorationSupportive Test Case

Results - Schedule OptimizationIntel Pentium 4 3.20 GHz machine with 512

MB RAMhighly heterogeneous in terms of their

period and sizethe only approach currently, TTX Plan

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Results - Incremental SchedulingIn 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.

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Results – Scalability

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Results - Supportive Test CaseBMW series 7Overall 15 nodes91 slots each having a payload of 16 bytes237 random PDUs were generated

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Conclusion

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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

Thank you!

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