A Benchmark for Techniques and Tools used in the Design of Automotive Communication Systems Christelle BRAUN Lionel HAVET Nicolas NAVET FeT‘ 2007, 9th.

A Benchmark for Techniques and Tools used in the Design of

Automotive Communication Systems

Christelle BRAUN

Lionel HAVET

Nicolas NAVET

FeT‘ 2007, 9th November 2007, Toulouse, France

LORIA-INRIA

Campus Scientifique, B.P. 239

54506 Vandoeuvre-les-Nancy, France

[email protected] {Lionel.Havet,Nicolas.Navet } @loria.fr

Netcarbench

11/09/07 Netcarbench

C. Braun, L. Havet, N. Navet 2

Outline

Typical automotive communication networks today

The need for benchmarks

Our solution: Netcarbench



In-vehicle embedded systems

Several communication networks needed in a vehicle Body Chassis Powertrain

Typical configuration today A CAN (Controller Area Network) with 5-25 ECUs (Electronic Control

Units).

Subject to significant QoS: High performance Real-time capabilities Fault tolerance (not considered yet)



Issues

The complexity of these systems keeps increasing : Up to 70 ECUs and 2500 signals in luxury cars. Leads to an extensive use of electronics .

Necessity for algorithms and tools which automate and optimise the control of the communication

In-house Third-party suppliers

SymtaVision, 2007 RealTime-at-Work, 2007

With the software NETCAR-Analyzer (initially developed at LORIA)

Configuration problems : Frame packing

Guarantee the schedulability and minimize the bandwidth consumption. Setting offsets

May lead to double the global load in the network. Further information to be published soon in the Automotive embedded Handbook,

N. Navet, F. Simonot-Lion editors, CRC Press/Taylor and Francis, 2008.



System model

Inputs Set of N ECUs. For each Nj, a set Sj of signals. For each signal si=(Ni,Ti,Oi,Ci,Di)

Ni: the ECU it belongs to Ti: the period of production Oi: the offset Ci: the size in bits Di: the relative deadline (here Di=Ti)



Frame packing

Goal For each ECU Nj with the set Sj of signals, construct the set of frames Fj={fj1,...,fjk}, such

that: Fj is schedulable

None of the transmitted signal misses a deadline. The bandwidth consumption is minimized

Important for practical applications In LORIA, research on the optimisation method of offsets assignment (adding offsets to better distribute

the load) [Grenier 2008]

Complexity Frame packing is NP-hard [Norström, 2000] Exact complexity shows that no exhaustive approach is possible [Saket and Navet, 2006] Efficient heuristics are required.



……

ECU4ECU4ECU3ECU3ECU2ECU2ECU1ECU1F2F2F1F1 F3F3 F4F4 F5F5 F6F6 F7F7

Frame XFrame X Frame YFrame Y Frame Z Frame Z

Minimize bandwidth

consumption and respect

deadline constraints

Frame packing



Setting Offsets

Output of the frame packing algorithm Set of frames of the form fj=(Nj',Tj',Oj',Cj',Dj',Pj')

Nj',Tj',Oj',Cj',Dj': same meaning as before. Pj': (unique) priority of the frame.

Goal Compute the WCRT in order to check the schedulability of the messages (with

offsets). WCRT without offsets calculated in [Tindell and Burns, 1994] and revised in [Davis,

2007]. No solution whose complexity is not exponential. No reference for WCRT with offsets so far, but commercial softwares already

available (SymtaVision, NETCAR-Analyzer).



NETCAR-Analyzer

History Initially developed at LORIA in the authors' research group. Motivation: no tool available for the computation of response times with offsets

on large sets of messages. Taken over by the company RealTime-at-Work in 2007.

Goals Computes exact and very fast WCRT of messages with offsets in CANs. Includes a set of proprietary offset assignment algorithms, fine-tuned with the

experience gained in industrial use. Can be improved and extended according to the user's needs.



NETCAR-Analyser: screenshot



Benchmark

How to compare these algorithms and evaluate their efficiency? Need for a domain-specific benchmark.

Benchmark „Standard by which something is evaluated or measured.“

[Wiktionary] What we need here

Generation of workloads which simulate the data exchange between the ECUs.

3 challenges Standardization

Capture the typical properties of the workloads in today‘s automotive networks (CAN, FlexRay...)

Scalability Can be easily adapted to evolutions of the network model.

Customisation Let the user define the specific parameters of his application



Existing benchmarks

Why is so little information available? Confidentiality + competition between car manufacturers. Applications restricted to the brand under concern.

Only 2 published benchmarks SAE Benchmark

Society of Automotive Engineers, 1993. Initially developed for a point-to-point network. Adapted by Tindell and Burns to a CAN composed of 7 ECUs exchanging

53 messages (1994). Problem

obsolete PSA Benchmark

PSA Peugeot-Citroen, 2000. Powertrain network with 6 nodes and 12 different periodic messages. Problem

obsolete



Netcarbench

Our solution: Netcarbench A new benchmark for broadcast networks in automotive distributed

control systems. Outperforms existing solutions

Input User-defined configuration.

Output Sets of messages complying with the specification and whose

parameters are possibly completed by automatic randomisation. Implementation

XML format for the configuration (input file) and the generated message sets (output files).

Several examples of typical realistic networks already predefined for an immediate use.



Configuration file

Principles Constant parameters defined by the user. Variable parameters constrained by the user and instantiated by

Netcarbench.

Parameters for the overall network Type of messages (signals or frames)

<signals Value="False"> Bandwidth

<bandwidth Value="125"> Maximal load

<load Min="30" Max="35"> Number of ECUs

<ecu Min="15" Max="20">



Configuration file

Parameters for the ECUs Maximal load

<s Id="3" Load="0.10"> Parameters for the messages

Period <p Value="50" Weight="2" PrioLowRange="1" PrioHighRange="200" Margin="1">

Selects a message with a probability of (Weight±Margin)/SumWeights %. If the message is selected, it is assigned a period of 50ms and a (random)

unused priority between 1 and 200.

Length <m Length="8" Weight="10" Margin="2">

Selects a message with a probability of (Weight±Margin)/SumWeights %. If the message is selected, it is assigned a length of 8 bits.



Generated message sets

Network<msgset Busspeed="125" Name="set1.xml" Load="32.054">

Messages assigned sequentially to the ECUs<ecu Name="Ecu_0"> <frame Name="frame67" Priority="23" Period="100" Length="8"/> <frame Name="frame68" Priority="42" Period="50“ Length="4"/> ...</ecu>



Evaluation (on 100 message sets)

Lengths of the messages<messages_sizes>

<m Length="1" Weight="1" Margin="1" /> 6 ±6% <m Length="2" Weight="1" Margin="1" /> 6 ±6% <m Length="3" Weight="1" Margin="1" /> 6 ±6% <m Length="4" Weight="1" Margin="1" /> 6±6% <m Length="5" Weight="2" Margin="1" /> 12 ±6% <m Length="6" Weight="2" Margin="1" /> 12 ±6% <m Length="7" Weight="2" Margin="1" /> 12 ±6% <m Length="8" Weight="8" Margin="2" /> 44 ±12%

</messages_sizes>

Loads of the ECUs<loaded_stations>

<s Id="1" Load="0.30" /><s Id="2" Load="0.15" /> <s Id="3" Load="0.10" />

</loaded_stations>



Evaluation: lengths of messages



Evaluation: loads of the ECUs



Evaluation results

Lengths of the messages The assigned lengths are within the user-specified range. The average length is very close to the specified weight.

Loads of the ECUs The load assigned to a given ECU by Netcarbench may differ from

the value specified by the user, if provided. But the compliance is always verified in the average case. For unspecified loads, Netcarbench relies on a uniform distribution.

Conclusion Even on a relatively limited number of experiments, the message

sets are representatives of the user's specifications.



Conclusion

Netcarbench: a new approach Aimed at facilitating the design and comparison of configuration

algorithms and communication protocols. Genericity

Provides the main elements of today's mostly used automotive communication networks (CAN, FlexRAy...)

Customisation Supports a user-defined configuration following the specificities of

the application under concern. Scalability

Can easily be extended to new network designs. Automation

Performs automatically all remaining tasks, using randomization for the missing parameters.



Conclusion

Interoperability Uses for both input and output XML files, to ease the

interoperability with other software tools.

Availability The complete program and all accompanying material are licensed

under the GNU GPL v.2 and can be downloaded at:http://www.loria.fr/~nnavet/netcarbench



Future work

Extension to the method of offsets/deadlines assignment

Extension to the FIBEX format (Field Bus Exchange Format, 2006) Standard available on the ASAM (Association for Standardisation of

Automation and Measuring Systems) website. On-going implementation at LORIA.

Participation of other research groups would be appreciated! Open repository of configuration files. Creation of a Sourceforge project. ...

A Benchmark for Techniques and Tools used in the Design of Automotive Communication Systems Christelle BRAUN Lionel HAVET Nicolas NAVET FeT‘ 2007, 9th.

Documents

netcarbench slide

ti slide

complexity frame packing

set sj of signals

frame packing goal

vehicle embedded systems

set of frames fj

loria configuration