Transcript Netcarbench A Benchmark for Techniques and Tools used in the Design of Automotive Communication Systems Christelle BRAUN Lionel HAVET Nicolas NAVET LORIA-INRIA Campus Scientifique, B.P.

Netcarbench
A Benchmark for Techniques and Tools used in the Design of
Automotive Communication Systems
Christelle BRAUN
Lionel HAVET
Nicolas NAVET
LORIA-INRIA
Campus Scientifique, B.P. 239
54506 Vandoeuvre-les-Nancy, France
[email protected]
{Lionel.Havet,Nicolas.Navet } @loria.fr
FeT‘ 2007, 9th November 2007, Toulouse, France
Outline
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Typical automotive communication networks today

The need for benchmarks
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Our solution: Netcarbench
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In-vehicle embedded systems
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Several communication networks needed in a vehicle
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Body
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Chassis
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Powertrain
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Typical configuration today
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A CAN (Controller Area Network) with 5-25 ECUs (Electronic
Control Units).
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Subject to significant QoS:
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High performance
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Real-time capabilities
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Fault tolerance (not considered yet)
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Issues
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The complexity of these systems keeps increasing :
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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

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In-house
Third-party suppliers
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SymtaVision, 2007
RealTime-at-Work, 2007
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With the software NETCAR-Analyzer (initially developed at LORIA)
Configuration problems :
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Frame packing

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Guarantee the schedulability and minimize the bandwidth consumption.
Setting offsets

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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.
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System model
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Inputs
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Set of N ECUs. For each Nj, a set Sj of signals.
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For each signal si=(Ni,Ti,Oi,Ci,Di)
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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)
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Frame packing
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Goal
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For each ECU Nj with the set Sj of signals, construct the set of
frames Fj={fj1,...,fjk}, such that:
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Fj is schedulable
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The bandwidth consumption is minimized


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None of the transmitted signal misses a deadline.
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]
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Exact complexity shows that no exhaustive approach is possible
[Saket and Navet, 2006]
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Efficient heuristics are required.
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Frame packing
…
Minimize
bandwidth
consumption
and respect
deadline
constraints
F1 F2
ECU1
Frame X
F3 F4
F5 F6
ECU2
Frame Y
F7
ECU3 ECU4
Frame Z
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Setting Offsets
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Output of the frame packing algorithm
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Set of frames of the form fj=(Nj',Tj',Oj',Cj',Dj',Pj')
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Nj',Tj',Oj',Cj',Dj': same meaning as before.
Pj': (unique) priority of the frame.
Goal
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Compute the WCRT in order to check the schedulability of the
messages (with offsets).
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WCRT without offsets calculated in [Tindell and Burns, 1994] and
revised in [Davis, 2007].
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No solution whose complexity is not exponential.
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No reference for WCRT with offsets so far, but commercial
softwares already available (SymtaVision, NETCAR-Analyzer).
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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.
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Taken over by the company RealTime-at-Work in 2007.
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Goals
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Computes exact and very fast WCRT of messages with offsets in
CANs.
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Includes a set of proprietary offset assignment algorithms, finetuned with the experience gained in industrial use.
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Can be improved and extended according to the user's needs.
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NETCAR-Analyser: screenshot
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Benchmark
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How to compare these algorithms and evaluate their efficiency?
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Need for a domain-specific benchmark.
Benchmark
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„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
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Standardization
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Scalability

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Capture the typical properties of the workloads in today‘s automotive
networks (CAN, FlexRay...)
Can be easily adapted to evolutions of the network model.
Customisation
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Let the user define the specific parameters of his application
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Existing benchmarks

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Why is so little information available?
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Confidentiality + competition between car manufacturers.
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Applications restricted to the brand under concern.
Only 2 published benchmarks
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SAE Benchmark
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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
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obsolete
PSA Benchmark
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PSA Peugeot-Citroen, 2000.
Powertrain network with 6 nodes and 12 different periodic messages.
Problem
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obsolete
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Netcarbench


Our solution: Netcarbench
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A new benchmark for broadcast networks in automotive distributed
control systems.
Outperforms existing solutions
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Input
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Output
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User-defined configuration.
Sets of messages complying with the specification and whose
parameters are possibly completed by automatic randomisation.
Implementation
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XML format for the configuration (input file) and the generated
message sets (output files).
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Several examples of typical realistic networks already predefined
for an immediate use.
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Configuration file
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Principles
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Constant parameters defined by the user.
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Variable parameters constrained by the user and instantiated by
Netcarbench.
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Parameters for the overall network
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Type of messages (signals or frames)
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Bandwidth
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<bandwidth Value="125">
Maximal load
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<signals Value="False">
<load Min="30" Max="35">
Number of ECUs
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<ecu Min="15" Max="20">
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Configuration file
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Parameters for the ECUs
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Maximal load
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<s Id="3" Load="0.10">
Parameters for the messages
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Period
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<p Value="50" Weight="2"
PrioLowRange="1" PrioHighRange="200" Margin="1">
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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
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<m Length="8" Weight="10" Margin="2">
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Selects a message with a probability of (Weight±Margin)/SumWeights %.
If the message is selected, it is assigned a length of 8 bits.
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Generated message sets
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Network
<msgset Busspeed="125" Name="set1.xml" Load="32.054">
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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>
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Evaluation (on 100 message sets)
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Lengths of the messages
<messages_sizes>
<m Length="1"
<m Length="2"
<m Length="3"
<m Length="4"
<m Length="5"
<m Length="6"
<m Length="7"
<m Length="8"
</messages_sizes>

Weight="1"
Weight="1"
Weight="1"
Weight="1"
Weight="2"
Weight="2"
Weight="2"
Weight="8"
Margin="1"
Margin="1"
Margin="1"
Margin="1"
Margin="1"
Margin="1"
Margin="1"
Margin="2"
/>
/>
/>
/>
/>
/>
/>
/>
 6 ±6%
 6 ±6%
 6 ±6%
 6±6%
 12 ±6%
 12 ±6%
 12 ±6%
 44 ±12%
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>
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Evaluation: lengths of messages
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Evaluation: loads of the ECUs
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Evaluation results
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Lengths of the messages
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The assigned lengths are within the user-specified range.
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The average length is very close to the specified weight.
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Loads of the ECUs
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The load assigned to a given ECU by Netcarbench may differ from
the value specified by the user, if provided.
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But the compliance is always verified in the average case.
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For unspecified loads, Netcarbench relies on a uniform distribution.
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Conclusion
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Even on a relatively limited number of experiments, the message
sets are representatives of the user's specifications.
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Conclusion
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Netcarbench: a new approach
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Aimed at facilitating the design and comparison of configuration
algorithms and communication protocols.
Genericity
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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
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Can easily be extended to new network designs.
Automation
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Performs automatically all remaining tasks, using randomization for
the missing parameters.
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Conclusion
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Interoperability
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Uses for both input and output XML files, to ease the
interoperability with other software tools.
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Availability
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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
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Future work
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Extension to the method of offsets/deadlines assignment
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Extension to the FIBEX format (Field Bus Exchange Format, 2006)
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Standard available on the ASAM (Association for Standardisation of
Automation and Measuring Systems) website.
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On-going implementation at LORIA.
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Participation of other research groups would be appreciated!
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Open repository of configuration files.
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Creation of a Sourceforge project.
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...
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