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Guaranteeing Hard Real-Time Requirements of In-Vehicle Multi-hop Communication Over Ethernet
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Transcript of Guaranteeing Hard Real-Time Requirements of In-Vehicle Multi-hop Communication Over Ethernet
Guaranteeing Hard Real-Time Requirements of In-Vehicle Multi-hop Communication Over Ethernet
(12AE-0076/2012-01-0193)
Standard Ethernet for time dependant and time critical applications
Lars BrohneCEO
April 2012
Presentation content
• One minute TCN• Background • Challenges in-vehicle communications• Challenges in guaranteed analysis• Desired features and functionalities of a tool• Conclusion and future Work
2012-01-01932012-01-01932012-01-0193
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One minute TCN
• Time Critical Networks (TCN) produces softwareo Modeling – TCN TimeAnalyzer™o Verification – TCN StreamAnalyzer™
• Worst Case Holistic Response Time Analysiso Predict worst-case end-to-end reaction and age timeo Create cost-effective & robust hybrid CAN/switched
Ethernet systems Latency, jitter and no packet-drop guarantees
• Start-up under Chalmers Innovation – 2008o Unique patent-pending technology from years of research
Real-time systems and schedulability analysis
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Background
• Switched Ethernet starts to be considered for automotive architectureso Today used for fast batch transfers for sw updateo Planned for real-time traffic as wello More bandwitdh is the main driver
Camera systems and streaming video
• Design efficient and secure automotive Ethernet systemso Communication response time analysis will be importanto But how can we make a guaranteed analysis?
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Challenges in-vehicle communications
• Several tens of computers (ECUs)o In-vehicle electronic architecture will be
more complex, distributed, interconnected and interdependent
• Precise timing and prioritization of functions are essentialo For both safety and comforto Functions will depend on timing and
reliability constraints
• Make a design that is cost-effectiveo Right level with regard to performance,
energy consumption and cost
55 ECUs & 7 Buses of 4 types with Gateways
© Daimler Mercedes –Benz & Chrysler
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Challenges in-vehicle communications
• Switched Ethernet starts to be considered for automotive architectureso Guaranteed deliveryo Latency guaranteedo Time synchronizationo Redundancy
55 ECUs & 7 Buses of 4 types with Gateways
© Daimler Mercedes –Benz & Chrysler
2012-01-0193
Challenges in guaranteed analysis
• Traffic model and critical instanceso Proper models need to
be identified Representing real
traffic– Such as GMF
Eg. Periodic and sporadic data flows
o Critical instances may vary according to different models
Worst case scenarios
P
C
D
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Challenges in guaranteed analysis
• Serialization Phenomenon o In a multi-hop network, two related flows may
share several links, but they may not interfere each other over every link
o The extra queuing delay needs to be removed, otherwise we may get pessimistic results
E1
E2
E3
E4
Flow1: E1->E3
Flow2: E2->E4
S1 S2 S3
E5
Flow3: E5->E4
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Challenges in guaranteed analysis
• Indirect Interferenceo Sometimes two flows do not share any link, it seems that they are not related
But actually, they can still cause interference to each other– Flow2 may have a jitter (traffic model changed in S3)
Because of the contention with Flow1
o This behavior is common in a large multi-hop networko Must be taken into account, otherwise the result may be optimistic
Challenges in guaranteed analysis
• Further issues may cause challenges into the analysis which increases of the complexity of network topologies and traffic modelso Support for arbitrary deadlines
The deadline assumptions can be any value– less, equal or greater then the periods
o Support for non-fragmentation as well as fragmentations Max size per Ethernet frame is 1500 bytes
o May require different formulas for different situations
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• Network system modeling o Switch modeling o Host modelingo Link modeling
• Traffic modelingo Flow modeling
Single and multi frame support
Tasks– Executables in hosts
Desired features and functionalities of a tool
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Desired features and functionalities of a tool
• Computation analysis engine o The engine should generate guaranteed
results without optimism and with limited pessimism
• Network optimization engineo An optimization engine can help the
automotive system designers to optimize the system based on the analysis results
Consider given requirements and constraints– Reaction constraints, age constraints,
synchronization constraints, etc.
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Summary
• The paper discusses the challenges and important considerations for a guaranteed response time analysis over Etherneto But due to the unpredictability of the multi-hop
network behavior it is really difficult to achieve a precise analysis without
doing an exhaustive search for all appropriate traffic scenarios
• A tool designer should consider the balance between the accuracy and the computation timeo Find a proper algorithm that requires a limited
computing resource and still produce accepted results
2012-01-0193