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Flexray

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This presentation is the result of my team in the course "Embedded Systems" at the University of Massachusetts, Amherst. It presents the findings of the paper "Timing analysis of the FlexRay communication protocol", a communication network with automotive uses.

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Flexray

  1. 1. 1 TIMING ANALYSIS OF THE FLEXRAY COMMUNICATION PROTOCOL presented by: CHENG SUN // YINGLAI YANG // YUNNING LI TRAIAN POP, PAUL POP, PETRU ELES, ZEBO PENG, ALEXANDRU ANDREI
  2. 2. 2 Developments in automotive  Comfort: • x-by-wire (drive-by-wire, brake-by-wire, …) • Lane control  Safety: • Automatic emergency brake • Pedestrian recognition  Future: • Self-driving cars CHENG SUN // YINGLAI YANG // YUNNING LI
  3. 3. 3 Realized by distributed systems CHENG SUN // YINGLAI YANG // YUNNING LI
  4. 4. 4 New solution: FlexRay  We need fast, deterministic (safe) communication protocol: Development started at BMW and continued by a consortium resulted in FlexRay protocol.  CAN, LIN vs. FlexRay Bus LIN CAN FlexRay Speed 40 kbit/s 1 Mbit/s 10 Mbit/s Cost $ $$ $$$ Wires 1 2 2 or 4 Typical Applications Body Electronics Powertrain Safety-critical apps CHENG SUN // YINGLAI YANG // YUNNING LI
  5. 5. 5 The FlexRay Protocol  The overview of the system CHENG SUN // YINGLAI YANG // YUNNING LI
  6. 6. 6 The FlexRay Protocol  Detailed information of cycles CHENG SUN // YINGLAI YANG // YUNNING LI
  7. 7. 7 Internal architecture of a node  CPU: writes messages into...  CHI: reserves a buffer...  Controller: reads messages from...  Black Chunk: ~Static  Grey Chunk: ~Dynamic CHENG SUN // YINGLAI YANG // YUNNING LI
  8. 8. 8 Internal architecture of a node The number of slots in ST is fixed,… The size of each slot is fixed,… CHENG SUN // YINGLAI YANG // YUNNING LI
  9. 9. 9 Delays in dynamic segment  (1) Delays by higher priority messages. Here mg and mf share the same Frame ID, but ... CHENG SUN // YINGLAI YANG // YUNNING LI
  10. 10. 10 (1)Delays by higher priority messages  Here mg is delayed by mf . CHENG SUN // YINGLAI YANG // YUNNING LI
  11. 11. 11 Delays in the dynamic segment  (2)Delays by earlier (lower frame) messages and without enough slots left. Such as mh, static segment; Frame ID=5; Assuming that the length of mh takes 2 slots CHENG SUN // YINGLAI YANG // YUNNING LI
  12. 12. 12 (2)Delays by earlier (lower FrameID) messages and without enough slots left.  We can not be too stingy to mh ! CHENG SUN // YINGLAI YANG // YUNNING LI
  13. 13. 13 (2)Delays by earlier (lower FrameID) messages and without enough slots left.  Finally, mh finds an available position.  Although…  What if mg … CHENG SUN // YINGLAI YANG // YUNNING LI
  14. 14. 14 Timing analysis Question for safety issue: How long can it take until a message reaches its recipient? “The driver turns the steering wheel to the left. How long does it maximally take until the car follows that movement?” Value of interest: Worst Response Time – Longest possible time from creation of message to complete arrival. CHENG SUN // YINGLAI YANG // YUNNING LI
  15. 15. 15 Quantization of delay-causes Note: Assume regular, periodic messages with period T (dynamic messages) Such a message will occur 𝑡+𝐽 𝑇 times in the time frame 𝑡. E.g. ℎ𝑝 𝑡 = 𝑡+𝐽ℎ𝑝 𝑇ℎ𝑝 for higher priority messages J is the jitter of the message → difference between best response time to worst response time CHENG SUN // YINGLAI YANG // YUNNING LI
  16. 16. 16 Definition of response time Important for us: Those are the only things that can change. CHENG SUN // YINGLAI YANG // YUNNING LI
  17. 17. 17 Mathematical formulation for 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚 Make it an ILP problem: Furthermore constraints are added to the ILP formulation to satisfy the FlexRay protocol … frame overfilled: 𝑦𝑖 = 1 frame can take message: 𝑦𝑖 = 0 CHENG SUN // YINGLAI YANG // YUNNING LI
  18. 18. 18 Messages are not sent multiple times per cycle CHENG SUN // YINGLAI YANG // YUNNING LI
  19. 19. 19 FrameIDs are unique Or: „You shall not use the same 𝑓𝑟𝑎𝑚𝑒𝐼𝐷 multiple times in one cycle“ CHENG SUN // YINGLAI YANG // YUNNING LI
  20. 20. 20 Fixed assignment of frameID Or: „A message can only be transmitted with the 𝑓𝑟𝑎𝑚𝑒𝐼𝐷 that was assigned to it“ CHENG SUN // YINGLAI YANG // YUNNING LI
  21. 21. 21 Messages need to fit completely Or: „Any message can only be sent if it fits in the remaining space.“ CHENG SUN // YINGLAI YANG // YUNNING LI
  22. 22. 22 Optimal solution for 𝑤 𝑚 ′ After 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚 is known, we maximize the delay in the cycle where the message 𝑚 is being sent (inserted in the dynamic frame). ILP is used again and the max. 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚 is being enforced. The optimization goal is now to find the largest possible 𝑤 𝑚 ′ . Same constraints as before (FlexRay compliance) CHENG SUN // YINGLAI YANG // YUNNING LI
  23. 23. 23 Summary of optimal calculation  ILP used  „Optimization“ goal: Maximize 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚 and 𝑤 𝑚 ′  Constraints used to model FlexRay rules However:  ILP is very computationally complex. Takes extremely long and can exceed available computational power easily! CHENG SUN // YINGLAI YANG // YUNNING LI
  24. 24. 24 Heuristic Solution for 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚 & 𝑤 𝑚 ′ Simplification of calculation of 𝐵𝑢𝑠𝐶𝑦𝑐𝑙𝑒𝑠 𝑚: Straightforward computation of 𝑤 𝑚 ′ : CHENG SUN // YINGLAI YANG // YUNNING LI by adding pessimistic 𝑚𝑠-count to communication time:
  25. 25. 25 Experimental Setup CHENG SUN // YINGLAI YANG // YUNNING LI OO- is not used in production since it is optimistic about WRT. It is only used to be able to calculate a common reference value for OH and HH.
  26. 26. 26 Experimental Results Where A presents OO, OH or HH, and n is the number of messages in the analyzed application. CHENG SUN // YINGLAI YANG // YUNNING LI
  27. 27. 27 Experimental Results CHENG SUN // YINGLAI YANG // YUNNING LI Fewer frameIDs/processor → constraints more important → heuristics worse
  28. 28. 28 Conclusions  The paper showed a way to analyze the worst response time.  It was shown how heuristics can be used to radically reduce the calculation time of the WRT with a trade off in additional pessimism of the result.  Allows timing assertions for safety analysis.  First paper to analyze dynamic FlexRay timing without simplifying constraints.  Good heuristics with very low calculation time. CHENG SUN // YINGLAI YANG // YUNNING LI
  29. 29. 29 CHENG SUN // YINGLAI YANG // YUNNING LI Thank you for your attention!
  30. 30. 30 Q&A CHENG SUN // YINGLAI YANG // YUNNING LI

This presentation is the result of my team in the course "Embedded Systems" at the University of Massachusetts, Amherst. It presents the findings of the paper "Timing analysis of the FlexRay communication protocol", a communication network with automotive uses.

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