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Flexibility and Dependability in In-Vehicle Communication: Analysis of Message Scheduling Systems

This presentation discusses the flexibility and dependability of in-vehicle communication systems, specifically focusing on periodic message sets and scheduling methodologies such as TDMA and CAN. It provides examples of scenarios with different network load conditions, highlighting message transmission rates and results under various circumstances. The analysis delves into reliability concepts, including fault tolerance and error correction, demonstrating how structured communication schedules contribute to predictable and reliable vehicle networking. The findings emphasize the significance of a well-designed communication framework for automotive systems.

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Flexibility and Dependability in In-Vehicle Communication: Analysis of Message Scheduling Systems

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  1. In-Vehicle Communication SAN Group RTS Regular Meeting Presentation December 2008

  2. FLEXIBILITY • A simple example of a periodic message set (a low network load of nearly 35%) br = 250 kbps CM = 125 x (4x10-3) = 0.5 msec

  3. N1 N2 N3 N4 N5 TDMA Round 2.5 0 msec TTP/C Scheduling • The respective time-triggered schedule for the message set can be constructed as follows • TDMA rounds (here 1 TDMA round) form the cluster cycle that repeats itself t

  4. All M3 M2 M1 M2 M1 M2 M3 M4 M5 2.5 0.5 1.0 1.5 2.0 0 5.0 3.0 3.5 4.0 4.5 2.5 M1, M4 and M5 Rt (M2’’) = 2.5 Rt (M3’’) = 1 Rt (M2’’’) = 1.5 Rt (M1) = 0.5 Rt (M4) = 2 Rt (M5) = 2.5 0.5 N/w load = 35 % BU = 40 % M1 7.5 5.5 6.0 6.5 7.0 5.0 M2 M3 10.0 8.0 8.5 9.0 9.5 7.5 M1 M4 M5 12.5 10.5 11.0 11.5 12.0 10.0

  5. M3 M2 M2 M1 CAN Scheduling • Scheduling is based on FPNS • Unique priority for each message (lower id. means higher priority M1, M4 and M5 t (msec) …. M3 M1 M4 M5 M2 M1 M2 …. …. 9.5 10.0 10.5 11.0 11.5 12.0 12.5 0 5.0 5.5 6.0 6.5 8.0 8.5 9.0 Rt (M2’’) = 0.5 Rt (M3’’) = 0.5 Rt (M2’’’) = 0.5 Rt (M1) = 0.5 Rt (M4) = 1 Rt (M5) = 1.5 TT Results Rt (M2’’) = 2.5 Rt (M3’’) = 1 Rt (M2’’’) = 1.5 Rt (M1) = 0.5 Rt (M4) = 2 Rt (M5) = 2.5 N/w load = 35 % BU = 41 %

  6. A further example of a periodic message set (an average network load of nearly 50%) br = 250 kbps CM = 125 x (4x10-3) = 0.5 msec

  7. N1 (M1) N2 (M2) N3 (M3) N4 (M4) N5 (M5) N1 (M6) N2 (M7) N3 (M8) N4 (M9) N5 (M10) 2.5 0 5.0 t TTP/C Scheduling Cluster Cycle TDMA Round #1 TDMA Round #2

  8. All M1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 M1 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 M1 M3 M1 M1 M3 M2 M2 Node 1: M1, M6 Node 2: M2, M7 Node 3: M3, M8 Node 4: M4, M9 Node 5: M5, M10 M1, M4-7 M2 M3 Rt (M2’’) = 2.5 Rt (M3’’) = 1 Rt (M2’’’) = 1.5 Rt (M4’’) = 2 Rt (M5’’) = 2.5 Rt (M6’’) = 3 Rt (M7’’) = 1 Rt (M8’’) = 1,5 M1 M7 M4 M5 M6 M2 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 M2 M1, M4-7, M8 M1 M3 M2 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 M2, M3 N/w load = 50 % BU = 60 % M1 M8 M4 M5 M7 M6 M7 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 M2 M3 M1 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0

  9. CAN Scheduling Rt (M2’’) = 0.5 Rt (M3’’) = 0.5 Rt (M2’’’) = 0.5 Rt (M4’’) = 1 Rt (M5’’) = 1.5 Rt (M6’’) = 2 Rt (M7’’) = 3 Rt (M8’’) = 3 TT Results Rt (M2’’) = 2.5 Rt (M3’’) = 1 Rt (M2’’’) = 1.5 Rt (M4’’) = 2 Rt (M5’’) = 2.5 Rt (M6’’) = 3 Rt (M7’’) = 1 Rt (M8’’) = 1,5 N/w load = 50 % BU = 63 %

  10. A further example of a periodic message set (a high network load of nearly 85%) br = 250 kbps CM = 125 x (4x10-3) = 0.5 msec

  11. N1 (M1) N2 (M2) N3 (M3) N4 (M4) N5 (M5) N1 (M6) N2 (M7) N3 (M8) N4 (M9) N5 (M10) 2.5 0 5.0 t TTP/C Scheduling Cluster Cycle TDMA Round #1 TDMA Round #2

  12. All M1-6 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 M1 M2 M3 M4 M5 M6 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 M7 M1-6 M7 M8 M1-6, M7, M9-10 M8 M1-6 Node 1: M1, M6 Node 2: M2, M7 Node 3: M3, M8 Node 4: M4, M9 Node 5: M5, M10 M1-6, M9-10 Rt (M2’’) = 1 Rt (M3’’) = 1.5 Rt (M4’’’) = 2 Rt (M5’’) = 2.5 Rt (M6’’) = 3 Rt (M7’’) = 2.5 Rt (M8’’) = 1 Rt (M9’’) = 4.5 Rt (M10’’) = 5 Rt (M7’’’) = 1.5 Rt (M8’’’) = 3 Rt (M9’’’) = 4.5 Rt (M10’’’) = 5 Rt (M74) = 4.5 Rt (M84) = 5 M7 M8 M1 M2 M3 M4 M5 M6 M7 M9 M10 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 M7 M1-6, M9-10 M1 M2 M3 M4 M5 M7 M6 M8 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 M7, M8 M1 M3 M4 M5 M2 M6 M9 M10 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 N/w load = 85 % BU = 88 % M2 M3 M1 M4 M5 M6 M7 M8 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0

  13. CAN Scheduling TT Results Rt (M9’’) = 4.5 Rt (M10’’) = 5 Rt (M9’’’) = 4.5 Rt (M10’’’) = 5 Rt (M74) = 4.5 Rt (M84) = 5 Rt(M9’’) = 4 Rt (M10’’) = 4.5 Rt (M9’’’) = 3.5 Rt(M10’’’) = 4 Rt (M74) = 0.5 Rt (M84) = 1 N/w load = 85 % BU = 91 %

  14. DEPENDABILITY • dependability = predictability + reliability • Predictable: Time-triggered manner, Predefined communication schedule • Reliability: fault confinement and fault tolerance (a fault does not reveal an error in the system)

  15. DEPENDABILITY • Let us suppose that retransmissions occur for M1 (2), M2 (3), and M5 (2) as a result of some fault (faulty message) starting from the time 5 msec on the high load CAN network, • Error recovery time ~ 17-31 bits • Result in messages M6 and M7 miss their deadlines • CRC, retransmission and error counter • Very difficult to solve the problem • “Babbling idiot” fault • The node has to diagnose itself

  16. For the TT network, • Retransmission is not allowed • No deadline miss for other messages • Because of predictability, easy to define and solve the problem • Replicated communication channels and nodes • CRC • Error handling strategy (fail silence and restart after a self test) • Fault confinement mechanisms: • Bus guardian • Membership functions • Clique avoidance algorithm • Error Containment (control and data errors) • CNI acts as control error containment boundaries • For data errors, High Error Detection Coverage Mode (HEDC) provides two mechanisms, • end-to-end CRC calculation by application task (two CRC calculations) • Time redundant execution of application tasks at the sender

  17. COMPOSABILITY • For TT network • Communication not depending on host controller and application software in it since • System integration does not change temporal behavior • Thus composable w.r.t. temporal properties • For CAN network • Temporal behavior is dependent on host controller

  18. EXTENSIBILITY • For the TT network, difficult to add new nodes and messages • Construction of new schedule (TDMA rounds that form cluster cycle) • Construction of Message Descriptor List (MEDL) • For CAN network it is an easy process, • Update for message priorities

  19. In-vehicle Systems’ Requirements* * T. Nolte, “Share-driven scheduling of embedded networks”, Doctoral dissertation No. 26, Mälardalen University, Sweden, 2006.

  20. INITIAL RESEARCH QUESTIONS • Integration, coherence and interoperability of different in-vehicle networks in a car • What makes FlexRay as a strongest candidate for in-vehicle networks instead of CAN? • Schedule construction • Fault tolerance • Performance analysis and comparison • Any possible improvement • Reservation based approaches for event-triggered traffic of hybrid communication networks

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