Configuring the communication on FlexRay: the case of the static segment
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The document discusses the complexities of configuring FlexRay communication, particularly for the static segment, and highlights the challenges posed by Autosar constraints and performance requirements. It presents an algorithm for constructing configurations that optimize signal transmission while meeting timing constraints, alongside results from performance evaluations comparing different scheduling strategies. Conclusions emphasize the importance of proper configuration for effective communication in automotive systems and suggest further research on asynchronous tasks and frame packing.
![Case 1 : synchronous case (1/2)
Best possible results with regard to signal latency
and dependability
Picture from [1]
5](https://image.slidesharecdn.com/flexrayerts-111114030130-phpapp01/85/Configuring-the-communication-on-FlexRay-the-case-of-the-static-segment-5-320.jpg)
![References (1/2)
FLEXRAY – protocol and use by carmarkers
[1] B. Schätz, C. Kühnel, M. Gonschorek, “The FlexRay Protocol”, to appear in the
Automotive embedded Handbook, N. Navet, F. Simonot-Lion editors, CRC
Press/Taylor and Francis, 2008.
[2] Vector Informatik GmbH, interview of Mr. Peteratzinger (BMW), Mr. Steiner (BMW),
“Use of XCP on FlexRay at BMW”, published in “Collection of professional articles”,
09/2006. Available at www.vector-worldwide.com/articles
[3] A. Schedl, “Goals and Architecture of FlexRay at BMW”, slides presented at the
Vector FlexRay Symposium, March 6 2007.
[4] J. Broy (Porsche A.G.), K.D. Müller-Glaser, “The impact of time-triggered
communication in automotive embedded systems”, IEEE SIES’2007, July 2007.
FRAME PACKING
[5] R. Saket, N. Navet, "Frame Packing Algorithms for Automotive Applications", Journal
of Embedded Computing, vol. 2, n° 1, pp93-102, 2006.
DEPENDABILITY
[6] B. Gaujal, N. Navet, "Maximizing the Robustness of TDMA Networks with
Applications to TTP/C", Real-Time Systems, Kluwer Academic Publishers, vol 31,
n°1-3, pp5-31, December 2005.
21](https://image.slidesharecdn.com/flexrayerts-111114030130-phpapp01/85/Configuring-the-communication-on-FlexRay-the-case-of-the-static-segment-21-320.jpg)
![References (2/2)
CONFIGURATION OF THE STATIC SEGMENT
[6] S. Ding, N. Murakami, H. Tomiyama, H. Takada, “A GA-based scheduling method for
FlexRay systems”, EMSOFT, 2005.
[7] A. Hamann, R. Ernst, “TDMA Time Slot and Turn Optimization with Evolutionary
Search Techniques”, Proceedings of the Design, Automation and Test in Europe
Conference, Volume 1, p312–317, 2005.
[8] E. Wandeler, L. Thiele, “Optimal TDMA time slot and cycle length allocation for hard
real-time systems”, Proceedings of the 2006 conference on Asia South Pacific
design automation.
[9] M. Grenier, L. Havet, N. Navet, “Configuring the communication on FlexRay: the case
of the static segment”, Proceedings of ERTS’2008.
CONFIGURATION OF THE DYNAMIC SEGMENT
[10] T. Pop, P. Pop, P. Eles, Z. Peng, A. Andrei, “Timing Analysis of the FlexRay
Communication Protocol”, ECRTS 2006.
[11] T. Pop, P. Pop, P. Eles, Z. Peng, “Bus Access Optimisation for FlexRay-based
Distributed Embedded Systems”, DATE 2007.
INTERFERENCE OF SCS TASKS ON FPS TASKS
[12] T. Pop, P. Pop, P. Eles, Z. Peng, “Optimization of Hierarchically Scheduled
Heterogeneous Embedded Systems”, RTCSA’2005.
22](https://image.slidesharecdn.com/flexrayerts-111114030130-phpapp01/85/Configuring-the-communication-on-FlexRay-the-case-of-the-static-segment-22-320.jpg)
Configuring the communication on FlexRay: the case of the static segment
- 1. Configuration the Communication on FlexRay the case of the static segment Nicolas NAVET INRIA / RealTime-at-Work http://www.loria.fr/~nnavet http://www.realtime-at-work.com Nicolas.Navet@loria.fr ERTS – 30/01/2008 Joint work with Mathieu GRENIER and Lionel HAVET
- 2. FlexRay configuration Extremely complex problem: Mixed of TT and ET scheduling Tightly linked with task scheduling Large number of parameters (>70) AUTOSAR constraints (OS, COM, etc) … Design objectives should be first clearly identified: Minimum bandwidth to use cheap components (2.5 Mbit/s, 5MBit/s ?) Enable incremental design ? Carry-over of ECUs ? No chance to solve the pb optimally – too many free variables, sub-problems alone are NP-hard 2
- 3. Requirements on FlexRay Performance requirements: both run-time (response times, jitters, etc.) and End-of-Line/Garage flash update Incrementality requirements: additional functions or ECUs Dependability requirements: fail-silence, babbling idiot, deadline failure probability under EMI, … Platform requirements: platform wide frames (e.g., NM), carry-over of ECUs, able to deal with com. controller + CPU + Autosar stack performances, … 3
- 4. Tasks run either synchronously or asynchronously wrt the communication cycle
- 5. Case 1 : synchronous case (1/2) Best possible results with regard to signal latency and dependability Picture from [1] 5
- 6. Case 1 : synchronous case (2/2) But strong constraints: require Static Cyclic Scheduling impose to re-design existing functions / design according to the bus configuration task periods constrained by FlexRay/Autosar rules (cycle repetition, e.g. 10, 20, 40, 80ms with a cycle=5ms) might require to artificially increase the frequency of some tasks → CPU load length of the communication cycle is crucial 6
- 7. Case 2 : asynchronous case Signals produced at variable time points in the round – depends on the scheduling of tasks Signal Release interval Static segment Dynamic segment Signal freshness constraint imposes a range of slots for transmission and a min. frequency (every x cycles) Scope of the study 7
- 8. Assumptions on FlexRay (1/2) 1. Signals with up to 2.5 ms constraints are transmitted in the ST segment: DYN segment < 2.5ms Here : ST = 3ms, DYN (+NIT+SW) = 2ms 2. Frames data payload = 16 bytes Bit Rate (Mbit/s) 2.5 5 10 gN umberOf StaticSlots 27 51 93 8
- 9. Assumptions on FlexRay (2/2) 3. Only one communication channel is used 4. A signal is produced with given period and offset 5. Deadlines ≤ Periods: no buffer overwrite 6. One signal per frame: no signal multiplexing 7. FlexRay is used in the context of AUTOSAR an AUTOSAR frame is defined by: FRIF_SLOT_ID: static segment slot FRIF_BASE_CYCLE: first transmission cycle FRIF_CYCLE_REPETITION: must be a power of two 9
- 10. Communication schedule Static Segment ECUa ECUb ECUa ECUc … ECUc Cycle 0 FRIF_SLOT_ID: 1 Frame FRIF_BASE_CYCLE: 1 1 FRIF_CYCLE_REPETITION: 2 2 3 Static segment configuration : 4 1) allocation of the slots to the . ECUs . . 2) Defining frame characteristics + signals they carry 63 10
- 11. Timing Constraints: asynchronous case offset 100ms signal 80ms frame Signal age (or signal response time): time between production of a signal and end of transmission of the first frame containing the signal Max signal age = 80ms here 11
- 12. Problems addressed in the paper 1. Check timing constraints : Non-schedulability tests for a set of signals - if non-schedulable is returned then no feasible configuration exists An exact schedulability analysis of a given configuration 2. Algorithm to construct the configuration starting from the set of signals – Objective: minimize the # of slots used while meeting timing constraints 12
- 13. Sketch of the algorithm: “Best Slot First” (BSF) For each slot and each ECU, compute the “maximum” number of signals the slot can transmit: A heuristic is used to build the set of frames for each slot / ECU Keep the slot/ECU choice that maximizes the number of signals transmitted Repeat until there is no signal or no slot left 13
- 14. Performance evaluation Performance metrics: 1. Percentage of feasible signal sets 2. # of slots used in the static segment Benchmark against a naïve strategy called Randomized Slot Selection (RSS)
- 15. Experimental setup 8 bytes signals in 16 bytes frames (no PDU multiplex.) Static segment = 3ms – communication cycle = 5ms 10Mbit/s FlexRay – 93 slots Signals generated with NETCARBENCH Freshness constraints : Case 1: Equal to periods Case 2 : Equal to min( period, 30ms) Available bandwidth (ST seg. alone – “power of two” constraints not considered) ≈ 1.2Mbit/s (out of 6Mbit/s) In our experiments (case 1), 1Mbit/s of data leads to 88 slots on average 15
- 16. Deadlines equal to periods # of feasible signal sets out of 100 signal rate (kbit/s) 250 400 550 700 850 1000 BSF 100 100 100 100 100 100 RSS 96 61 12 0 0 0 # of slots used in the static segment (out of 93) signal rate (kbit/s) 250 400 550 700 850 1000 BSF 25.1 37.3 49.9 65.9 77 88 RSS 89.2 93 93 NA NA NA 16
- 17. Deadlines smaller than periods # of feasible signal sets out of 100 signal rate (kbit/s) 250 400 550 700 850 1000 Test1 100 100 100 100 100 85 Test2 100 100 100 100 35 0 BSF 100 100 100 52 2 0 RSS 96 68 8 0 0 0 850 kbit/s : Test2 says that 35 might be feasible while BSF only find 2 feasible configurations - is test 2 optimistic or BSF inefficient ? 17
- 18. Conclusions / Perspectives Solutions to configure the static segment of FlexRay considering automotive constraints → implemented in a prototype generating FIBEX file Tests help to identify signals that would be best transmitted in the dynamic segment Asynchronous tasks : response times can be larger than on CAN Frame packing is needed – 2 levels: Packing signals into 8-bytes PDU at the AUTOSAR communication level Packing PDUs into frames at the AUTOSAR FlexRay Interface level 18
- 19. Questions, feedback? please contact me at Nicolas.Navet@loria.fr 19
- 20. References
- 21. References (1/2) FLEXRAY – protocol and use by carmarkers [1] B. Schätz, C. Kühnel, M. Gonschorek, “The FlexRay Protocol”, to appear in the Automotive embedded Handbook, N. Navet, F. Simonot-Lion editors, CRC Press/Taylor and Francis, 2008. [2] Vector Informatik GmbH, interview of Mr. Peteratzinger (BMW), Mr. Steiner (BMW), “Use of XCP on FlexRay at BMW”, published in “Collection of professional articles”, 09/2006. Available at www.vector-worldwide.com/articles [3] A. Schedl, “Goals and Architecture of FlexRay at BMW”, slides presented at the Vector FlexRay Symposium, March 6 2007. [4] J. Broy (Porsche A.G.), K.D. Müller-Glaser, “The impact of time-triggered communication in automotive embedded systems”, IEEE SIES’2007, July 2007. FRAME PACKING [5] R. Saket, N. Navet, "Frame Packing Algorithms for Automotive Applications", Journal of Embedded Computing, vol. 2, n° 1, pp93-102, 2006. DEPENDABILITY [6] B. Gaujal, N. Navet, "Maximizing the Robustness of TDMA Networks with Applications to TTP/C", Real-Time Systems, Kluwer Academic Publishers, vol 31, n°1-3, pp5-31, December 2005. 21
- 22. References (2/2) CONFIGURATION OF THE STATIC SEGMENT [6] S. Ding, N. Murakami, H. Tomiyama, H. Takada, “A GA-based scheduling method for FlexRay systems”, EMSOFT, 2005. [7] A. Hamann, R. Ernst, “TDMA Time Slot and Turn Optimization with Evolutionary Search Techniques”, Proceedings of the Design, Automation and Test in Europe Conference, Volume 1, p312–317, 2005. [8] E. Wandeler, L. Thiele, “Optimal TDMA time slot and cycle length allocation for hard real-time systems”, Proceedings of the 2006 conference on Asia South Pacific design automation. [9] M. Grenier, L. Havet, N. Navet, “Configuring the communication on FlexRay: the case of the static segment”, Proceedings of ERTS’2008. CONFIGURATION OF THE DYNAMIC SEGMENT [10] T. Pop, P. Pop, P. Eles, Z. Peng, A. Andrei, “Timing Analysis of the FlexRay Communication Protocol”, ECRTS 2006. [11] T. Pop, P. Pop, P. Eles, Z. Peng, “Bus Access Optimisation for FlexRay-based Distributed Embedded Systems”, DATE 2007. INTERFERENCE OF SCS TASKS ON FPS TASKS [12] T. Pop, P. Pop, P. Eles, Z. Peng, “Optimization of Hierarchically Scheduled Heterogeneous Embedded Systems”, RTCSA’2005. 22