1. Technische Universität München On the Quantification of Sustainability and Extensibility of FlexRay Schedules Reinhard Schneider, Dip Goswami, Samarjit Chakraborty TU Munich, Germany DAC’2011, San Diego, US, June 5-10, 2011 Unmesh Bordoloi, Petru Eles, Zebo Peng Linkoeping University, Sweden

2. Technische Universität München Automotive Design Process 2 Protocol configuration Initial design phase FlexRay Network Incremental scheduling New applications at each design cycle Scheduling Update Existing schedules + Physical layer configuration  Will deadlines of existing messages be met in presence of future messages?  Are enough suitable schedules available to accomodate future messages?  How to quantify and interpretate sustainable and extensible schedules?  How to capture all FlexRay-specific properties in an analysis framework?  Will deadlines of existing messages be met in presence of future messages?  Are enough suitable schedules available to accomodate future messages?  How to quantify and interpretate sustainable and extensible schedules?  How to capture all FlexRay-specific properties in an analysis framework? ? ?

3. Technische Universität München 1 Latest minislot to transmit m 3 B 1 = 1 R 1 = 2 S 1 = 6 FlexRay Protocol 3..... cycles 1 2 3 4 5 slots 0 2 4 62..... m1m1  Transmission points of m i are uniquely specified by the tuple S 1 = 7 1 2 3 4 5 6 7 8 m3m3 m3m3 pLatestTx=6 displaced m2m2 m2m2  Communication is organized in a periodice sequence of bus cycles  Static (time-triggered) and dynamic (event-triggered) segments  Static slots denote time windows of fixed and equal length  Dynamic slots are logical entities which specify priorities and comprise of several minislots depending on the message sizes static dynamic Static slots minislots 63 3 5 and m4m4 m4m4 m4m4 m4m4 Examples:

4. Technische Universität München a) Deadline d 3 of m 3 is still met in presence of m 6 ? a) Deadline d 3 of m 3 is still met in presence of m 6 ? cycle slot 0 1 2 3 4 5 62 63..... m1m1 m1m1 m1m1 m1m1 m2m2 m2m2 m2m2 m3m3 m3m3 m3m3 m4m4 m4m4 4 m6m6 Design cycle I+1 m5m5 m2m2 m3m3 m6m6 Sustainability Analysis 1 2 3 4 5 m7m7 m7m7 c) How to estimate the workload of future messages? c) How to estimate the workload of future messages? b) Sufficient minislots available to transmit m 3 ? b) Sufficient minislots available to transmit m 3 ? m5m5 m5m5 m5m5 m5m5 Workload estimation bus Intuitive idea: e.g., f(n)=3 n1n1 bus n2n2 n3n3 n 1 =6 bytes n 2 =8 bytes n 3 =10 bytes Several payload sizes n result in a constant minislot consumption f(n) on the bus From the FlexRay specification B.4.14 [13]: Temporal isolation between slots in the static segment Interference of messages with higher priorities in the dynamic segment Interference of messages with higher priorities in the dynamic segment Design cycle I Sustainability test:

5. Technische Universität München 5 1 2 3 4 5 6 cycle 0 1 2 3 4 5 62 63..... m1m1 m1m1 m1m1 m1m1 m2m2 m2m2 m2m2 m2m2 m3m3 m3m3 m3m3 m3m3 b) Slots might be reserved for special functionalities Extensibility Analysis m4m4 m4m4  Quality rating function P 1 (S i ): Ability of a slot S i to provide real-time guarantees (priorities)  Grade of extensibility P 2 (S i ): Ability of a slot to provide versatile schedules to accomodate future messages a) How to measure extensibility for a particular slot? Empty slot Only particular cycles available Only particular cycles available c) How to quantify priorities of slots c) How to quantify priorities of slots

6. Technische Universität München Extensibility Index 6 Holistic quantification of extensibility for FlexRay networks that depends on both, the Grade of Extensibility and the Quality Rating Benefits:  Only one metric necessary to quantify and compare the extensibility of FlexRay networks  Easy visualization and interpretation  Applicable to static and dynamic segments

7. Technische Universität München Experimental Results 7  Visualization of the extensibility index  Quality rating function  4 minislots considered for future messages, i.e., payload 22 – 38 bytes d 10 = 22ms D 10 = 11,30ms In future: µ 10 = 317 > 237 µ 10 = 167 pLatestTx = 237 d 94 = 22ms D 94 = 21,56ms µ 94 = 152 pLatestTx = 237 In future: D 94 = 22,76 ms > 22ms empty slots: E(S i )=P 1 (S i ) completely filled slots: E(S i )=0 Both messages, m 10 and m 94 meet their constraints now (at current design iteration) but do not pass the sustainability test Both messages, m 10 and m 94 meet their constraints now (at current design iteration) but do not pass the sustainability test Full available static slots Unavailable static slots Full available dynamic slots with high priorities Full available dynamic slots with high priorities Unavailable dynamic slots with high priorities Unavailable dynamic slots with high priorities Only some schedules with high priorities available Only some schedules with high priorities available

8. Technische Universität München Concluding Remarks 8  Notion of sustainability and extensibility in the context of FlexRay  Presented analysis framework reflects all protocol details  Easy visualization and interpretation  Future work envisages to automatically synthesize sustainable and extensible schedules More details available at the poster session

9. Technische Universität München Backup for Q&A 9

10. Technische Universität München Grade of Extensibility 10..... 1 2 3 4 5 6 7 8 9 SiSi 2 3 49,6% of all schedules are available for future messages in slot 3 24,4% of all schedules are available for future messages in slot 6 No schedules are available for future messages in slot 7 All schedules are available for future messages in slot 8 49,6% of all schedules are available for future messages in slot 9 There are 127 choices to schedule a message m i in slot S i 1 0 slot... cycle 4 5 62 63........ cycle 1 0 4 5 62 63.....

11. Technische Universität München Quality Rating Function 11 k Example: Reserved slots are not considered in the extensibility analysis, P 1 (S i )=0 Static slots are considered with highest priority, P 1 (S i )=1 Dynamic slots are considered with decreasing priorities, P 1 (S i )  0 as S i  258