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On the Quantification of Sustainability and Extensibility of FlexRay Schedules

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

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On the Quantification of Sustainability and Extensibility of FlexRay Schedules

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  1. On the Quantification of Sustainabilityand Extensibility of FlexRay Schedules Reinhard Schneider, Dip Goswami, SamarjitChakraborty TU Munich, Germany UnmeshBordoloi, PetruEles, ZeboPeng Linkoeping University, Sweden DAC’2011, San Diego, US, June 5-10, 2011

  2. Automotive Design Process Protocol configuration Physicallayerconfiguration Initial design phase + Incrementalscheduling ? Update Scheduling FlexRay Network New applicationsat each design cycle Existingschedules ? • Will deadlinesofexistingmessagesbemet in presenceoffuturemessages? • Are enoughsuitableschedulesavailabletoaccomodatefuturemessages? • Howtoquantify and interpretatesustainable and extensible schedules? • Howtocapture all FlexRay-specificproperties in an analysisframework?

  3. FlexRay Protocol dynamic static minislots pLatestTx=6 cycles 1 2 3 4 5 6 7 8 63 • Communication isorganized in a periodicesequenceofbuscycles • Static (time-triggered) anddynamic (event-triggered) segments • Staticslotsdenote time windowsoffixedandequallength • Dynamicslotsarelogicalentitieswhichspecifyprioritiesandcompriseofseveralminislotsdepending on themessagesizes m4 62 • Transmissionpointsof miareuniquelyspecifiedbythetuple and S1 = 7 displaced m3 . . . . 5 . . R1 = 2 m4 4 m1 m3 3 Examples: m4 2 1 B1 = 1 m2 m2 m4 0 slots 1 2 3 4 5 S1 = 6 Latestminislot totransmit m3 Staticslots

  4. Sustainability Analysis a) Deadline d3of m3is still met in presenceof m6? cycle Workloadestimation Severalpayloadsizes n result in a constant minislotconsumption f(n) on thebus m1 63 b) Sufficient minislotsavailable totransmit m3? m2 m3 62 FromtheFlexRayspecification B.4.14 [13]: Temporal isolationbetweenslots in thestaticsegment Interferenceofmessageswith higherpriorities in thedynamicsegment m1 5 . . Intuitive idea: e.g., f(n)=3 . m2 m3 m4 4 n1=6 bytes n1 m1 3 bus n2=8 bytes n2 m2 c) Howtoestimatetheworkload offuturemessages? m3 2 bus m1 1 n3 n3=10 bytes m2 m3 m4 0 bus Sustainabilitytest: m5 m5 m5 m5 1 2 3 4 5 slot Design cycleI m6 m5 Design cycleI+1 m6 m7 m7

  5. Extensibility Analysis a) Howtomeasureextensibilityfor a particularslot? cycle • Quality ratingfunction P1(Si): • Abilityof a slot Sitoprovide • real-time guarantees (priorities) m1 63 m2 m3 62 • b) Slotsmightbereservedforspecialfunctionalities • Onlyparticular • cyclesavailable • Emptyslot • Grade ofextensibility P2(Si): • Abilityof a slottoprovide • versatile schedulesto • accomodatefuturemessages m1 5 . . . m2 m3 m4 4 m1 3 m2 m3 2 • c) Howtoquantify • prioritiesofslots m1 1 m2 m3 m4 0 1 2 3 4 5 6

  6. Extensibility Index • HolisticquantificationofextensibilityforFlexRaynetworksthatdependson both, the Grade ofExtensibilityandtheQuality Rating • Benefits: • OnlyonemetricnecessarytoquantifyandcomparetheextensibilityofFlexRaynetworks • Easy visualizationandinterpretation • Applicabletostaticanddynamicsegments

  7. Experimental Results • µ10 = 167 • pLatestTx = 237 d10 = 22ms D10 = 11,30ms • Visualizationoftheextensibilityindex • Quality ratingfunction • 4 minislotsconsideredforfuturemessages, i.e., payload 22 – 38 bytes In future: µ10 = 317 > 237 • µ94 = 152 • pLatestTx = 237 d94 = 22ms D94 = 21,56ms Fullavailablestaticslots Fullavailabledynamicslots withhighpriorities Onlysomeschedules withhighprioritiesavailable • In future: D94 = 22,76 ms > 22ms emptyslots: E(Si)=P1(Si) • Bothmessages, m10and m94meettheir • constraintsnow (atcurrent design iteration) but • do not pass thesustainabilitytest Unavailabledynamicslots withhighpriorities Unavailablestaticslots completelyfilledslots: E(Si)=0

  8. ConcludingRemarks • Notion ofsustainabilityandextensibility in thecontextofFlexRay • Presentedanalysisframeworkreflects all protocoldetails • Easy visualizationandinterpretation • Future workenvisagestoautomaticallysynthesizesustainableand extensible schedules More detailsavailableatthepostersession

  9. Backup for Q&A

  10. Grade ofExtensibility • Thereare 127 choicestoschedule a message mi in slot Si cycle cycle 63 63 62 62 5 5 . . . . . . . . . 4 4 3 2 . 1 1 . . . . 0 0 Si 1 2 3 4 5 6 7 8 9 49,6% of all schedulesareavailableforfuturemessages in slot 3 • 49,6% of all schedulesareavailableforfuturemessages in slot 9 24,4% of all schedulesareavailableforfuturemessages in slot 6 Noschedulesareavailableforfuturemessages in slot 7 All schedulesareavailableforfuturemessages in slot 8 slot .

  11. Quality Rating Function Example: k Reservedslotsare not considered in theextensibilityanalysis, P1(Si)=0 • Staticslotsareconsideredwithhighestpriority, P1(Si)=1 • Dynamic slotsareconsideredwithdecreasingpriorities, P1(Si) 0 as Si  258

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