Synthesis of Communication Schedules for TTEthernet-based Mixed-Criticality Systems Domițian Tămaș-Selicean 1, Paul Pop 1 and Wilfried Steiner 2 1 Technical.

Synthesis of Communication Schedules for TTEthernet-based Mixed-Criticality Systems Domițian Tămaș-Selicean 1, Paul Pop 1 and Wilfried Steiner 2 1 Technical University of Denmark 2 TTTech Computertechnik AG

2 Outline  Motivation  TTEthernet  ARINC 664p7 “Aircraft Data Network”  TT and RC Traffic Transmission  Problem Formulation  Motivational Example  Optimization Strategy  RC End-to-End Analysis  Experimental results  Conclusions

3 Point-to-point connection Motivation  Real time applications implemented using distributed systems PE Application A 1 -- highly critical Application A 2 -- critical Application A 3 -- non-critical Bus connection  Reduces wiring and weight  Mixed-criticality applications share the same network

4 ARINC 664 p7 “Aircraft Data Network” ES 1 ES 2 NS 1 NS 2 ES 3 ES 4  Full-Duplex Ethernet-based data network for safety-critical applications End System Network Switch

5 ARINC 664 p7 “Aircraft Data Network” ES 1 ES 2 NS 1 NS 2 ES 3 ES 4 CPU RAM ROM NIC

6 ARINC 664 p7 “Aircraft Data Network” ES 1 ES 2 NS 1 NS 2 ES 3 ES 4 NS 1 to ES 1 ES 1 to NS 1 dataflow link

7 ARINC 664 p7 “Aircraft Data Network” NS 1 NS 2 vl 2 vl 1 ES 1 τ1τ1 ES 2 τ4τ4 ES 3 τ2τ2 τ5τ5 ES 4 τ3τ3  Highly critical application A 1 : τ 1, τ 2 and τ 3  τ 1 sends message m 1 to τ 2 and τ 3  Non-critical application A 2 : τ 4 and τ 5  τ 4 sends message m 2 to τ 5 virtual link

8 ARINC 664 p7 “Aircraft Data Network” NS 1 NS 2 dp 1 vl 1 dp 2 l1l1 l2l2 l3l3 l4l4 ES 1 τ1τ1 ES 2 τ4τ4 ES 3 τ2τ2 τ5τ5 ES 4 τ3τ3 dataflow path  Highly critical application A 1 : τ 1, τ 2 and τ 3  τ 1 sends message m 1 to τ 2 and τ 3  Non-critical application A 2 : τ 4 and τ 5  τ 4 sends message m 2 to τ 5

9 ARINC 664 p7 “Aircraft Data Network”  Deterministic Event Triggered communication  Separation of traffic enforced through “bandwidth allocation”  Bandwidth Allocation Gap (BAG) – minimum time interval between two consecutive instances of a frame on a virtual link f x,1 f x,2 BAG x  Maximum bandwidth assigned to virtual link vl i BW (vl i ) = f i.size/BAG i

10 TTEthernet  ARINC 664p7 compliant  Traffic classes:  synchronized communication  Time Triggered (TT)  unsynchronized communication  Rate Constrained (RC) – ARINC 664p7 traffic class  Best Effort (BE) – no timing guarantees  Standardized as SAE AS 6802  Marketed by TTTech Computertechnik AG  Implemented by Honeywell on the NASA Orion Constellation

11 TTEthernet  Composed of clusters  Each cluster has a clock synchronization domain  Inter-cluster communication using RC traffic ES 1 ES 2 NS 1 ES 3 ES 4 ES 5 ES 6 NS 2 ES 7 ES 8 Cluster 1 Cluster 2

12 b TT Transmission CPU P 1,1 τ1τ1 P 1,2 τ2τ2 B 2,Tx B 1,Tx TT S P 1,3 P 2,1 τ4τ4 P 2,2 τ3τ3 P 2,3 CPU FU B 1,Rx B 2,Rx ES 1 ES 2 NS 2 NS 3 FU TT R B 1,Tx B 2,Tx TT S NS 1 S f2f2 f3f3 f4f4 TT a c d e f g h i j k l m SRSRS A 1 : τ 1   m 1  τ 3, RC A 2 : τ 2   m 2  τ 4, TT b

13 b b TT Transmission CPU P 1,1 τ1τ1 P 1,2 τ2τ2 B 2,Tx B 1,Tx TT S P 1,3 P 2,1 τ4τ4 P 2,2 τ3τ3 P 2,3 CPU FU B 1,Rx B 2,Rx ES 1 ES 2 NS 2 NS 3 FU TT R B 1,Tx B 2,Tx TT S NS 1 S f2f2 f3f3 f4f4 TT a c d e f g h i j k l m SRSRS A 1 : τ 1   m 1  τ 3, RC A 2 : τ 2   m 2  τ 4, TT a c d e f g h i j k l m Packing message m 2 into frame f 2 Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S TT S sends f 2 to NS 1 f 2 is sent on the dataflow link to NS 1 The Filtering Unit (FU) checks the frame f 2 Expected receive time specified in receive schedule S R TT R checks if f 2 arrives according to schedule Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S FU checks f 2 Store the frame into receive buffer B 2,Rx Task τ 4 reads f 2 from buffer b

19 b b TT Transmission CPU P 1,1 τ1τ1 P 1,2 τ2τ2 B 2,Tx B 1,Tx TT S P 1,3 P 2,1 τ4τ4 P 2,2 τ3τ3 P 2,3 CPU FU B 1,Rx B 2,Rx ES 1 ES 2 NS 2 NS 3 FU TT R B 1,Tx B 2,Tx TT S NS 1 S f2f2 f3f3 f4f4 TT a c d e f g h i j k l m SRSR S A 1 : τ 1   m 1  τ 3, RC A 2 : τ 2   m 2  τ 4, TT a c d e f g h i j k l m Packing message m 2 into frame f 2 Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S TT S sends f 2 to NS 1 f 2 is sent on the dataflow link to NS 1 The Filtering Unit (FU) checks the frame f 2 Expected receive time specified in receive schedule S R TT R checks if f 2 arrives according to schedule Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S FU checks f 2 Store the frame into receive buffer B 2,Rx Task τ 4 reads f 2 from buffer b

22 b b TT Transmission CPU P 1,1 τ1τ1 P 1,2 τ2τ2 B 2,Tx B 1,Tx TT S P 1,3 P 2,1 τ4τ4 P 2,2 τ3τ3 P 2,3 CPU FU B 1,Rx B 2,Rx ES 1 ES 2 NS 2 NS 3 FU TT R B 1,Tx B 2,Tx TT S NS 1 S f2f2 f3f3 f4f4 TT a c d e f g h i j k l m SRSR S A 1 : τ 1   m 1  τ 3, RC A 2 : τ 2   m 2  τ 4, TT a c d e f g h i j k l m Packing message m 2 into frame f 2 Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S TT S sends f 2 to NS 1 f 2 is sent on the dataflow link to NS 1 The Filtering Unit (FU) checks the frame f 2 Expected receive time specified in receive schedule S R TT R checks if f 2 arrives according to schedule Place f 2 in buffer B 1,Tx for transmission Send time specified in send schedule S S FU checks f 2 Store the frame into receive buffer B 2,Rx Task τ 4 reads f 2 from buffer b

26 RC Transmission CPU P 1,1 τ1τ1 P 1,2 τ2τ2 Q 1,Tx Q 2,Tx B 2,Tx B 1,Tx TR 2 TR 1 RC S TT S P 1,3 P 2,1 τ4τ4 P 2,2 τ3τ3 P 2,3 CPU FU Q 1,Rx Q 2,Rx B 1,Rx B 2,Rx ES 1 ES 2 NS 2 NS 3 FU TP TT R B 1,Tx B 2,Tx TT S NS 1 S f2f2 f3f3 f4f4 f1f1 RC TT Q Tx 1 23 4 5 6 7 89 1010 1 1212 1313 SRSRS 1 Packing message m 1 into frame f 1 2 Insert it in queue Q 1,Tx 3 Traffic Regulator (TR) ensures bandwidth for each VL 4 RC scheduler RC multiplexes frames coming from TRs 5 TT S transmits f 1 when there is no TT traffic 6 f 1 is sent on the dataflow link to NS 1 7 FU checks the validity of the frame 8 Traffic Policing (TP) checks that f2 arrives according to the BAG 9 Copy f 1 to outgoing queue Q Tx 1010 Send f 1 when there is no TT traffic 1 FU checks f 1 1212 Copy to receiving Q 2,Rx 1313 Task τ 3 reads f 1 from the queue A 1 : τ 1   m 1  τ 3, RC A 2 : τ 2   m 2  τ 4, TT

39 Problem formulation  Given  The topology of the network G  The set of TT and RC frames F TT and F RC  The set of virtual links VL  The assignment of frames to virtual links M  For each frame the size, the deadline and the period

40 Problem formulation  Given  The topology of the network G  The set of TT and RC frames F TT and F RC  The set of virtual links VL  The assignment of frames to virtual links M  For each frame the size, the deadline and the period  Determine  The set of TT schedules

41 Problem formulation  Given  The topology of the network G  The set of TT and RC frames F TT and F RC  The set of virtual links VL  The assignment of frames to virtual links M  For each frame the size, the deadline and the period  Determine  The set of TT schedules  Such that  The deadlines for the TT and RC frames are satisfied  The end-to-end delay of RC frames is minimized

42 Motivational Example ES 1 ES 2 NS 1 ES 3 vl 3 vl 1 vl 2 period (us)deadline (us)C i (us) M f1 ∈ F RC 300 75 vl 1 f2 ∈ F TT 200 50 vl 2 f3 ∈ F TT 300 50 vl 3

43 Motivational Example ES 1 ES 2 NS 1 ES 3 vl 3 vl 1 vl 2 period (us) deadline (us) C i (us) M f1 ∈ F RC 300 75 vl 1 f2 ∈ F TT 200 50 vl 2 f3 ∈ F TT 300 50 vl 3  Initial TT schedule

44 Motivational Example ES 1 ES 2 NS 1 ES 3 vl 3 vl 1 vl 2 period (us) deadline (us) C i (us) M f1 ∈ F RC 300 75 vl 1 f2 ∈ F TT 200 50 vl 2 f3 ∈ F TT 300 50 vl 3  Optimized TT schedule

45 Optimization Strategy  TTEthernet Schedule Optimization (TTESO) strategy:  Tabu Search meta-heuristic  The TT schedules S  Such that:  TT and RC frames are schedulable  The end-to-end delay of the RC frames is minimized  Tabu Search  Minimizes the cost function  Explores the solution space using design transformations

46 Optimization Strategy  Degree of schedulability  Captures the difference between the worst-case delay and deadline  Cost Function

47 Optimization Strategy: Design Transformations  TT frame moves  advance frame transmission time  advance frame predecessors transmission time  postpone frame transmission time  postpone frame successors transmission time  RC frame moves  reserve space for RC frame  resize reserved space for RC frame  remove reserved space for RC frame

48 Frame Representation for Moves ES 1 ES 2 NS 1 NS 2 ES 3 ES 4 vl 1 f 1,1 [ES 1, NS 1 ] f 1,1 [NS 1, NS 2 ] f 1,1 [NS 1, NS 2 ] f 1,1 [NS 1, NS 2 ]

49 Design transformations: Postpone move

50 Design transformations: Advance move

51 Design transformations: Reserve space for RC

52 Design transformations: Resize RC reserved space

53 RC Frame End-to-End Analysis  On a dataflow link, a RC frame can be delayed by:  scheduled TT frames  queued RC frames  technical latency  policy specific:  timely block  pre-emption

54 RC Frame End-to-End Analysis ES 1 NS 2 NS 1 ES 4 vl 3 vl 2 vl 1 NS 3 NS 2 → NS 1 f 3,j 0 100200300400500600 f 4,1 NS 3 → NS 1 NS 1 → ES 4 f 2,1 ES 1 → NS 1 f 1,i f 2,1 f 4,1 f 1,i f 3,j C [NS 1, ES 4 ] f1f1 Q TT [NS 1, ES 4 ] Q RC [NS 1, ES 4 ] Q TL NS 1 R f1f1 vl 4

55 RC Frame End-to-End Analysis  Approaches for analysis of ARINC 644p7 network traffic:  Network Calculus, (Boyer, 2008)  Finite State Machine, (Saha, 2007)  Timed Automata, (Adnan, 2010)  Trajectory Approach, (Bauer, 2009)  We use the method proposed in (Steiner, 2011)  it takes into account also the TT traffic  it is pessimistic:  does not ignore frames that already delayed a RC frame on a previous link  assumes uniformly distributed intervals of equal length reserved for RC traffic

56 Experimental Results  Benchmarks  17 synthetic  1 real life test cases based on the SAE Automotive benchmark  TTESO compared to:  Straightforward Solution (SS)  Builds TT schedules with the goal of minimizing the end-to-end delay of TT frames, without considering the RC frames

57 Experimental Results

62 Conclusions  TTEthernet is very well suited for mixed-criticality applications  Predictability is achieved using three classes of traffic: TT, RC and BE  Spatial separation is achieved trough virtual links  Temporal separation is enforced by schedule tables for TT traffic and bandwidth allocation for RC traffic  We have addressed the optimization of the TTEthernet protocol  The TT schedules are determined such that TT and RC frames are schedulable, and the end-to-end delay of the RC frames is minimized  Optimization tools are needed to support the designer in order to obtain schedulable solutions  We have proposed a Tabu Search-based optimization solution

Synthesis of Communication Schedules for TTEthernet-based Mixed-Criticality Systems Domițian Tămaș-Selicean 1, Paul Pop 1 and Wilfried Steiner 2 1 Technical.

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Synthesis of Communication Schedules for TTEthernet-based Mixed-Criticality Systems Domițian Tămaș-Selicean 1, Paul Pop 1 and Wilfried Steiner 2 1 Technical.

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