1. 2004-11-23 @ SaabTech Jönköping FLEXCON Flexible Embedded Control Systems

2. 2004-11-23 @ SaabTech Jönköping FLEXCON = Real-Time & Control Real-Time Computing Control Engineering FLEXCON Control in Real-Time Computing Real-Time Techniques in Control System Implementation

3. 2004-11-23 @ SaabTech Jönköping Temporal Non-Determinism Decreases: –improvements in worst-case analysis methods –tool development –development of more deterministic implementation techniques Increases: –developments in general purpose computer systems –new types of applications, e.g., Internet-based, operating in open and unpredictable environments –next generation micro-chips stochastics will play a larger role sacrifice temporal determinism to maintain functional determinism Increasing, at least for non-critical systems.....

4. 2004-11-23 @ SaabTech Jönköping Flexibilitet F m.a.p osäkerhet om resursutnyttjande F m.a.p osäkerhet om egenskaper hos implementationsplattform F m.a.p. osäkerhet om extern omgivning F m.a.p. osäkerhet om # tasks (last) F m.a.p. specifikationer (interval/max/min vs fixa värden) F m.a.p. dynamisk systemuppdatering (plug’n play) (komponenter, applikationer, systemprogramvara) F. i bemärkelsen event-triggered vs time-triggered (dynamic vs static) F. i utvecklingsprocessen (vid design-time), använda komponenter etc, konfigurering, F. m.a.p. virtuell resp fysisk miljö

5. 2004-11-23 @ SaabTech Jönköping WP1: Flexibility in real-time embedded control system design using COTS platforms, languages and components Component Technology (Ivica Crnkovic) –embedded control systems –real-time issues –flexibility –PhD student Johan Fredriksson (2003) (SAVE) Language Technology – Java (Klas Nilsson) –dynamic aspects –flexibility –PhD student Sven Gestegård Robertz Cont. of ARTES project Feedback scheduling in dynamic memory allocation (RT-Java)

6. 2004-11-23 @ SaabTech Jönköping WP23 WP2: Control-Based Approaches in Embedded Systems WP3: Quality-of-Service and Resource Negotiation in Embedded Control Combined into a single WP with focus on control systems

7. 2004-11-23 @ SaabTech Jönköping Temporal Determinism Computer-based control theory is based on –equidistant sampling –negligible input-output latencies that can be ignored or constant latencies that easily can be compensated for Reality: –Varying execution times due to preemption, blocking, data- dependencies, caches, pipelines, network communication, … Result: –Sampling interval jitter –Non-negligible and varying latencies

8. 2004-11-23 @ SaabTech Jönköping Control Community A new implementation and resource-aware control paradigm is needed! Resource-Constrained Control

9. 2004-11-23 @ SaabTech Jönköping Hard Control Implementation Approach Strive to maximize the temporal determinism E.g. using time-triggered and synchronous programming models Pros: –Simplifies attempts at formal verification for, e.g. safety-critical applications –However, a large amount of ”hard” real-time control applications are not safety-critical Cons: –Often requires special purpose solutions, i.e., less efficient and more expensive –Requires complete knowledge about resource utilization, load,.. –May result in under-utilized systems with possibly poor control performance

10. 2004-11-23 @ SaabTech Jönköping Hard R-T Task Model Periodic/sporadic tasks with constant period, hard deadline, and known WCET Just a model: –Does not fit all control problems E.g. hybrid controllers, event-based controllers –Overly restrictive for most control problems a missed deadline no catastrophy a late control signal is better than no signal at all

11. 2004-11-23 @ SaabTech Jönköping Soft Control Implementation Approach View the temporal nondeterminism caused by the implementation platform as an uncertainty or disturbance acting on the control loop Use control-based approach –Inherent robustness of feedback –Design for robustness against implementation uncertainties –Active compensation, cp feedforward from measurable disturbances and adaptive control

12. 2004-11-23 @ SaabTech Jönköping Implementation-Robust Control A tremendous amount of theory for plant uncertainties ? Very little theory for implementation platform uncertainties ?

13. 2004-11-23 @ SaabTech Jönköping Implementation-Robust Control 1.Temporal robustness timing variations Theory that allows us to decide which level of temporal determinims that a given control loop really requires in order to meet given objectives on stability and performance Is it necessary to use a time-triggered approach or will an event- triggered approach do? How large jitter in sampling interval and i-o latency can be tolerated? Is it Ok to now and then skip a sample? ….. 2.Functional robustness Fault-tolerance towards computer-level faults leading to data errors An increasing problem in future deep sub-micron technology hardware

14. 2004-11-23 @ SaabTech Jönköping Resource Allocation as a Control Problem In an applications with multiple (control) tasks the dynamic allocation of resources to the tasks can be viewed as a control problem in itself! The control performance can be viewed as a quality-of-service attribute (Quality-of- Control)

15. 2004-11-23 @ SaabTech Jönköping Control in Real-Time Computing Use of control-based approaches for uncertainty management in large real-time computer and communication systems is receiving increased attention The worst-case approach no longer feasible Feedback, feedforward,... Control-oriented models capturing dynamics

16. 2004-11-23 @ SaabTech Jönköping Feedback Scheduling Dynamic on-line allocation of computing resources Feedback from actual resource utilization In principle, any computing resource

17. 2004-11-23 @ SaabTech Jönköping Feedback Scheduling Structures Feedback –Reactive Feedforward –Proactive –Mode changes and admission control

18. 2004-11-23 @ SaabTech Jönköping Requirements on Scheduling Theory Relax the standard hard-real time assumptions Theory that better matches the needs of control systems

19. 2004-11-23 @ SaabTech Jönköping Requirements on Control Theory Co-design methods –control design methods that take resoure constraints into account Improved understanding of how temporal non-determinism effect control performance –analysis methods –Tools Theory for aperiodic systems

20. 2004-11-23 @ SaabTech Jönköping Examples of recent developments Jitterbug (Cervin, Lincoln): –Matlab toolbox –analysis of how sampling period and i/o delay distributions effect control performance TrueTime (Cervin, Henriksson): –Simulink toolbox –co-simulation of temporal effects of real-time kernels and communication networks, and control performance New simple stability results (Lincoln): –control loops with variations in delay –networked control loops

21. 2004-11-23 @ SaabTech Jönköping Jitterbug

22. 2004-11-23 @ SaabTech Jönköping TrueTime

23. 2004-11-23 @ SaabTech Jönköping Tool Usage Scheduling Parameters (T,D,Prio, …) Task Timing Parameters (latencies, jitter, …) Control Performance (variance, rise time, overshoot, ….) Complex, ”nonlinear” relationship Non-trivial relationship Simulation with TrueTime Analysis with Jitterbug

24. 2004-11-23 @ SaabTech Jönköping WP4: Testing-Based Verification and Monitoring of Embedded Control Systems Högskolan i Skövde (Sten Andler) Focus on event-driven control systems Run-time properties for testability Test case selection and generation. Connection to MdH (Thane)

25. 2004-11-23 @ SaabTech Jönköping WP5: Robotics and Automation Demonstrator Common platform for demonstrating project results Maintain the project focused Not a “moon-lander” demonstrator Based on Robotics Laboratory in Lund (Klas Nilsson) EU project HRTC, incl. TTP EU project AUTOFETT with ABB, … Strong links to ABB EU project SMErobot starting...

26. 2004-11-23 @ SaabTech Jönköping Thing in common with Saab Separation of concerns, modularity Multi-CPU VME+PCI/PMC systems Dependable communication/control COTS hardware Long-lasting platforms Safe execution Testing and monitoring Combination with formal methods desired Engineering efficiency/practices....

27. 2004-11-23 @ SaabTech Jönköping Possible SaabTech Issues Flexibility techniques for improved robustness Combining – for mission-critical systems: –Safe languages (Well-defined execution) –Certified run-time techniques (VM+HW) –Safe partitioning with shared resources. –Formal verification (FLEXCON+SAVE) –Improved testing techniques (pre-runtime) –Embedded on-line monitoring (run-time) Questions?