A Real-Time Linux Execution Environment for Function-Block Based Control Applications

1. 3rd IEEE Int. Conference on Industrial Informatics (INDIN), 10-12 August 2005, Perth, Australia A Real-Time Linux Execution Environment for Function-Block Based Control Applications Authors: George S. Doukas Kleanthis C. Thramboulidis Software Engineering Group Electrical & Computer Engineering University of Patras, Greece

2. Outline • IEC 61499 Function Block model • Archimedes System platform • RTAI based Execution Environment • Proposed FB Implementation Model • Performance Metrics • Conclusions INDIN 2005

3. IEC 61499 Function Block model • IEC61499 offers: • Flexibility • Reusability • Robustness • IEC61499 does not • exploit modern software engineering practices such as: • Model Driven Architecture • Component based development • address runtime implementation issues • provide means to capture real-time requirements INDIN 2005

4. Our approach • Corfu ESS • Integrates UML with the IEC 61499 model. • Archimedes System Platform • Provides the infrastructure required for FB-based distributed control applications to • exploit current Software Engineering practices • meet their real-time requirements and • allow re-configuration during run-time. INDIN 2005

5. Archimedes System Platform • exploits • the MIM (Model Integrated Mechatronics) paradigm in the development of Manufacturing Systems. • is comprised of: • a methodology, • an IEC-compliant Engineering Support System (Archimedes ESS), • a set of execution environments, on which the FB based control applications can be executed, and • a set of implementation frameworks, for the constructions of the application’s implementation models. INDIN 2005

6. Archimedes ESS • is a Toolkit • that supports the construction of IEC 61499-compliant Function Block based design models for distributed control and automation and their subsequent transformation to executable systems. • allows Model Driven Development, • it is based on the Generic Modeling Environment (GME), a configurable toolkit for creating domain-specific modeling and program synthesis environments. • can be easily extended to • allow QoS characteristics to be captured in the design model, • support various execution environments • automate the deployment process INDIN 2005

7. Development process INDIN 2005

8. IEC61499-compliant Execution Environment • FBRT • The 1st execution environment from Rockwell Automation (based on Java) • Archimedes system platform • provides various implementations of the execution environment • Real-time Linux • Real-time Java • CORBA Component Model (CCM) INDIN 2005

9. 3-Layer Execution Environment Architecture INDIN 2005

10. AE Layer Details ECM and DCM are used to obtain a flexible re-configurable implementation scheme for event and data connections. Each FB Container provides the execution context for one or more FB Instances. Favors run-time re-configuration. provides the deployment and re-deployment services of the AE Layer enables dynamic loading and management of FB Types. INDIN 2005

11. A real-time Linux Execution Environment • RTLinux • was adopted in our first prototype implementation • GPL version of RTLinux does not support user space programming. • RTAI (modular Hard RTOS based on Linux). • Allows user-space programming through LXRT • User threads have 2 modes of operation: • Soft RT → LXRT API & Linux system calls allowed. • Hard RT → Only LXRT API calls are allowed. • A thread can change operation mode anytime while keeping the same address context. • Is based on a Microkernel Architecture • Small HRT kernel handles RT tasks while Linux kernel runs as its lowest priority task (it operates transparently through a virtual interrupt mechanism). • Uses Priority based scheduling INDIN 2005

12. RTAI Implementation of AE layer Is implemented as a Soft RT Thread Passive entity (no thread) • Hard RT Thread(s). • Supports event or time triggered execution. • Multiple event queues allow handling events of different importance. Different event queues are handled by different threads. • One Hard RT Thread per FBContainer. • Event or Time Triggered execution. • Soft RT Thread. • Dynamic FBType loading through standard linux dynamic library loading machanism. INDIN 2005

13. FB Implementation Meta-Model • Our FB implementation model is based on 2 key constructs FB Type and FB Instance. • Object Oriented implementation alternatives: • Class – Instance relationship. • Tow different classes, with FBInstance class instances being associated to specific FBType class instances. • The more flexible second alternative is adopted. A FB instance of type B is implemented as an instance of the FBInstance class and is associated with the instance of class FBType that represents the FB type B. INDIN 2005

14. Implementation meta-model details INDIN 2005

15. Capturing real-time requirements Constraints such as end-to-end deadlines from input event MPPs to output event MPPs should be captured during design. Mechanical Process Parameters (MPPs) are used during application design to refer to actual parameters (event or data) read from or written to the controlled system. INDIN 2005

16. Event Path • Each EP is characterized by: • a deadline • a relative priority, that denotes its importance among EPs with the same deadline Event Path (EP): Denotes an event propagation path from an event source MPP to an event sink MPP through finite number of FBs within a FB Network. INDIN 2005

17. Assigning Scheduling parameters EP parameters are utilized to produce runtime priorities for FBs (FBContainers) and Events. Deadline Monotonic Like Algorithm INDIN 2005

18. Internet Application Deployment Process Download FBTypes INDIN 2005

19. Internet Application Deployment Process • Create FBInstances and inject them to FBContainers. • Set priorities of FBContainers. INDIN 2005

20. Internet Application Deployment Process • Create event & data connections • Intra-device • Inter-device INDIN 2005

21. FBType DLL Generation The FBType DLL defines a new class that extends the basic FBType class. … class FBType_TEST_FB : public FBType { private: static void algINIT(void *fbi) { FBInstance *fb=(FBInstance*)fbi; … } … static bool cond_START_TO_INIT(void *fbi) { FBInstance *fb=(FBInstance*)fbi; return GET_IE_INIT; } … public: FBType_TEST_FB() { //The constructor properly initializes FBType //class attributes.(FB interface, Internal //Variables, FB ECC, etc.) … } }; extern "C" { FBType* FBType_factory(void) { return new FBType_TEST_FB(); } } • FB Type algorithms and ECC transition conditions are mapped to class methods. • Class constructor initializes FBType class attributes that describe the FB type interface, the internal variables and the ECC. INDIN 2005

22. Performance Metrics Definition Key metrics definition is based on FB ECC operation state machine: • Sample inputs = f(#input_data, #input_events) • Evaluate transitions = f(#transitions, condition_complexity) • Perform actions = f(#actions, algorithm_exec_time) • Write output data = f(#output_data) • Issue generated events = f(#gen_events, #connections) INDIN 2005

23. Performance Metrics Environment Environment: • P4, 3GHz, 512 MB SDRAM (cache enabled) • RTAI 3.1 • Linux kernel 2.4.26 (SMP disabled) Assumptions: • All data 4 bytes long • Negligible complexity of transition condition expressions • Actions: 1 dummy algorithm & 1 generated event • Only one event is delivered to FBs for each activation • Measurements made by high priority threads to avoid preemption INDIN 2005

24. Performance Metrics Results (1) INDIN 2005

25. Performance Metrics Results (2) INDIN 2005

26. Performance Metrics Results (3) INDIN 2005

27. Performance Metrics Results (4) INDIN 2005

28. Performance Metrics Results (5) Maximum local event connection latency = 15μS INDIN 2005

29. Performance Metrics Result Evaluation • Results of time measurements depict: • the efficiency of the proposed execution environment • local event connection latency 15μS of which just 2,6μS is the propagation delay within ECM • while one shot timer setup time as reported by RTAI is 2μS • the predictability of the execution environment • all measurement indicate that execution time is linearly affected by the variable parameters INDIN 2005

30. Teabag Boxing System case study • An example control application of TBS based has been developed to: • demonstrate the applicability of the proposed approach • test the efficiency of the proposed execution environment and FB implementation model • test re-configurability of the proposed execution environment • The example application can be downloaded on request from http://seg.ee.upatras.gr/MIM INDIN 2005

31. M1 S2 S4 S0 S3 S6 Conveyor-1 belt-1 Conveyor-1 belt-2 M4 M3 M2 S5 Scale Conveyor -2 S1 M5 Teabag Boxing System case study INDIN 2005

32. Conclusions • The proposed FB implementation model : • offers great degree of flexibility • supports dynamic runtime loading of FB types in any OO language. • The proposed execution environment: • allows run-time reconfiguration • offers real-time predictability (RTAI) • The adopted application development process: • supports Model Driven Architecture • allows real-time requirements capturing during application design • enables automatic transformation of design model to implementation model and semi-automatic application deployment INDIN 2005

33. A Real-Time Linux Execution Environment for Function-Block Based Control Applications MIM & Archimedes web site http://seg.ee.upatras.gr/MIM/ INDIN 2005