Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems

This report describes the work carried out within the research project ``Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems''. The overall objective of the work has been to develop integrated control and scheduling methods for improving the performance of real-time control systems with limited resources. The work has fallen into three categories. First, overrun methods for control tasks has been investigated. Specifically, a reservation-based scheduling concept called the Control Server has been further developed, and control experiments on a ball-and-place process have been performed. Second, the issue of jitter in real-time control systems has been explored. The concept of Jitter Margin has been introduced as a link between control stability theory and scheduling theory. In this context, best-case response-time analysis under earliest-deadline-first scheduling has been researched. Third, some development work on the S.Ha.R.K. real-time kernel has been performed. The rate-monotonic and earliest-deadline-first scheduling modules have been extended, and new modules for the elastic task model and the control server model have been implemented

A hierarchical scheduling model for component-based real-time systems

In this paper, we propose a methodology for developing component-based real-time systems based on the concept of hierarchical scheduling. Recently, much work has been devoted to the schedulability analysis of hierarchical scheduling systems, in which real-time tasks are grouped into components, and it is possible to specify a different scheduling policy for each component. Until now, only independent components have been considered. In this paper, we extend this model to tasks that interact through remote procedure calls. We introduce the concept of abstract computing platform on which each component is executed. Then, we transform the system specification into a set of real-time transactions and present a schedulability analysis algorithm. Our analysis is a generalization of the holistic analysis to the case of abstract computing platforms. We demonstrate the use of our methodology on a simple example

Timing Analysis of the FlexRay Communication Protocol

FlexRay will very likely become the de-facto standard for in-vehicle communications. However, before it can be successfully used for safety-critical applications that require predictability, timing analysis techniques are necessary for providing bounds for the message communication times. In this paper, we propose techniques for determining the timing properties of messages transmitted in both the static (ST) and the dynamic (DYN) segments of a FlexRay communication cycle. The analysis techniques for messages are integrated in the context of a holistic schedulability analysis that computes the worst-case response times of all the tasks and messages in the system. We have evaluated the proposed analysis techniques using extensive experiments. 1

Schedulability-Driven Frame Packing for Multi-Cluster Distributed Embedded Systems

We present an approach to frame packing for multi-cluster distributed embedded systems consisting of time-triggered and event-triggered clusters, interconnected via gateways. In our approach, the application messages are packed into frames such that the application is schedulable. Thus, we have also proposed a schedulability analysis for applications consisting of mixed event-triggered and time-triggered processes and messages, and a worst case queuing delay analysis for the gateways, responsible for routing inter-cluster traffic. Optimization heuristics for frame packing aiming at producing a schedulable system have been proposed. Extensive experiments and a real-life example show the efficiency of our frame-packing approach

An Integrated Framework for Multiprocessor, Multimoded Real-Time Applications

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-30598-6_2In this paper we propose an approach for building real-time systems under a combination of requirements: specification and handling of operating modes and mode changes; implementation on top of a multiprocessor platform; integration of both aspects within a common framework; and connection with schedulability analysis procedures. The proposed approach uses finite state machines to describe operating modes and transitions, and a framework of real-time utilities that implements the required behaviour in Ada 2012. Automatic code generation plays an important role: the system is derived from the functional and timing specification, and implemented according to the abstractions provided by the framework. Response time analysis enables assessing the schedulability of the different operating modes and the transitions between modes.This work was partially supported by the Vicerrectorado de Investigación of the UPV (PAID-06-10-2397), Ministerio de Ciencia e Innovación (TIN2011-28567-C03- 03) and European Union (FP7-ICT-287702)Sáez Barona, S.; Real Sáez, JV.; Crespo, A. (2012). An Integrated Framework for Multiprocessor, Multimoded Real-Time Applications. En Reliable Software Technologies – Ada-Europe 2012. Springer. 18-34. https://doi.org/10.1007/978-3-642-30598-6_21834Wellings, A.J., Burns, A.: A Framework for Real-Time Utilities for Ada 2005. Ada Letters XXVII(2) (August 2007)Real, J., Crespo, A.: Incorporating Operating Modes to an Ada Real-Time Framework. Ada Letters 30(1) (April 2010)Sáez, S., Terrasa, S., Crespo, A.: A Real-Time Framework for Multiprocessor Platforms Using Ada 2012. In: Romanovsky, A., Vardanega, T. (eds.) Ada-Europe 2011. LNCS, vol. 6652, pp. 46–60. Springer, Heidelberg (2011)Joseph, M., Pandya, P.: Finding response times in a real-time system. British Computer Society Computer Journal 29(5), 390–395 (1986)Audsley, N., Burns, A., Richardson, M., Tindell, K., Wellings, A.J.: Applying new scheduling theory to static priority pre-emptive scheduling. Software Engineering Journal 8(5), 284–292 (1993)Real, J., Crespo, A.: Mode Change Protocols for Real-Time Systems: A Survey and a new Proposal. Real-Time Systems 26(2), 161–197 (2004)Harel, D.: Statecharts: A visual formalism for complex systems. The Science of Computer Programming 8(3), 231–274 (1987)Object Management Group: Unified Modeling Language (OMG UML) V2.4 (August 2011), http://www.omg.org/spec/UML/2.4.1Sáez, S., Terrasa, S., Lorente, V., Crespo, A.: Implementing Reactive Systems with UML State Machines and Ada 2005. In: Kordon, F., Kermarrec, Y. (eds.) Ada-Europe 2009. LNCS, vol. 5570, pp. 149–163. Springer, Heidelberg (2009)Burns, A., Wellings, A.J.: Dispatching Domains for Multiprocessor Platforms and their Representation in Ada. In: Real, J., Vardanega, T. (eds.) Ada-Europe 2010. LNCS, vol. 6106, pp. 41–53. Springer, Heidelberg (2010)Barnett, J.: State Chart XML (SCXML): State Machine Notation for Control Abstraction (May 2008), http://www.w3.org/TR/scxml

Optimizing Logical Execution Time Model for Both Determinism and Low Latency

The Logical Execution Time (LET) programming model has recently received considerable attention, particularly because of its timing and dataflow determinism. In LET, task computation appears always to take the same amount of time (called the task's LET interval), and the task reads (resp. writes) at the beginning (resp. end) of the interval. Compared to other communication mechanisms, such as implicit communication and Dynamic Buffer Protocol (DBP), LET performs worse on many metrics, such as end-to-end latency (including reaction time and data age) and time disparity jitter. Compared with the default LET setting, the flexible LET (fLET) model shrinks the LET interval while still guaranteeing schedulability by introducing the virtual offset to defer the read operation and using the virtual deadline to move up the write operation. Therefore, fLET has the potential to significantly improve the end-to-end timing performance while keeping the benefits of deterministic behavior on timing and dataflow. To fully realize the potential of fLET, we consider the problem of optimizing the assignments of its virtual offsets and deadlines. We propose new abstractions to describe the task communication pattern and new optimization algorithms to explore the solution space efficiently. The algorithms leverage the linearizability of communication patterns and utilize symbolic operations to achieve efficient optimization while providing a theoretical guarantee. The framework supports optimizing multiple performance metrics and guarantees bounded suboptimality when optimizing end-to-end latency. Experimental results show that our optimization algorithms improve upon the default LET and its existing extensions and significantly outperform implicit communication and DBP in terms of various metrics, such as end-to-end latency, time disparity, and its jitter