IEC 61499 is a standard for designing industrial control systems using function blocks. Since its publication in 2005, several run-time environments have been developed as plausible implementations. Most of them, however, are poorly suited for use in safety-critical systems, as they are unable to guarantee deterministic behaviour and predictable timing. The use of different run-time environments results in subtle behavioural differences and complicates the effort of static timing analysis. We offer an alternative solution by leveraging the model-based approach to automatically synthesize multirate synchronous programs for a multitasking environment. Our approach preserves the well-known deterministic property of synchronous programs, while facilitating static timing analysis of IEC 61499 specifications. We achieve this without the need to introduce any foreign artefact to the standard. The schedulability criterion for tasks derived using our technique is given for the rate-monotonic scheduling policy. The viability of our approach is demonstrated through a code generator, which synthesizes multirate synchronous code for multi-task execution on the muC/OS-II real-time operating system.

Cyber-physical systems (CPS) are integrations of computation and control with sensing and actuation of the physical environment. Typically, such systems consist of embedded computers that monitor and control physical processes in a feedback loop. While modern electronic systems are increasingly characterized as CPS, their design and synthesis still rely on traditional methods, which lack systematic and automated techniques for accomplishment. Recently, IEC 61499 has been proposed as a standard for designing industrial process-control and measurement systems. It prescribes a component-based approach for developing industrial automation software using function blocks. Executable code can then be automatically generated and simulated from these function blocks. This bodes well for designers of CPS, who are more likely to be experts in specific industrial domains, rather than in computer science. The intuitive graphical nature and automatic code synthesis of IEC 61499 programs will alleviate the programming burden of industrial engineers, while ensuring more reliable software. While software synthesis from IEC 61499 programs is not new, the generation of efficient code from them has been wanting. This has made it difficult for function blocks to be used in software development for resource-constrained embedded controllers commonly employed in CPS. To address this, we present an approach that can generate very efficient code from function block descriptions. Experimental results from a benchmark suite shows that our approach produces substantially faster and smaller code compared to existing techniques.

The IEC 61499 standard defines a generic architecture for designing distributed industrial control systems based on function blocks. The standard, however, lacks a formal model of computation to describe the behavior of function block compositions. While various models have been prescribed in the literature to define the composite behavior on a single computational node, few have been proposed to directly address compositions in a distributed setting. This paper proposes a globally asynchronous locally synchronous (GALS) model for distributed function block systems. The model provides an abstract way to view communication between function blocks without implying yet any particular implementation. This abstraction can then be subsequently refined to obtain various implementations with different tradeoffs. We do so using an approach that is fully compatible with the standard's notion of communication function blocks, which abstract underlying communication mechanisms from the application. As a contribution, we have developed a compiler that automatically synthesizes separate programs for a given distributed function block system without needing any additional middleware or run-time environment to execute the resulting distributed code. The efficacy of the proposed approach is demonstrated through an industrial case study.

Esterel is a synchronous language suited for describing reactive embedded systems. It combines fine-grained parallelism with precise timing control for the execution of threads. Due to this, Esterel programs have typically been compiled into sequential code in software implementations, as tight synchronization between a large number of threads cannot be efficiently managed with an operating system (OS). This has enabled concurrent Esterel programs to be executed directly on single-core processors. Recently, however, multi-core processors have been increasingly used to achieve better performance in embedded applications. The conventional approach of generating sequential code from Esterel programs is unable to take advantage of multi-core processors. We overcome this limitation by compiling Esterel into a limited number of thread partitions (up to the number of available cores) to avoid the large overheads of implementing each Esterel thread separately within a conventional multithreading scheme. These partitions are then distributed onto separate cores using a static load balancing heuristic. The Esterel threads within a partition may then be dynamically scheduled with or without an OS. To evaluate the viability of this approach, we present experimental results comparing the execution of a set of benchmarks using one to four cores on the Intel Core 2 Quad with Linux, and one to two cores on the Xilinx Micro blaze without any OS. We have performed extensive benchmarking over large Esterel programs to illustrate that achieving throughput with parallel execution of Esterel is benchmark dependent.

IEC 61499 has been endorsed as the standard for modeling and implementing distributed industrial process measurement and control systems. The standard prescribes the use of function blocks for designing systems in a component-oriented approach. The execution model of a basic function block and the manner for event/data connections between blocks are described therein. Unfortunately, the standard does not provide exhaustive specifications for function block execution. Consequently, multiple standard-compliant implementations exhibiting different behaviors are possible. This not only defeats the purpose of having a standard but also makes verification of function block systems difficult. To overcome this, we propose synchronous semantics for function blocks and show its feasibility by translating function blocks into a subset of Esterel, a well-known synchronous language. The proposed semantics avoids causal cycles common in Esterel and is proved to be reactive and deterministic under any composition. Moreover, verification techniques developed for synchronous systems can now be applied to function blocks.