We introduce a systematic approach for automatically creating a visual diagram, akin to the graphical Safety Critical Application Development Environment (SCADE) model, from a Lustre program. This not only saves tedious manual drawing effort but also enables modeling software to automatically provide the developer with different meaningful views for the same program. We also extend the Sequentially Constructive Charts (SCCharts) language with data-flow constructs that adhere to the Lustre semantics, which permits a translation from Lustre to graphical SCCharts. This allows using the SCCharts code generation, simulation, and visualization tooling also for Lustre programs, in addition to the already existing Lustre compilation techniques. Furthermore, we investigate how the sequentially constructive model of computation, used in SCCharts and other synchronous languages, can be used to conservatively extend Lustre. We have implemented and validated this work with the Eclipse-based open-source Kiel Integrated Environment for Layout Eclipse Rich Client (KIELER) framework.

We discuss a novel approach for constructing deterministic reactive systems that revolves around a temporal model that incorporates a multiplicity of timelines. This model is central to Lingua Franca ( LF ), a polyglot coordination language and compiler toolchain we are developing for the definition and composition of concurrent components called reactors, which are objects that react to and emit discrete events. Our temporal model differs from existing models like the logical execution time (LET) paradigm and synchronous languages in that it reflects that there are always at least two distinct timelines involved in a reactive system; a logical one and a physical one—and possibly multiple of each kind. This article explains how the relationship between events across timelines facilitates reasoning about consistency and availability across components in cyber-physical systems (CPSs).

Complex software systems often feature distinct modes of operation, each designed to handle a particular scenario that may require the system to respond in a certain way. Breaking down system behavior into mutually exclusive modes and discrete transitions between modes is a commonly used strategy to reduce implementation complexity and promote code readability. The work in this paper aims to bring the advantages of working with modal models to mainstream programming languages, by following the polyglot coordination approach of Lingua Franca (LF), in which verbatim target code (e. g., C, C++, Python, Typescript, or Rust) is encapsulated in composable reactive components called reactors. Reactors can form a dataflow network, are triggered by timed as well as sporadic events, execute concurrently, and can be distributed across nodes on a network. With modal models in LF, we introduce a lean extension to the concept of reactors that enables the coordination of reactive tasks based on modes of operation.

Abstract In 2010, Fuhrmann et al. argued for enhancing modeler productivity by providing tooling that, put simply, combines the best of textual and graphical worlds. They referred to this as pragmatics , and argued that a key enabler would be the ability to automatically synthesize customized graphical views from a (possibly textual) model. The model would be the “ground truth” used, for example, for downstream code synthesis and simulation; the graphical views would typically be abstractions from the model serving various purposes, including documentation. Twelve years later, we reflect on their proposal, and illustrate the current state with the recently developed polyglot coordination language Lingua Franca (LF). LF has been designed with pragmatics in mind since early on, and some characteristics of LF make it particularly suited for pragmatics-aware programming and modeling. However, the underlying pragmatic principles are broadly applicable, and by now a set of mature open source tools is available for putting them into practice.

Software visualization tools can improve the software development process by providing a graphical overview of source code and enhancing collaboration. We here propose a concept to automatically extract mode diagrams from Blech code, an imperative synchronous programming language for embedded, reactive and safety-critical systems. Our main findings are that the visualization is helpful to understand the stateful nature of the source code and that it can enhance the collaboration between developers. It is also found, however, that a good understanding of the precise diagram semantics meaning of the diagram elements is key. Lastly, the findings indicate that preference on different labeling options is highly subjective.

Object orientation is a powerful and widely used paradigm for abstraction and structuring in programming. Many languages are designed with this principle or support different degrees of object orientation. In synchronous languages, originally developed to design embedded reactive systems, there are only few object-oriented influences. However, especially in combination with a statechart notation, the modeling process can be improved by facilitating object orientation as we argue here. At the same time the graphical representation can be used to illustrate the object-oriented design of a system. Synchronous statechart dialects, such as the SCCharts language, provide deterministic concurrency for specifying safety-critical systems. Using SCCharts as an example, we illustrate how an object-oriented modeling approach that supports inheritance can be introduced. We further present how external, i.e., host language, objects can be included in the SCCharts language. Specifically, we discuss how the recently developed concepts of scheduling directives and scheduling policies can be used to ensure the determinism of objects while retaining encapsulation.

Synchronous programming languages, such as Esterel, Lustre, SCADE or SCCharts, have been developed for designing reactive systems. They abstract from computation times and assume that outputs are synchronous with their inputs. This leads to a deterministic semantics, without race conditions, which makes synchronous languages particularly suitable for safety-critical systems. However, even though synchronous languages have been designed with real-time applications in mind, the handling of physical time is traditionally left to the execution environment. This makes e. g. the expression of arbitrary timeouts difficult and may lead to excessive “busy waiting” computations. The recent proposal of dynamic ticks alleviates this by making physical time a first-class citizen within the synchronous programming model. In this paper, we explore and demonstrate the practical merits of dynamic ticks, including improved timing accuracy and reduced computational requirements, in the context of Timed SCCharts. As demonstration platform, we present a hardware/software platform that involves two stepper motors whose operation must be synchronized at microsecond accuracy to avoid physical damage.

We introduce a systematic approach for automatically creating a visual diagram, akin to a SCADE model, from a Lustre program. This not only saves tedious manual drawing effort but also allows the creation of different views for the same program. Furthermore, we present an extension of the SCCharts language with data-flow constructs that adhere to the Lustre semantics, which in turn permits a translation from Lustre to graphical SCCharts. This allows to use the SCCharts simulation and code synthesis machinery as an alternative to existing Lustre compilation techniques. Finally, we investigate how the sequentially constructive model of computation underlying SCCharts can be used to conservatively extend Lustre, thus providing a deterministic semantics to some Lustre programs that would be rejected under its original semantics. We have implemented and validated this work with the Eclipse-based open-source KIELER framework.

We discuss a novel approach for constructing deterministic reactive systems that evolves around a temporal model which incorporates a multiplicity of timelines. This model is central to LINGUA FRANCA (LF), a polyglot coordination language and compiler toolchain we are developing for the definition and composition of concurrent components called Reactors, which are objects that react to and emit discrete events. What sets LF apart from other languages that treat time as a first-class citizen is that it confronts the issue that in any reactive system there are at least two distinct timelines involved; a logical one and a physical one-and possibly multiple of each kind. LF provides a mechanism for relating events across timelines, and guarantees deterministic program behavior under quantifiable assumptions.

A key to the synchronous principle of reconciling concurrency with determinism is to establish at compile time that a program is causal, which means that there exists a schedule that obeys the rules put down by the language. In practice it can be rather cumbersome for the developer to cure causality problems. To facilitate causality handling, we propose, first, to enrich the scheduling regime of the language to also consider explicit scheduling directives that can be used by either the modeler or model-to-model transformations. Secondly, we propose to enhance programming environments with dedicated causality views to guide the developer in finding causality issues. Our proposals should be applicable for synchronous languages; we here illustrate them for the SCCharts language and its open source development platform KIELER.

Object orientation is a powerful and widely used paradigm for abstraction and structuring in programming. Many languages are designed with this principle or support different degrees of object orientation. In synchronous languages, originally developed to design embedded reactive systems, there are only few object-oriented influences. However, especially in combination with a statechart notation, the modeling process can be improved by facilitating object orientation as we argue here. At the same time the graphical representation can be used to illustrate the object-oriented design of a system. Synchronous statechart dialects, such as the SCCharts language, provide deterministic concurrency for specifying safety-critical systems. Using SCCharts as an example, we illustrate how an object-oriented modeling approach that supports inheritance, can be introduced. We further present how external, i. e. host language, objects can be included in the SCCharts language. Specifically, we discuss how the recently developed concepts of scheduling directives and scheduling policies can be used to ensure the determinism of objects while retaining encapsulation.

Synchronous languages, such as the recently proposed SCCharts language, have been designed for the rigorous specification of real-time systems. Their sound semantics, which builds on an abstraction from physical execution time, make these languages appealing, in particular for safety-critical systems. However, they traditionally lack built-in support for physical time. This makes it rather cumbersome to express things like time-outs or periodic executions within the language. We here propose several mechanisms to reconcile the synchronous paradigm with physical time. Specifically, we propose extensions to the SCCharts language to express clocks and execution periods within the model. We draw on several sources, in particular timed automata, the Clock Constraint Specification Language, and the recently proposed concept of dynamic ticks. We illustrate how these extensions can be mapped to the SCChart language core, with minimal requirements on the run-time system, and we argue that the same concepts could be applied to other synchronous languages such as Esterel, Lustre or SCADE.