SCCharts: The Railway Project Report

SCCharts is a visual language proposed in 2012 for specifying safety-critical reactive systems. We present the results of the first medium sized SCCharts case-study. The case-study was conducted in the context of the railway project performed by students at the Kiel University in the summer term 2014. The railway project is a regularly occurring student training project that teaches principles of concurrent cyber-physical systems on a complex live model railway demonstrator. This report presents details of the first medium size SCCharts models created during the project. We explain what additional language extensions to SCCharts were necessary and how they were implemented. To handle performance issues that arose while developing the controller, compiler enhancements became necessary and are evaluated here. Furthermore, the participants completed a survey at the end of the project to confirm the goals that the SCCharts language and our SCCharts tool chain are suitable to build complex controllers. In the survey, the participants compared both, the SCCharts language and our SCCharts tools, with other modeling and classical programming languages and tools

Guidance in Model-based Compilations

The modeler should not be burdened with maintaining an overview over all potential conflicts. They should further be able to understand what is happening. Model-based compilers and modeling tools in general should guide a modeler.The KIELER Compiler constructs transformation snapshots and augmented models automatically during compilation. We demonstrate six different transient views that can help the modeler to refine their models and to solve modeling issues, such as causality problems in synchronous languages

Language Design for Reactive Systems: On Modal Models, Time, and Object Orientation in Lingua Franca and SCCharts

Reactive systems play a crucial role in the embedded domain. They continuously interact with their environment, handle concurrent operations, and are commonly expected to provide deterministic behavior to enable application in safety-critical systems. In this context, language design is a key aspect, since carefully tailored language constructs can aid in addressing the challenges faced in this domain, as illustrated by the various concurrency models that prevent the known pitfalls of regular threads. Today, many languages exist in this domain and often provide unique characteristics that make them specifically fit for certain use cases. This thesis evolves around two distinctive languages: the actor-oriented polyglot coordination language Lingua Franca and the synchronous statecharts dialect SCCharts. While they take different approaches in providing reactive modeling capabilities, they share clear similarities in their semantics and complement each other in design principles. This thesis analyzes and compares key design aspects in the context of these two languages. For three particularly relevant concepts, it provides and evaluates lean and seamless language extensions that are carefully aligned with the fundamental principles of the underlying language. Specifically, Lingua Franca is extended toward coordinating modal behavior, while SCCharts receives a timed automaton notation with an efficient execution model using dynamic ticks and an extension toward the object-oriented modeling paradigm

Interactive Model-Based Compilation: A Modeller-Driven Development Approach

There is a growing tendency for using domain-specific languages, which help domain experts to stay focussed on abstract problem solutions. It is important to carefully design these languages and tools, which fundamentally perform model-to-model transformations. The quality of both usually decides the effectiveness of the subsequent development and therefore the quality of the final applications. However, as the complexity and safety requirements of modern systems grow, it becomes increasingly burdensome to create highly customized languages and difficult to provide reasonable overviews within these tools. This thesis introduces a new interactive model-based compilation methodology. Compilations for arbitrary model-to-model transformations are themselves described as models. They can be instantiated for particular inputs, e. g. a program, to create concrete compilation runs, which return the result of that compilation. The compilation instance is interactively observable. Intermediate results serve as new inputs and as documentation. They can be used to create highly customized views and facilitate understandability. This methodology guides modellers from the start of the compilation to the final result so that they can interactively refine their models. The methodology has been implemented and validated as the KIELER Compiler (KiCo) and is available as part of the KIELER open-source project. It is used to implement the current reference compiler for the SCCharts language, a statecharts dialect designed for specifying safety-critical reactive systems based on a synchronous model of computation. The interactive model-based compilation approach was key to the rapid prototyping of three different compilation strategies, as well as new language extensions, variations and closely related languages. The results are verified with benchmarks, which are again modelled using the same approach and technology. The usability of the SCCharts language and the KiCo tooling is documented with long-term surveys and real-life industrial, academic and teaching examples

Time in SCCharts

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

SCCharts: The Mindstorms Report

SCCharts are a visual language proposed in 2012 for specifying safety-critical reactive systems. This is the second SCCharts report towards the usability of the SCCharts visual language and its KIELER SCCharts implementation. KIELER is an open-source project which researches the pragmatics of model-based languages and related fields. Nine case-studies that were conducted between 2015 and 2019 evaluate the pros and cons in the context of small-scale Lego Mindstorms models and similar projects. Par-ticipants of the studies included undergraduate and graduate students from our local and also external facilities, as well as academics from the synchronous community. In the surveys, both the SCCharts language and the SCCharts tools are compared to other modeling and classical programming languages and tools

Using SCCharts models in Simulink to model an electronic control unit

When constructing an electrical racing car, special attention needs to be directed to the development of its engine control unit. Functionality of the motor-torque calculation and the integration of advanced driver assistance systems are crucial for the speed handling and hence, the safety of the car. The Kieler Formula Student Team Raceyard, which since 2011 has been constructing electrical racing cars annually, so far designed and tested its controller model in the popular commercial modeling software MATLAB/Simulink. This work shows how a functionally equivalent system can be designed by utilizing the visual synchronous language SCCharts in the academic open-source project KIELER. A complete controller model is modeled in KIELER and validated to behave the same as the original controller both in Simulink directly as well as in the 3D simulation environment IPG Carmaker. Tests on the performance of both controllers show that while a slowdown can be observed when comparing the generated C Code, simulation time in IPG Carmaker only increases by a negligible factor. KIELER’s developing and testing capabilities for synchronous models can therefore be considered a valuable tool in the process of designing, tuning and documenting such a controller model

Time for Reactive System Modeling

Reactive systems interact with their environment by reading inputs and computing and feeding back outputs in reactive cycles that are also called ticks. Often they are safety critical systems and are increasingly modeled with highlevel modeling tools. The concepts of the corresponding modeling languages are typically aimed to facilitate formal reasoning about program constructiveness to guarantee deterministic output and are explicitly abstracted from execution time aspects. Nevertheless, the worst-case execution time of a tick can be a crucial value, where exceedance can lead to lost inputs or tardy reaction to critical events. This thesis proposes a general approach to interactive timing analysis, which enables the feedback of detailed timing values directly in the model representation to support timing aware modeling. The concept is based on a generic timing interface that enables the exchangeability of the modeling as well as the timing analysis tool for the flexible implementation of varying tool chains. The proposed timing analysis approach includes visual highlighting and modeling pragmatics features to guide the user to timing hotspots for timing related model revisions

Model Extraction of Legacy C Code in SCCharts

With increasing volumes of developed software and steadily growing complexity of these systems, software engineers struggle to manually maintain the vast amount of legacy code. Therefore, it is of interest to create a system which supports the documentation, maintenance, and reusability of software and its legacy code. The approach presented here automatically derives SCCharts models out of C code. These models can be used as visual documentation. By applying focus and context methods important parts of the model can be highlighted and may grant a better understanding of the overall software. Additionally, the models can also be used as a source to create new state-of-the-art code for various languages and platforms, such as C code or VHDL, using automatic code generators

Preserving Order during Crossing Minimization in Sugiyama Layouts

The Sugiyama algorithm, also known as the layered algorithm or hierarchical algorithm, is an established algorithm to produce crossing-minimal drawings of graphs. It does not, however, consider an initial order of the vertices and edges. We show how ordering real vertices, dummy vertices, and edge ports before crossing minimization may preserve the initial order given by the graph without compromising, on average, the quality of the drawing regarding edge crossings. Even for solutions in which the initial graph order produces more crossings than necessary or the vertex and edge order is conflicting, the proposed approach can produce better crossing-minimal drawings than the traditional approach