Markus Voelter

mbeddr: an extensible C-based programming language and IDE for embedded systems

While the C programming language provides good support for writing efficient, low-level code, it is not adequate for defining higher-level abstractions relevant to embedded software. In this paper we present the mbeddr technology stack that supports extension of C with constructs adequate for embedded systems. In mbeddr, efficient low-level programs can be written using the well-known concepts from C. Higher-level domain-specific abstractions can be seamlessly integrated into C by means of modular language extension regarding syntax, type system, semantics and IDE. In the paper we show how language extension can address the challenges of embedded software development and report on our experience in building these extensions. We show that language workbenches deliver on the promise of significantly reducing the effort of language engineering and the construction of corresponding IDEs. mbeddr is built on top of the JetBrains MPS language workbench. Both MPS and mbeddr are open source software.

mbeddr: instantiating a language workbench in the embedded software domain

Tools can boost software developer productivity, but building custom tools is prohibitively expensive, especially for small organizations. For example, embedded programmers often have to use low-level C with limited IDE support, and integrated into an off-the-shelf tool chain in an ad-hoc way.To address these challenges, we have built mbeddr, an extensible language and IDE for embedded software development based on C. mbeddr is a large-scale instantiation of the Jetbrains MPS language workbench. Exploiting its capabilities for language modularization and composition, projectional editing and multi-stage transformation, mbeddr is an open and modular framework that lets third parties add extensions to C with minimal effort and without invasive changes. End users can combine extensions in programs as needed.To illustrate the approach, in this paper we discuss mbeddr’s support for state machines, components, decision tables, requirements tracing, product line variability and program verification and outline their implementation. We also present our experience with building mbeddr, which shows that relying on language workbenches dramatically reduces the effort of building customized, modular and extensible languages and IDEs to the point where this is affordable by small organizations. Finally, we report on the experience of using mbeddr in a commercial project, which illustrates the benefits to end users.

Towards User-Friendly Projectional Editors

Today’s challenges for language development include language extension and composition, as well as the use of diverse notations. A promising approach is projectional editing, a technique to directly manipulate the abstract syntax tree of a program, without relying on parsers. Its potential lies in the ability to combine diverse notational styles – such as text, symbols, tables, and graphics – and the support for a wide range of composition techniques. However, projectional editing is often perceived as problematic for developers. Expressed drawbacks include the unfamiliar editing experience and challenges in the integration with existing infrastructure. In this paper we investigate the usability of projectional editors. We systematically identify usability issues resulting from the architecture. We use JetBrains Meta Programming System (MPS) as a case study. The case study discusses the concepts that MPS incorporates to address the identified issues, evaluates effectiveness of these concepts by surveying professional developers, and reports industrial experiences from realizing large-scale systems. Our results show that the benefits of flexible language composition and diverse notations come at the cost of serious usability issues – which, however, can be effectively mitigated with facilities that emulate editing experience of parser-based editors.

Design and Implementation of an Asynchronous Invocation Framework for Web Services

Asynchronous invocations are an important functionality in the context of distributed object frameworks, because in many situations clients should not block during remote invocations. There should be a loose coupling between clients and remote services. Popular web service frameworks, such as Apache Axis, offer only synchronous invocations (over HTTP). An alternative are messaging protocols but these implement a different communication paradigm. When client asynchrony is not supported, client developers have to build asynchronous invocations on top of the synchronous invocation facility. But this is tedious, error-prone, and might result in different remote invocation styles used within the same application. In this paper we build a framework using patterns for asynchronous invocation of web services. The framework design is based on the asynchrony patterns and other patterns from the same pattern language.

Pattern-Based Design of an Asynchronous Invocation Framework for Web Services

Asynchronous invocations are needed in the context of distributed object frameworks to prevent clients from blocking during remote invocations. Popular Web service frameworks offer only synchronous invocations (over HTTP). An alternative is messaging protocols but these implement a different communication paradigm. When client asynchrony is not supported, client developers have to build asynchronous invocations on top of the synchronous invocation facility. But this is tedious, error-prone, and might result in different remote invocation styles used within the same application. We present a number of patterns for asynchronous invocations and explain how these patterns can be used to build asynchronous invocation facilities for Web service frameworks. We exemplify this approach by explaining the design and implementation of an asynchronous invocation framework for Apache Axis.

Implementing modular domain specific languages and analyses

Domain specific languages allow users to directly express domain concepts in their programs and thereby eliminate the accidental complexity resulting from implementation details irrelevant to the domain. Cleaner programs, written in DSLs are much easier to analyze formally. However, domain specific analyses need to be implemented over and over again for each new domain specific language. In this paper we show that the use of language engineering techniques for modularizing languages can drastically improve on this situation. Language fragments (aka. language modules) together with a set of analyses defined for them can be reused between different DSLs, making the implementation of analyses significantly easier. This paper presents our approach for using the Meta-Programming System to implement domain specific languages and analyses both as extensions of C and in the domain of intelligent buildings. The main lesson learned is that modularization at language and analysis level allows rapid instantiation of advanced DSLs and their corresponding analyses.

Using C language extensions for developing embedded software: a case study

We report on an industrial case study on developing the embedded software for a smart meter using the C programming language and domain-specific extensions of C such as components, physical units, state machines, registers and interrupts. We find that the extensions help significantly with managing the complexity of the software. They improve testability mainly by supporting hardware-independent testing, as illustrated by low integration efforts. The extensions also do not incur significant overhead regarding memory consumption and performance. Our case study relies on mbeddr, an extensible version of C. mbeddr, in turn, builds on the MPS language workbench which supports modular extension of languages and IDEs.

Model driven software development in the context of embedded component infrastructures

In this chapter we motivate the need for an infrastructure platform for embedded software, supporting the development of reusable systems. Our solution is based on a component infrastructure that is implemented using model-driven software development (MDSD) techniques. This approach allows us to achieve the goal of re-usability while still providing an efficient system, tailored for the specific embedded hardware and operating system. This chapter explains the principles of our approach and introduces model-driven software development. It illustrates the concepts by presenting an example of how to model and specify the embedded application (a simple weather station), and how to generate supporting component middleware infrastructure from these models.

Extensible Debugger Framework for Extensible Languages

Language extension enables integration of new language constructs without invasive changes to a base language (e. g., C). Such extensions help to build more reliable software by using proper domain-specific abstractions. Language workbenches significantly reduce the effort for building such extensible languages by synthesizing a fully-fledged IDE from language definitions. However, in contemporary tools, this synthesis does not include interactive debugging for programs written with the base language or its extensions. This paper describes a generic framework for extensible debuggers that enables debugging of the language extensions by defining mappings between the base language and the language extensions. The architecture is designed for extensibility, so debug support for future extensions can be contributed with little effort. We show an implementation of our approach for mbeddr, which is an extensible version of the C programming language. We also discuss the debugger implementation for non-trivial C extensions such as components. Finally, the paper discusses the extent to which the approach can be used with other base languages, debugger backends and language workbenches.

Lessons learned from developing mbeddr: a case study in language engineering with MPS

Language workbenches are touted as a promising technology to engineer languages for use in a wide range of domains, from programming to science to business. However, not many real-world case studies exist that evaluate the suitability of language workbench technology for this task. This paper contains such a case study. In particular, we evaluate the development of mbeddr, a collection of integrated languages and language extensions built with the Jetbrains MPS language workbench. mbeddr consists of 81 languages, with their IDE support, 34 of them C extensions. The mbeddr languages use a wide variety of notations—textual, tabular, symbolic and graphical—and the C extensions are modular; new extensions can be added without changing the existing implementation of C. mbeddr’s development has spanned 10 person-years so far, and the tool is used in practice and continues to be developed. This makes mbeddr a meaningful case study of non-trivial size and complexity. The evaluation is centered around five research questions: language modularity, notational freedom and projectional editing, mechanisms for managing complexity, performance and scalability issues and the consequences for the development process. We draw generally positive conclusions; language engineering with MPS is ready for real-world use. However, we also identify a number of areas for improvement in the state of the art in language engineering in general, and in MPS in particular.