Roberto Brega

Swiss Federal Institute of Technology (ETH), Institute of Robotics (IfR), Alumnus

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Reliability in real-time: Why strong-typed programming languages matter

A Real-Time Operating System Designed for Predictability and Run-Time Safety

Complex embedded machines are usually controlled by an application software sitting on top of a r... more Complex embedded machines are usually controlled by an application software sitting on top of a real-time oper- ating system. Thus, the safety issues involved do not apply only to the mechanical structure or to the elec- tronic circuitry, but also to the software that is responsi- ble for an efficient run-time and predictable error- handling. The single, least reliable, nonredundant

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The need for autonomy and real-time in mobile robotics: Case study of Pygmalion and XO/2

Starting from a user point of view the paper discusses the requirements of a development environm... more Starting from a user point of view the paper discusses the requirements of a development environment (operating system and programming language) for mechatronic systems, especially mobile robots. We argue that user requirements from research, education, ergonomics and applications impose a certain functionality on the embedded operating system and programming language, and that a deadline-driven real-time operating system helps to fulfil these requirements. A case study of the operating system XO/2, its programming language Oberon-2 and the mobile robot Pygmalion is presented. XO/2 explicitly addresses issues like scalabilty, safety and abstraction, previously found to be relevant for many user scenarios.

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The need for autonomy and real-time in mobile robotics: a case study of XO/2 and Pygmalion

Proceedings. 2000 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2000) (Cat. No.00CH37113), 2000

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Application of a nonlinear adaptive controller to a 6 DOF parallel manipulator

Proceedings 2000 ICRA. Millennium Conference. IEEE International Conference on Robotics and Automation. Symposia Proceedings (Cat. No.00CH37065), 2000

Nonlinear adaptive control schemes for robotic manipulators or new types of high speed machine to... more Nonlinear adaptive control schemes for robotic manipulators or new types of high speed machine tools with nonlinear dynamics are well suited to keep the tracking errors low, even at high speeds. Their application however requires fast microprocessors and an operating system that allows implementing the control algorithms as hard real-time tasks. The paper presents the implementation of a nonlinear model-based

May you have a strong (-typed) foundation" why strong-typed programming languages do matter

IEEE International Conference on Robotics and Automation, 2004. Proceedings. ICRA '04. 2004, 2004

Programming efficient and reliable code can be considered a non-trivial task, as it requires deep... more Programming efficient and reliable code can be considered a non-trivial task, as it requires deep understanding of the problem to be solved along with good programming skills. However, software frameworks and programming paradigms can provide a dependable infrastructure upon which better programs can be written and deployed. This allows engineers to focus mainly on their task, while relying on the underlying run-time environment for taking care of low-level programming issues, such as memory allocation and disposal, typing consistency and interface compliance. 1 In this paper, we argue that strong-typed programming languages and paradigms offer a valid support for the production of reliable programs. Aware of the challenges of formal measurement metrics for code quality, we present the benefits of strong-typing by considering a practical application: The design and implementation of RoboX, a tour-guide robot for the Swiss National Exhibition Expo.02. The example is extremely well suited for such a discussion, since complex mechatronic applications can be considered critical systems-i.e. systems whose failure may endanger missions, lives and society-thus their reliability has to be made a prime concern.

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A personal robot for mechatronic application programmers. The role of automatic storage reclamation and programming languages in the lifetime of a safe mechatronic system

A software system can be called a safe-system with respect to dynamic memory, when it supports on... more A software system can be called a safe-system with respect to dynamic memory, when it supports only strong-typing and it doesn't allow for the manual disposal of dynamic memory. The first aspect guarantees that untyped, potentially dangerous operations are caught by the compiler or by run-time checks. The second issue is solved by the utilisation of an automatic memory reclamation scheme, i.e., a garbage collector. We present the implementation of these strategies in the real-time operating system XO/2, and how they have contributed to the realisation of the Mobile Mail Distribution System MoPS, developed at the Institute of Robotics of the ETH Zurich, Switzerland

A complex mechatronic system: from design to application

Progress in mobile robotics requires the researchers to access and improve all modules that compo... more Progress in mobile robotics requires the researchers to access and improve all modules that compose the robot, from low-level mechanical components to highlevel reasoning systems. This paper presents the development process of the robots built at the Autonomous Systems Lab, EPFL Lausanne, Switzerland. Starting from the mechanical and electrical design up to the application, we show the challenges that needed to be faced as well as the solutions that have been devised. The description covers aspects like the operating system and framework, because of its role in the overall safety and dependability of the whole software system, the research as a precondition for innovative products, and the man-machine interface, which is indispensable for conveying information to the user as well as allowing the user to interact with the robot. The issues that have been faced stem from the hierarchical, layered construction of a complex mechatronic product, where the operation of the machine depends on the smooth cooperation of each layer; In the same way, the overall safety is undermined by the least reliable piece building the system. 1 2

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Approximation of Worst-Case Execution Time for Preemptive Multitasking Systems

by Matteo Corti and Roberto Brega

The control system of many complex mechatronic products requires for each task the Worst Case Exe... more The control system of many complex mechatronic products requires for each task the Worst Case Execution Time (WCET), which is needed for the scheduler's admission tests and subsequently limits a task's execution time during operation. If a task exceeds the WCET, this situation is detected and either a handler is invoked or control is transferred to a human operator. Such control systems usually support preemptive multitasking, and if an object-oriented programming language (e.g., Java, C++, Oberon) is used, then the system may also provide dynamic loading and unloading of software components (modules). Only modern, state-of-the art microprocessors can provide the necessary compute cycles, but this combination of features (preemption, dynamic un/loading of modules, advanced processors) creates unique challenges when estimating the WCET. Preemption makes it difficult to take the state of the caches and pipelines into account when determining the WCET, yet for modern processors, a WCET based on worst-case assumptions about caches and pipelines is too large to be useful, especially for big and complex real-time products. Since modules can be loaded and unloaded, each task must be analyzed in isolation, without explicit reference to other tasks that may execute concurrently. To obtain a realistic estimate of a task's execution time, we use static analysis of the source code combined with information about the task's runtime behavior. Runtime information is gathered by the performance monitor that is included in the processor's hardware implementation. Our predictor is able to compute a good estimation of the WCET even for complex tasks that contain a lot of dynamic cache usage, and its requirements are met by today's performance monitoring hardware. The paper includes data to evaluate the effectiveness of the proposed technique for a number of robotics control kernels that are written in an object-oriented programming language and execute on a PowerPC 604e-based system.

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