Martin Timmerman

Can Android be used for real-time purposes?

Android is thought as being yet another operating system! In reality, it is a software platform rather than just an OS; in practical terms, it is an application framework on top of Linux, which facilitates its rapid deployment in many domains. Android was originally designed to be used in mobile computing applications, from handsets to tablets to e-books. But developers are also looking to employ Android in a variety of other embedded systems that have traditionally relied on the benefits of true real-time operating systems performance, boot-up time, real-time response, reliability, and no hidden maintenance costs. In this paper, we present a preliminary conclusion about Androids real-time behavior and performance based on experimental measurements such as thread switch latency, interrupt latency, sustained interrupt frequency, and finally the behavior of mutex and semaphore. All these measurements were done on the same ARM platform (Beagleboard-XM). Our testing results showed that Android in its current state cannot be qualified to be used in real-time environments.

Open source FreeRTOS as a case study in real-time operating system evolution

Propose qualitative and quantitate benchmark suit for RTOS test.Perform performance tests and behavior tests to character FreeRTOS evolution process.Draw conclusions related to FreeRTOSs evolution which can be useful for the FreeRTOS group, other RTOS developments, and RTOS users. This paper studies the evolution of a real-time operating system, the open source FreeRTOS. We focus on the changes in real-time performance and behaviour over the last ten years. Six major release versions are benchmarked, presenting quantitative and qualitative development trends. We also use the available source code to discover the reasons for the changes. By analysing the results, we draw some conclusions related to this RTOSs evolution which can be useful for the FreeRTOS group, other RTOS developments, and also RTOS users.

An FPGA-based real-time event sampler

This paper presents the design and FPGA-implementation of a sampler that is suited for sampling real-time events in embedded systems. Such sampling is useful, for example, to test whether real-time events are handled in time on such systems. By designing and implementing the sampler as a logic analyzer on an FPGA, several design parameters can be explored and easily modified to match the behavior of different kinds of embedded systems. Moreover, the trade-off between price and performance becomes easy, as it mainly exists of choosing the appropriate type and speed grade of an FPGA family.

A Design That Incorporates Adaptive Reservation into Mixed-Criticality Systems

This paper presents a design and implementation of a Mixed-Criticality System (MCS) extended from źC/OS III. It is based on a MCS model that uses an adaptive reservation mechanism to cope with the uncertainties in task execution times and to increase the resource utilization in MCS. The implementation takes advantage of the tasksź recent execution records to predict their required computational resource in the near future and adjusts their reserved budget according to their criticality levels. The designed system focuses on soft real-time tasks. An overrun tolerance algorithm is used to limit the deadline miss ratios between a rise to the taskźs actual consumption and the change to the amount of reservation. More than two criticality levels can be handled without introducing obvious additional overhead at each added level. The case study evaluation demonstrates that the reserved resource for each task is always close to its actual consumption; the tasksź deadline misses are bounded by the different requirements specified by the criticality levels; during overload conditions, high-criticality tasks are guaranteed to have sufficient resource reservation. Although there is still room for improvement if it comes to processing overhead, this research brings some inspirations in both modelling and implementation aspects of MCS.

Behaviour and performance comparison between FreeRTOS and µC/OS-III

As the prevalence of embedded systems in various fields has spread, real-time operating systems (RTOSs) have been widely used for many years satisfying real-time requirements and a multitasking design. The use of RTOS adds additional overhead to a system, which should be deliberately considered and evaluated in some critical systems. This paper presents a qualitative and quantitative comparison between an open-source RTOS (FreeRTOS V8.0.0) and a commercial one (?C/OS-III). Both RTOS use a preemptive multitasking kernel, with additional support for round robin scheduling. We aim to benchmark and evaluate their performance and behaviour, including seven performance tests and two behaviour tests. Comparing the measurement results shows that the commercial µC/OS-III does not behave much better than FreeRTOS. Furthermore, we discovered that the priority changing function of µC/OSIII does not behave correctly in some circumstances. Although FreeRTOS has no such problem in the latest version, it still has a problem with its dynamic memory management.

Decentralized Multi-Robot Formation Control with Communication Delay and Asynchronous Clock

This paper investigates the leader–follower formation control problem for a group of networked nonholonomic mobile robots that are subject to bounded time-varying communication delays and an asynchronous clock. First we convert the formation control problem into a trajectory tracking problem, and then a fully distributed unified control framework based on the receding horizon control is implemented to converge the tracking errors. By adding an auxiliary acceleration term into the receding horizon controller, the framework is able to solve the impractical velocity jump problem. Considering the time-varying delays, the timing and order features of the messages are utilized to guarantee their logical correctness. To compensate for the delay effect, an improved control framework that exploits the predictability of the receding horizon controller is proposed. The asynchronous clock problem, which makes the communication delay unmeasurable, is studied. We give a definition of the syn point that is inspired from investigation of the property that messages are received out of order in a bounded time-varying delayed network. A novel method that detects the occurrence of syn points is integrated into the control framework to solve the asynchronous clock problem. Finally the effectiveness of the proposed approaches is demonstrated in the Player/Stage simulation environment.

EmSBoT: A lightweight modular software framework for networked robotic systems

Developing applications for modern complex networked robotic systems is more challenging due to the introduction of possibly sophisticated communication and coordination aspects. In this paper, we propose EmSBoT, a lightweight embedded component-based software framework targeting resource-constrained networked robotic systems. EmSBoT provides a unified Application Program Interface (API) that hides the heterogeneous distributed environment from applications. Its OS abstraction layer endows it with OS independence and portability. A port-based communication mechanism is adopted to exchange message between loosely coupled components, making the system with fault-tolerance capability. By isolating the communication channels as separate agents, the framework provides uniform and transparent message-passing for agents over node boundaries. We describe the architecture, programming model and core features of EmSBoT in this paper, together with the performance evaluation and behavior validation to demonstrate its efficiency and feasibility.

EmSBot: A modular framework supporting the development of swarm robotics applications

Component-based approaches are prevalent in software development for robotic applications due to their reusability and productivity. In this article, we present an Embedded modular Software framework for a networked roBoTic system (EmSBoT) targeting resource-constrained devices such as microcontroller-based robots. EmSBoT is primarily built upon μCOS-III with real-time support. However, its operating system abstraction layer makes it available for various operating systems. It employs a unified port-based communication mechanism to achieve message passing while hiding the heterogeneous distributed environment from applications, which also endows the framework with fault-tolerant capabilities. We describe the design and core features of the EmSBoT framework in this article. The implementation and experimental evaluation show its availability with small footprint size, effectiveness, and OS independence.