Scheduling periodic tasks in a hard real-time environment

We consider a real-time scheduling problem that occurs in the design of software-based aircraft control. The goal is to distribute tasks $au_i=(c_i,p_i)$ on a minimum number of identical machines and to compute offsets $a_i$ for the tasks such that no collision occurs. A task $au_i$ releases a job of running time $c_i$ at each time $a_i + kcdot p_i,k in mathbb{N}_0$ and a collision occurs if two jobs are simultaneously active on the same machine. We shed some light on the complexity and approximability landscape of this problem. Although the problem cannot be approximated within a factor of $n^{1-varepsilon}$ for any $varepsilon>0$, an interesting restriction is much more tractable: If the periods are dividing (for each $i,j$ one has $p_i | p_j$ or $p_j | p_i$), the problem allows for a better structured representation of solutions, which leads to a 2-approximation. This result is tight, even asymptotically

Component-Based Real-Time Operating System for Embedded Applications

Acceptance rate: 37%, Rank (CORE): AInternational audienceAs embedded systems must constantly integrate new functionalities, their developement cycles must be based on high-level abstractions, making the software design more flexible. CBSE provides an approach to these new requirements. However, low-level services provided by operating systems are an integral part of embedded applications, furthermore deployed on resource-limited devices. Therefore, the expected benefits of CBSE must not impact on the constraints imposed by the targetted domain, such as memory footprint, energy consumption, and execution time. In this paper, we present the componentization of a legacy industry-established Real-Time Operating System, and how component-based applications are built on top of it. We use the Think framework that allows to produce flexible systems while paying for flexibility only where desired. Performed experimentions show that the induced overhead is negligeable

Solving an Avionics Real-Time Scheduling Problem by Advanced IP-Methods

We report on the solution of a real-time scheduling problem that arises in the design of software-based operation control of aircraft. A set of tasks has to be distributed on a minimum number of machines and offsets of the tasks have to be computed. The tasks emit jobs periodically starting at their offset and then need to be executed on the machines without any delay. Also, further constraints in terms of memory usage and redundancy requirements have to be met. Approaches based on standard integer programming formulations fail to solve our real-world instances. By exploiting structural insights of the problem we obtain an IP-formulation and primal heuristics that together solve the real-world instances to optimality and outperform text-book approaches by several orders of magnitude. Our methods lead, for the first time, to an industry strength tool to optimally schedule aircraft sized problems

The challenges of embedded systems engineering (Abstract of keynote speech)

Embedded system technology has become an important, if not dominating component in the realization of all sorts of high-tech products, machines, and infrastructures. The temptation to create systems with new, powerful, intelligent features has turned embedded software into an essential high-tech ingredient that, exploiting the hardware capabilities afforded by Moore’s law, is subject to exponential growth. As has been pointed out by many authors before, the complexity of the embedded software is not just a product of its growing size, but also results from the required relation between the software and its physical environment, both in terms of its execution on physical platforms and in its interaction with the system environment. This combination of digital control and physical phenomena makes it plausible that hybrid modelling and hybrid systems theory have a role to play in the design of embedded systems. Last year Henzinger and Sifakis (The Embedded Systems Design Challenge) suggested that we need the development of more physically informed models of computation combining analytical and constructive elements. This would provide a more fundamental basis for embedded systems design, as well as provide a much needed paradigmatic change for computer science. Being in principle sympathetic to the proposed programme from a scientific point of view, in this talk we want to examine what are the most pressing problems from an engineering point of view, in particular from the overall system perspective. The software complexity of high-tech systems is often related to the system integration, and not to the embedded software of individual components. The interpretation of the required integral functionality usually includes engineering disciplines beyond those related to hardware, software, and control, with particular methods, models, and tools. It remains to be seen whether deep (i.e. at the semantic level) integration of relevant models and methods will ultimately outperform more loosely coupled coalitions of specialized approaches that are closer to the cultures of the contributing disciplines. Another practically dominant concern often is the sheer size of the collective system software. Alternative approaches to design, therefore, must scale up and support the management of large quantities of design software (programs, models, specifications, etc.). In our presentation we will draw on a number of big industry-as-laboratory projects carried out by the Embedded Systems Institute

On bicontinuous bisimulation and the preservation of stability

Since Pappas et all. transferred the notion of bisimulation from computer science to control theory, it has attracted quite some attention in the hybrid systems community[1]. Notably, bisimulation relations are used to reduce the complexity of dynamic systems, while preserving reachability notions [1]. In [2], we argued that bisimulation needs to be strengthened with continuity conditions, in order to preserve other control science notions as well. This idea was independently explored in [3,4,5] where modal and temporal logics are extended with topological operators, to be able to reason about robustness of a control strategy for embedded systems

Properties of BuST and timed-token protocols in managing hard real-time traffic

Token passing channel access mechanisms are used in several communication networks. An important class of token passing approaches are the so-called timed token protocols, which are able to manage both real-time traffic and non real-time traffic. Recently, a new token passing protocol, called Budget Sharing Token protocol (BuST), was proposed to improve the existing timed token approaches in terms of real-time bandwidth guarantee. This paper analyzes the ability of BuST to manage real-time and non real-time traffic under three different budget allocation schemes, and compares the performance of BuST with the original timed-token protocol (FDDI) and its modified version (FDDI-M). It is shown that BuST provides an higher guaranteed bandwidth for real-time traffic than FDDI, and improves the service for non real-time traffic with respect to FDDI-M. Moreover, new properties of the analyzed budget allocation schemes are provided for BuST, FDDI and FDDI-M. Finally, a set of simulation results are carried out to assess the performance of the three considered protocols

Real-Time Resource Reservation Protocol for Wireless Mobile Ad Hoc Networks

Abstract: Wireless communication technology is spreading quickly in almost all the information technology areas as a consequence of a gradual enhancement in quality and security of the communication, together with a decrease in the related costs. This facilitates the development of relatively low-cost teams of autonomous (robotic) mobile units that cooperate to achieve a common goal. Providing real-time communication among the team units is highly desirable for guaranteeing a predictable behavior while operating autonomously in unstructured environments. This paper proposes a MAC protocol for wireless communication that supports dynamic resource reservation for small teams of cooperative robots. The protocol uses a slotted time-triggered medium access transmission control that is collision-free, even in the presence of hidden nodes. The transmissions are scheduled according to the earliest deadline first scheduling policy. An adequate admission control guarantees the timing constraints of the team communication requirements, including when new nodes dynamically join or leave the team. The paper describes the protocol focusing on the consensus procedure that supports coherent changes in the global system. Finally, a set of simulation results are shown that illustrate the effectiveness of the proposed protocol