Papers by Rômulo de Oliveira
Often, many control applications with time restrictions are implemented by the codification of co... more Often, many control applications with time restrictions are implemented by the codification of complex programs in assembly language, programming timers, manipulating peripheral devices, tasks and interruption priorities in low level. The consequence of this approach is that the control software is produced by ad hoc techniques that can present low reliability and high cost. The design and implementation of an embedded realtime control system uses, basically, two types of professionals: the control engineer and the software engineer. The main tool used by the control engineer is the functional blocks diagram that, mapped to diagrams of components, supply the software engineer with the necessary information, but the simple use of functional blocks generates a monotasking system. This article describes a proposal that aims to improve the process of construction (design and implementation) of embedded systems with functional blocks diagram using the multitasking model. In this sense, the work consisted, mainly, of the multitasking framework proposal and the development of a real-time operational microkernel to support the developed framework. This work contributes to the improvement of software development processes for embedded systems in the context of control and automation.
The complexity increase and variety of equipments controlled by embedded computers generate the n... more The complexity increase and variety of equipments controlled by embedded computers generate the need of a multidisciplinary approach for the process of development of those equipments, involving the areas of software, mechanics, electric and electronic engineering. System engineering uses different techniques to concurrently integrate these different views. In this sense, it is being specified by OMG a modeling language, denominated SysML (System Modeling Language). It intends to include in a single specification an integrated view of the system, one that includes hardware, software and electro-mechanics parts. The objective of this paper is to do an empirical evaluation of the modeling language SysML, in the sense of identifying its capacities and its limitations for the modeling of embedded systems. For that purpose, an electronic fuel injection system developed by Department of Automation and Systems at our university will be used.
Sistemas de tempo real se caracterizam pela necessidade de correção temporal em suas execuções. U... more Sistemas de tempo real se caracterizam pela necessidade de correção temporal em suas execuções. Usualmente, esses sistemas são implementados usando tecnologias e plataformas proprietárias que aumentam seus custos de desenvolvimento e manutenção. Recentemente, tem aumentado o interesse de executar sistemas distribuídos de tempo real, usando tecnologias abertas (tais como Internet e CORBA). Essa tendência tem demandado esforços complementares tanto no sentido de se obter suportes de execução previsíveis utilizando sistemas abertos, como também no sentido de se estabelecer modelos e abordagens de tempo real mais flexíveis e que considerem a possibilidade de ocorrência de sobrecargas. Este artigo apresenta a abordagem de escalonamento adaptativo (p+i,k)-firm para aplicações distribuídas de tempo real. A abordagem lida com condições de sobrecarga, objetivando uma degradação suave, através da combinação da técnica da computação imprecisa com a garantia (m,k)-firm.
The development process of complex systems needs to take in account differents domains and aspect... more The development process of complex systems needs to take in account differents domains and aspects. SysML (Systems Modeling Language) is a new modeling language that allows a system description with various integrated diagrams (as structure, behavior and requirements diagrams), but SysML lacks formality for the requirement verification. The aim of this paper is to propose an approach to verify complex systems using SysML as a language which describes the system structure and requirements. Petri nets and temporal logic LTL are used respectively to formalize the system behavior and requirements. The benefit of such formalization is to allow an automatic formal verification. In order to demonstrate this methodology, it will be used a factory automation system, modeled by SysML and Petri nets, and verified by the TINA toolbox.
Recentemente, existe um interesse crescente em modelos de sistemas de tempo real e abordagens fle... more Recentemente, existe um interesse crescente em modelos de sistemas de tempo real e abordagens flexíveis de escalonamento para lidar com situações de sobrecarga transientes, que podem ocorrer em ambientes não deterministas. Este artigo apresenta a abordagem de escalonamento (p+i,k)-firm, voltada sistemas de tempo real. A abordagem lida com situações de sobrecarga através da combinação da técnica da computação imprecisa com a garantia (m,k)-firm.
Resumo: Ao longo de mais de 40 anos, sistemas operacionais têm sido desenvolvidos com o propósito... more Resumo: Ao longo de mais de 40 anos, sistemas operacionais têm sido desenvolvidos com o propósito de tornar a utilização do computador mais eficiente e mais conveniente. Para isso, um enorme número de conceitos, abstrações, mecanismos e algoritmos foram criados e aprimorados. Este artigo é um tutorial a respeito das técnicas fundamentais empregadas nos sistemas operacionais contemporâneos. Também são discutidos aqui os sistemas operacionais distribuídos e de tempo real.
Sistemas computacionais de tempo real são identificados como aqueles submetidos a requisitos de n... more Sistemas computacionais de tempo real são identificados como aqueles submetidos a requisitos de natureza temporal. Este trabalho descreve a técnica de Computação Imprecisa, uma abordagem proposta para o escalonamento de sistemas tempo real. São apresentadas motivações para o seu emprego e as formas básicas de programação. São também discutidos os diferentes objetivos de escalonamento propostos na literatura para este tipo de abordagem. Finalmente, diversos algoritmos de escalonamento são descritos e classificados.
In recent years, the FlexRay communication protocol has been promoted as a de facto standard for ... more In recent years, the FlexRay communication protocol has been promoted as a de facto standard for in-vehicular communications. In the FlexRay protocol, the communication timeline is organized as a sequence of four segments, whereas the static segment defines a set of slots specifically designed for the transmission of synchronous messages. In this paper, we investigate the following problem:
A redução do preço de computadores e sua grande disseminação vêm impulsionando a criação de redes... more A redução do preço de computadores e sua grande disseminação vêm impulsionando a criação de redes de computadores. Hoje, essas redes estão em todos os lugares, e a Internet pode ser entendida como um grande e disperso sistema distribuído, que permite aos seus usuários o acesso a uma variedade de serviços. São múltiplos os desafios enfrentados pelos projetistas desses sistemas -frente aos problemas de heterogeneidade, segurança e confiabilidade.
Industrial automation systems may include people, hardware, software and others necessaries to pr... more Industrial automation systems may include people, hardware, software and others necessaries to produce the desirable results. The SysML modeling language is being proposed, by OMG and INCOSE, as a language that allows the system description correctly and consistently among various participants of the same project (software, mechanical, electrical and others engineers). The objective of this work is to evaluate the SysML proposal as a description language for industrial systems through the modeling of an industrial automation experimental unit. A brief system description of the case study will be made, the SysML diagrams will be presented during the system modeling and finally the comments and considerations about the models and the modeling task.
The industrial automation systems can include people, hardware, software and others ways necessar... more The industrial automation systems can include people, hardware, software and others ways necessaries to produce the desirable results. The SysML modeling language is being proposal, by the OMG and the INCOSE, as the language that goes to allow the systems description correctly and consistently between various participants of the same project (software, mechanics, electricians and others engineers). The objective of this work is to evaluate the SysML proposal as a description language for industrial systems through the modeling of an industrial automation experimental unit.
Real-time systems grow in complexity and applicability each day. The development of these systems... more Real-time systems grow in complexity and applicability each day. The development of these systems through component-based approaches has proved to be a promising alternative. This paper aims a qualitative comparison between the proposals found in the literature, placing them in the real-time context, and presenting some gaps to be explored by the research community. We also propose the adoption of dynamic guarantee in real-time component-based systems through the implementation of an acceptance test in component containers.
This paper presents a design pattern of an adaptive scheduling based on the management of the tas... more This paper presents a design pattern of an adaptive scheduling based on the management of the tasks execution time, achieved through multiple versions of the tasks, applied to the Real-Time Specification for Java. A structure of classes is used to facilitate the development of tasks, while allowing the independence of the application code from the code responsible for the adaptive control. The design pattern is described through UML diagrams and an example implementation is presented.
O objetivo deste artigo é comparar a meta-heurística Busca Tabu com uma heurística simples na res... more O objetivo deste artigo é comparar a meta-heurística Busca Tabu com uma heurística simples na resolução do problema de alocação e escalonamento de blocos funcionais em barramentos de campo que seguem a especificação Foundation Fieldbus. Nas experiências são empregados cenários baseados em aplicações reais de controle distribuído.
A new concept for road intersections is proposed based on Intelligent Transportation Systems (ITS... more A new concept for road intersections is proposed based on Intelligent Transportation Systems (ITS) technology. It consists of the substitution of the semaphores currently in use by a Centralized Vehicular Controler (CVC), which controls the acceleration and steering of vehicles approaching an automated intersection. The CVC is able to make vehicles cross in narrower gaps than those achievable by man-guided vehicles, thus minimizing the bottleneck effect caused by confict resolution at the intersection. Application of the CVC in an intersection with two conflicting approaches with arrival patterns following a modified exponential distribution is examined. Control is accomplished by a vehicle-delay minimization algorithm. Simulation results show the capacity increase granted by the CVC in relation to intersections with semaphores.
The Distributed Real-Time Thread is an emergent concept for distributed real-time systems. Distri... more The Distributed Real-Time Thread is an emergent concept for distributed real-time systems. Distributed Threads are schedulable entities with an end-to-end deadline that transpose nodes, carrying their scheduling context. Mechanisms for predicting the missing of deadlines are fundamental because corrective actions can be incorporated for improving system quality of service. In this work we propose an end-to-end deadline missing prediction mechanism called Available Remaining Slack (ARS). Simulations show that the proposed prediction mechanism presents good results for improving the overall performance and availability of distributed real-time systems.
In this paper, adaptive scheduling based on dynamic priorities and imprecise computation is used ... more In this paper, adaptive scheduling based on dynamic priorities and imprecise computation is used in web servers. The goal is to keep proportional differentiation services. An approach with admission control has its properties of controllability and predictability evaluated. Another contribution is to show how to use and implement this approach in Apache web servers.
This article presents the results of a case study related to the application of a method for calc... more This article presents the results of a case study related to the application of a method for calculating the response time of the WorldFIP fieldbus network used as the communication support for the process level of a large hydroelectrical generator control system. Two alternatives of the network bus arbiter table assembling criteria are considered: one adopts the Rate Monotonic scheduling algorithm (RM), based on static priorities, traditionally employed by the industry; the other one employs the Earliest Deadline First algorithm (EDF), based on dynamic priorities.
In the mobile agent area, as part of an agent mission, it may exist the necessity of meeting a fi... more In the mobile agent area, as part of an agent mission, it may exist the necessity of meeting a firm end-to-end deadline, although with some itinerary flexibility due to some optional resources. In this paper it is adopted an execution model where agents do not previously know their itineraries. The objective is to propose and evaluate heuristics for agent routing.
The mobile agent technology is an important research area in the scope of code mobility. As part ... more The mobile agent technology is an important research area in the scope of code mobility. As part of an agent mission objective, it may exist the necessity of meeting an end-to-end deadline, although with some flexibility about the itinerary the agent should follow. The objective of this paper is to define an execution model for mobile agents that include timing constraints. We also show some simple heuristics that are able to guide these agents in the itinerary definition, considering the existence of an endto-end deadline for the mission.
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Papers by Rômulo de Oliveira