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Publications

2017

Schedulability Analysis for Global Fixed-Priority Scheduling of the 3-Phase Task Model

Authors
Maia, C; Nelissen, G; Nogueira, L; Pinho, LM; Perez, DG;

Publication
2017 IEEE 23RD INTERNATIONAL CONFERENCE ON EMBEDDED AND REAL-TIME COMPUTING SYSTEMS AND APPLICATIONS (RTCSA)

Abstract
Scheduling real-time applications on general purpose multicore platforms is a challenging problem from a timing analysis perspective. Such platforms expose uncontrolled sources of interference whenever concurrent accesses to memory are performed. The non-deterministic bus and memory access behavior complicates the estimations of applications' worst-case execution times (WCET). The 3-phase task model seems a good candidate to circumvent the uncontrolled sources of interference by isolating concurrent memory accesses. A task is divided in three successive phases; first, the task loads its instruction and data in a local memory, then it executes non-preemptively using those pre-loaded instructions and data, and finally, the modified data are pushed back to main memory. Following this execution model, tasks never access the bus during their execution phase. Instead, all the bus accesses are performed during the first and third phases. In this paper, we focus on the global fixed-priority scheduling of the 3-phase task model. A new schedulability test is derived by modelling the interference happening on the bus rather than the interference on the cores as in the state-ot-the-art techniques. The effectiveness of the test is evaluated by comparing it against the state-of-the-art.

2017

Modelling and Simulation Perspective in Service Design

Authors
Dragoicea, M; Falcao e Cunha, J; Alexandru, MV; Constantinescu, DA;

Publication
Handbook of Research on Strategic Alliances and Value Co-Creation in the Service Industry - Advances in Hospitality, Tourism, and the Services Industry

Abstract

2017

Metalearning

Authors
Brazdil, P; Vilalta, R; Giraud Carrier, CG; Soares, C;

Publication
Encyclopedia of Machine Learning and Data Mining

Abstract
In the area machine learning / data mining many diverse algorithms are available nowadays and hence the selection of the most suitable algorithm may be a challenge. Tbhis is aggravated by the fact that many algorithms require that certain parameters be set. If a wrong algorithm and/or parameter configuration is selected, substandard results may be obtained. The topic of metalearning aims to facilitate this task. Metalearning typically proceeds in two phases. First, a given set of algorithms A (e.g. classification algorithms) and datasets D is identified and different pairs < ai,dj > from these two sets are chosen for testing. The dataset di is described by certain meta-features which together with the performance result of algorithm ai constitute a part of the metadata. In the second phase the metadata is used to construct a model, usually again with recourse to machine learning methods. The model represents a generalization of various base-level experiments. The model can then be applied to the new dataset to recommend the most suitable algorithm or a ranking ordered by relative performance. This article provides more details about this area. Besides, it discusses also how the method can be combined with hyperparameter optimization and extended to sequences of operations (workflows).

2017

Identification of Dynamic Simulation Models for Variable Speed Pumped Storage Power Plants

Authors
Moreira, C; Fulgencio, N; Silva, B; Nicolet, C; Beguin, A;

Publication
HYPERBOLE SYMPOSIUM 2017 (HYDROPOWER PLANTS PERFORMANCE AND FLEXIBLE OPERATION TOWARDS LEAN INTEGRATION OF NEW RENEWABLE ENERGIES)

Abstract
This paper addresses the identification of reduced order models for variable speed pump-turbine plants, including the representation of the dynamic behaviour of the main components: hydraulic system, turbine governors, electromechanical equipment and power converters. A methodology for the identification of appropriated reduced order models both for turbine and pump operating modes is presented and discussed. The methodological approach consists of three main steps: 1) detailed pumped-storage power plant modelling in SIMSEN; 2) reduced order models identification and 3) specification of test conditions for performance evaluation.

2017

The model-based disturbance rejection with MOMI tuning method for PID controllers

Authors
Vrancic, D; Oliveira, PM; Cvejn, J;

Publication
Lecture Notes in Electrical Engineering

Abstract
The paper presents a tuning method for PID controllers which substantially improves closed-loop disturbance rejection performance while keeping the tracking performance. The tuning method is based on the internal disturbance compensator which parameters are calculated according to the Magnitude Optimum criterion. The results of experiments show that the proposed model-based approach gives superior disturbance-rejection response and lower controller activity when compared to Disturbance Rejection Magnitude Optimum tuning method. © Springer International Publishing Switzerland 2017.

2017

Combining Dataflow Applications and Real-time Task Sets on Multi-core Platforms

Authors
Ali, HI; Akesson, B; Pinho, LM;

Publication
SCOPES

Abstract
Future real-time embedded systems will increasingly incorporate mixed application models with timing constraints running on the same multi-core platform. These application models are dataflow applications with timing constraints and traditional real-time applications modelled as independent arbitrary-deadline tasks. These systems require guarantees that all running applications execute satisfying their timing constraints. Also, to be cost-efficient in terms of design, they require efficient mapping strategies that maximize the use of system resources to reduce the overall cost. This work proposes an approach to integrate mixed application models (dataflow and traditional real-time applications) with timing requirements on the same multi-core platform. It comprises three main algorithms: 1) Slack-Based Merging, 2) Timing Parameter Extraction, and 3) Communication-Aware Mapping. Together, these three algorithms play a part in allowing mapping and scheduling of mixed application models in embedded real-time systems. The complete approach and the three algorithms presented have been validated through proofs and experimental evaluation. © 2017 Copyright held by the owner/author(s).

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