Patricia Balbastre

Universitat Politècnica de València | UPV · Institute of Industrial Control Systems and Computing (ai2)

There has been a trend towards using multicore platforms for real-time embedded systems due to their high computing performance. In the scheduling of a multicore hard real-time system, there are interference delays due to contention of shared hardware resources. The main sources of interference are memory, cache memory, and the shared memory bus. T...

In multicore scheduling of hard real-time systems, there is a significant source of unpredictability due to the interference caused by the sharing of hardware resources. This paper deals with the schedulability analysis of multicore systems where the interference caused by the sharing of hardware resources is taken into account. We rely on a task m...

In hard real-time embedded systems, switching to multicores is a step that most application domains delay as much as possible. This is mainly due to the number of sources of indeterminism, which mainly involve shared hardware resources, such as buses, caches, and memories. In this paper, a new task model that considers the interference that task ex...

Modern industries require constant adaptation to new trends. Thus, they seek greater flexibility and agility to cope with disruptions, as well as to solve needs or meet the demand for growth. Therefore, smart industrial applications require a lot of flexibility to be able to react more quickly to continuous market changes, offer more personalized p...

Embedded systems used in critical systems, such as aeronautics, have undergone continuous evolution in recent years. In this evolution, many of the functionalities offered by these systems have been adapted through the introduction of network services that achieve high levels of interconnectivity. The high availability of access to communications n...

Hard real-time systems focus on obtaining a feasible schedule while satisfying different temporal requirements. In safety-critical applications, this schedule is generated offline. This article explores different integer linear programming techniques (ILP) to schedule uniprocessor hard real-time systems. The goal is to efficiently obtain a static s...

This paper addresses the problem of energy management of mixed criticality applications in a multi-core partitioned architecture. Instead of focusing on new scheduling algorithms to adjust frequency in order to save energy, we propose a partition to CPU allocation that takes into account not only the different frequencies at which the CPU can opera...

With the ever-increasing industrial demand for bigger, faster and more efficient systems, a growing number of cores is integrated on a single chip. Additionally, their performance is further maximized by simultaneously executing as many processes as possible. Even in safety-critical domains like railway and avionics, multicore processors are introd...

One of the most promising approaches to mixed-criticality systems is the use of multi-core execution platforms based on a hypervisor. Several successful EU Projects are based on this approach and have overcome some of the difficulties that this approach introduces. However, interference in COTS systems due to the use of shared resources in a comput...

This paper presents a hypervisor architecture tailored to low-power real-time applications. This architecture extends the capability of a hypervisor by providing power management techniques and power monitoring services. An implementation based on an existing hypervisor XtratuM that runs over the ARM of a Zynq-7000 SoC device is proposed as a proof...

This paper addresses the problem of energy management of applications in a multi-core partitioned architecture. Instead of focusing on new scheduling algorithms to adjust frequency in order to save energy, we propose a partition to CPU allocation that takes into account the different frequencies at which the CPU can operate. The goal of this paper...

Partitioned systems have emerged as a result of the increasing computer processing power and application complexity and the needs to achieve more secure systems. The use of cache memories into real-time systems has been consolidated in order to mitigate the gap between CPU speed and memory performance. This paper introduces an extended task model i...

Multicore systems are present in many sectors and arriving others, as real-time systems, traditionally reluctant to them due to the difficulty to estimate worst case execution time in multicore platforms. However, partitioned systems integrated by a partitioning kernel and a set of partitions with different levels of criticality is one of the emerg...

Schedulability analysis of hierarchical real-time systems is based in the previous knowledge of the scheduling algorithms both in the local and the global levels. In a partitioned system with safety and security issues and certification assurance levels, the global scheduling is usually generated using a static table. Therefore, each partition must...

Multi-core processors are increasingly being considered to provide the performance required by future safety critical systems. In some domains like space, it is specially significant due to the processor technology frequency is limited by the presence of radiation. In that case, the way to increase computing power can be achieved by the use of mult...

The complexity of industrial embedded systems is increasing continuously. Companies try to keep a leading position by offering additional functionalities and services. Systems are to be composed by multiple sensor, actuation and computation subsystems running in a coordinated way on a distributed platform. Due to the increment in processor power, i...

XtratuM is an open source hypervisor that uses para-virtualization techniques designed to comply with safety critical real-time requirements. Several projects aimed to define a reference architecture for space on-board systems have adopted XtratuM as a virtualization layer in order to enforce the strong spatial and temporal isolation between softwa...

In this paper a new task model with periods defined as ranges is proposed with the main goal of drastically reducing the hyperperiod of the task set. The model is focused to be applied in cyclic scheduling, where the length of the major cycle of the plan is determined by the hyperperiod. But it also can be applied in synthetic task sets generation,...

This paper presents a computational model for parti-tioned systems. The computational model has as goal a goal a particular way of conceptualizing computations and temporal constraints and predetermines the tech-niques to be used to analyse the schedulability of the sys-tem. The model is based on the entities used to specify the systems.

Partitioned software architectures represent the future of secure systems. They have evolved to fulfill security and avionics requirements where predictability is extremely important. The idea behind a partitioned system is the virtualization. A virtual machine (VM) is a software implementation of a machine that executes programs like a real machin...

In this paper a new task model with periods defined as ranges is proposed with the main goal of drastically reduce the hyperperiod of the task set. The model is focused to be applied in cyclic scheduling, where the length of the major cycle of the plan is determined by the hyperperiod. But it also can be applied in synthetic task sets generation, w...

The ARINC 653 APEX (Application/Executive), also referred to as the ARINC 653 API, is a software specification for space and time partitioning in Safety-critical avionics Real-time operating systems. This interface provides the services to build partitioned systems and has been used successfully in avionic systems. Now, it has been a focus of atten...

Current trends in the development of industrial applications enforce the use of wireless networks to communicate the system nodes mainly to increase flexibility and reliability of these applications and to reduce the implementation cost. However, in control applications, as consequence of the latency and jitter generated by the network, not always...

Hypervisor is a promising technology to build partitioned systems. However, it has to be adapted and customized to the requirements of the target application. Hypervisors are small software layers which can be designed to meet real-time and security properties. Its correctness can be sufficient to ensure the security of the system as a whole or, at...

Actualmente existe un gran interés por el desarrollo de aplicaciones industriales utilizando redes inalámbricas, principalmente por el aumento de la flexibilidad del sistema y la disminución de los costos de implementación. Sin embargo, los retrasos y el jitter que introduce la red de comunicaciones en las aplicaciones de control, han dado lugar a...

ARINC 653 defines a partitioned frame-work where the partitions are scheduled according to a predefined cyclic plan and the processes of each partition are scheduled with a fixed priority policy. The timing characteristics defined in ARINC (period and duration) can hardly be used to precisely repre-sent the timing requirements of the applications....

Existe una separación entre la fase de diseño del regulador y su implementación en el computador de forma que, cada fase asume simplificaciones sobre la otra fase, lo cual lleva a un comportamiento inesperado o incorrecto del sistema a controlar. Desde hace algunos años, han surgido diversos trabajos que han apuntado la falta de integración de las...

Hierarchical scheduling has recently been used to provide temporal isolation to embedded virtualised systems. Response time analysis is a common way to derive a schedulability test for these systems. This paper points out that response time analysis for hierarchical fixed-priority scheduling found in the literature is only exact for tasks of the hi...

In the design of a real-time application it is fundamental to know how a change in the task parameters would affect the feasibility of the system. Relaxing the classical assumptions on static task sets with fixed periods and deadlines can give higher resource utilisation and better performance. But the changes on task parameters have to be done alw...

Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with a very large bound. In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented...

Nowadays, systems often integrate a variety of applications whose service requirements are heterogeneous. Consequently, systems must be able to concurrently serve applications which rely on different constraints. This raises the problem of the dynamic distribution of the system resources (CPU, memory, network, etc.). Therefore, an integrated Qualit...

Real-time systems are often designed using a set of periodic tasks. Task periods are usually set by the system requirements, but deadlines and computation times can be modified in order to improve system performance. Sensitivity analysis in real-time systems has focused on changes in task computation times using fixed priority analysis. Only a few...

Dynamic memory storage has been widely used for years in computer science. However, its use in real-time systems has not been considered as an important issue, and memory management has not receive much consideration, whereas today's real-time applications are often characterized by highly fluctuating memory requirements. In this paper we present a...

Feasibility tests for hard real-time systems provide information about the schedulability of the task set. However, this information is a yes or a no answer, that is, whether the task set achieves the test or not. From the real-time system design point of view, having more information available would be useful. For example, how much the computation...

A modern control system is typically implemented as a multitasking software application executing in a real-time operating system. If the computer load is high, the controller will experience delays and jitter, which in turn degrade the control performance. Arguing for an integrated design approach, the paper describes two computer tools for implem...

The design of embedded control systems should be addressed in both the controller definition and its implementation. While the design of the controller is based on control theory, the implementation is designed by assuming the principle that control loops can be modeled and implemented as periodic activities. Periodic activities that can be organis...

Real-time systems are often designed using a set of periodic tasks. Task periods are usually set by the system requirements, but deadlines and computation times can be modified in order to improve system performance. Sensitivity analysis in real-time systems has focused on changes in task computation times using fixed priority analysis. Only a few...

The real-time implementation of a controller typically introduces artefacts like delay and jitters that have not been considered at the design stage. As a consequence, the system behaves in a non-periodic manner, and the real performance is degraded with respect to the expected response. This paper proposes a hybrid task model to reduce the impact...

Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed...

In this paper we present a new algorithm for CPU resource reservation in real-time systems that allows the coexistence of hard, soft and non real-time tasks. The proposed algorithm is specifically designed to handle computational overload. A task that needs more CPU-time than reserved can reuse the spare bandwidth, without interfering with the othe...

Feasibility tests for hard real-time systems provide information about the schedulability of a set of tasks. However, this information is a yes or no answer whether the task set achieves the test or not. From the system design point of view, it would be useful to have more information, for example, how much can one vary some task parameters, such a...

Linux has been effectively used as a reliable operating system in workstations and servers. However, the interest for using it in embedded systems has grown recently, due to the easiness for customizing it and the availability of the source code. This paper describes the experience of customizing RT-Linux for its use in an embedded real-time contro...

Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, this two phases have been developed in separate ways. Recently, some works have pointed...

Control applications require defining several parallel activities to model the environment. Periodic tasks model the activities to be executed at periodic instants of time. While the process of control design is focused on obtaining the regulator, later on translated into an algorithm, the software design is focused on producing pieces of software...

Dynamic priority scheduling theory is mature enough to be used in real-time systems. This paper describes the modifications done to the current RTLinux code to provide both fixed and dynamic priority scheduling. Since the CSP protocol (PTHREAD PRIO PROTECT) can only be used in fixed priority schedulers, a more suitable type of mutex has been implem...

In the framework of real-time digital control, two fundamental parameters are defined, the control effort and the control action interval. The first one is related to the strength of the control that, due to the intersampling open-loop control, determines the degrading of performances under unexpected delays. The second one refers to the unavoidabl...

Industrial application of digital control requires the synergy between well designed control algorithms and carefully implemented control systems. The control performances can be strongly influenced depending on the data acquisition and control action delays. The paper shows how to evaluate these delays (jitter) under static or dynamic scheduling p...

This paper reviews our experience in the laboratory of two courses in the Control Engineering Curriculum at the Politechnical University of Valencia: Real-time Systems and Distributed Control Systems. These courses, in a Control Engineering curriculum, require the development of industrial prototypes to validate different aspects of the system deve...

Resumen En el presente artículo se describe una herramienta software de soporte a la docencia de asignaturas relacionadas con sistemas de tiempo real. Con ella se pretende que el alumno sea capaz por si mismo de encontrar las diferencias entre los sistemas operativos de propósito general y los que están diseñados para soportar tareas o procesos de...

The current trend in the development of Networked Control Systems (NCS) is the use of wire-less networks to communicate the system nodes, which have been called Wireless Sensors and Actuators Networks (WSAN). This trend is principally to increase flexibility and reliability of these applications and to reduce the implementation cost. Several protoc...

Scheduling theory has shown an impressive evolution due to the intensive research done in this area. As a result, a lot of scheduling algorithms has been proposed to support a large amount of applications. RTLinux uses a xed-priorit y scheduler and although xed-priorit y scheduling is suited for a large number of real-time applications, it has some...

En el diseño de una aplicación de tiempo real es fundamental conocer como un cambio en los parámetros temporales de las ta- reas afecta a la planificabilidad del sistema. El análisis de sensi- bilidad permite conocer el rango de periodos, plazos y tiempos de cómputo que hacen al conjunto de tareas planificable. El análi- sis de sensibilidad de peri...

Resumen Este trabajo presenta la experiencia de realizar trabajos basados en sistemas empotrados, para la asignaturas relacionadas con sistemas de tiempo real. Las herramientas software utilizadas para el desarrollo de los trabajos son el lenguaje de programación Ada'95 y el microkernel de tiempo real MarteOS desarrollado en la Universidad de Canta...

The ARINC-653 standard defines a general-purpose APEX (APpli-cation/EXecutive) interface between the Operating System (O/S) of an avion-ics computer resource and the application software. This interface provides the services to build partitioned systems and has been used successfully in avionic systems. In recent years, the space domain is consider...