From the Publisher:
Real-Time Systems is both a valuable reference for professionals and an advanced text for Computer Science and Computer Engineering students. 

Real world real-time applications based on research and practice

State-of-the-art algorithms and methods for validation

Methods for end-to-end scheduling and resource management

More than 100 illustrations to enhance understanding

Comprehensive treatment of the technology known as RMA (rate-monotonic analysis) methods

A supplemental Companion Website www.prenhall.com/liu

http://user.it.uu.se/~yi/courses/rts/dvp-rts-08/notes/Course-INFO.pdf

Real-Time Systems

In general computing systems, a job (process/task) may suspend itself whilst it is waiting for some activity to complete, eg, an accelerator to return data In real-time systems, such self-suspension can cause substantial performance/schedulability degradation This observation, first made in 1988, has led to the investigation of the impact of self-suspension on timing predictability, and many relevant results have been published since Unfortunately, as it has recently come to light, a number of the existing results are flawed To provide a correct platform on which future research can be built, this paper reviews the state of the art in the design and analysis of scheduling algorithms and schedulability tests for self-suspending tasks in real-time systems We provide (1) a systematic description of how self-suspending tasks can be handled in both soft and hard real-time systems; (2) an explanation of the existing misconceptions and their potential remedies; (3) an assessment of the influence of such flawed analyses on partitioned multiprocessor fixed-priority scheduling when tasks synchronize access to shared resources; and (4) a discussion of the computational complexity of analyses for different self-suspension task models

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Many suspensions, many problems: a review of self-suspending tasks in real-time systems

Techniques originating from the Internet of Things (IoT) and Cyber-Physical Systems (CPS) areas have extensively been applied to develop intelligent and pervasive systems such as assistive monitoring, feedback in telerehabilitation, energy management, and negotiation. Those application domains particularly include three major characteristics: intelligence, autonomy and real-time behavior. Multi-Agent Systems (MAS) are one of the major technological paradigms that are used to implement such systems. However, they mainly address the first two characteristics, but miss to comply with strict timing constraints. The timing compliance is crucial for safety-critical applications operating in domains such as healthcare and automotive. The main reasons for this lack of real-time satisfiability in MAS originate from current theories, standards, and technological implementations. In particular, internal agent schedulers, communication middlewares, and negotiation protocols have been identified as co-factors inhibiting the real-time compliance. This paper provides an analysis of such MAS components and pave the road for achieving the MAS compliance with strict timing constraints, thus fostering reliability and predictability.

The challenge of real-time multi-agent systems for enabling IoT and CPS

Multi-Agent Systems (MAS) technology is widely used for the development of intelligent distributed systems that manage sensitive data (e.g., ambient assisted living, healthcare, energy trading). To foster accountability and trusted interactions, recent trends advocate the use of blockchain technologies (BCT) for MAS. Although most of these approaches have only started exploring the topic, there is an impending need for establishing a research road-map, as well as identifying scientific and technological challenges in this scope. As a first necessary step towards this goal, this paper presents a systematic literature review of studies involving MAS and BCT as reconciling solutions. Aiming at providing a comprehensive overview of their application domains, we analyze motivations, assumptions, requirements, strengths, and limitations presented in the current state of the art. Moreover, discussing the future challenges, we introduce our vision on how MAS and BCT could be combined in different application scenarios.

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Multi-Agent Systems and Blockchain: Results from a Systematic Literature Review

Many real-time systems include tasks that need to suspend their execution in order to externalize some of their operations or to wait for data, events or shared resources. Although commonly encountered in real-world systems, study of their timing analysis is still limited due to the problem complexity. In this paper, we invalidate a claim made in one of the earlier works [1], that led to the common belief that the timing analysis of one self-suspending task interacting with non-self suspending sporadic tasks is much easier than in the periodic case. This work highlights the complexity of the problem and presents a method to compute the exact worst-case response time (WCRT) of a self-suspending task with one suspension region. However, as the complexity of the analysis might rapidly grow with the number of tasks, we also define an optimization formulation to compute an upper-bound on the WCRT for tasks with multiple suspendion regions. In the experiments, our optimization framework outperforms all previous analysis techniques and often finds the exact WCRT.

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Timing Analysis of Fixed Priority Self-Suspending Sporadic Tasks

Computing platforms are evolving towards heterogeneous architectures including processors of different types and field programmable gate arrays (FPGAs), used as hardware accelerators for speeding up specific functions. The increasing capacity and performance of modern FPGAs, with their partial reconfiguration capabilities, have made them attractive in several application domains, including space applications.This paper proposes a framework for supporting the development of safety-critical real-time systems that exploit hardware accelerators developed through FPGAs with dynamic partial reconfiguration capabilities.A model is first presented and then used to derive a response-time analysis to verify the schedulability of a real-time task set under given constraints and assumptions. Although the analysis is based on a generic model, the proposed framework has been conceived to account for several real-world constraints present on today's platforms and has been practically validated on the Zynq platform, showing that it can actually be supported by state-of-the-art technologies. Finally, a number of experiments are reported to evaluate the worst-case performance of the proposed approach on synthetic workload.

A Framework for Supporting Real-Time Applications on Dynamic Reconfigurable FPGAs

In recent years, there has been a growing interest in supporting component-based software development of complex real-time embedded systems. Techniques such as machine virtualisation have emerged as interesting mechanisms to enhance the security of these platforms, while real-time scheduling techniques have been proposed to guarantee temporal isolation of different virtualised components sharing the same physical resources. This combination also highlighted criticalities due to overheads introduced by hyper-visors, particularly for low-end embedded devices. This led to the need of investigating deeper into solutions based on lightweight virtualisation alternatives, such as containers. In this context, this paper proposes to use a real-time deadline-based scheduling policy built into the Linux kernel to provide temporal scheduling guarantees to different co-located containers. The proposed solution extends the SCHED_DEADLINE scheduling policy to schedule Linux control groups, allowing user threads to be scheduled with fixed priorities inside the control group scheduled by SCHED_DEADLINE. The proposed mechanism can be configured via control groups, and it is compatible with commonly used tools such as LXC, Docker and similar. This solution is compatible with existing hierarchical real-time scheduling analysis, and some experiments demonstrate consistency between theory and practice.

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Container-based real-time scheduling in the Linux kernel

Heterogeneous computing platforms including both processors and field programmable gate arrays (FPGAs) represent an attractive solution for balancing software flexibility with high performance and energy efficiency of custom hardware modules. Furthermore, the dynamic partial reconfiguration (DPR) capabilities of modern FPGAs allow virtualizing the available area to support several hardware modules in time sharing, hence making them even more attractive. Such a feature is exploited by the FRED framework, recently proposed to support the development of real-time applications upon such platforms. This paper presents an implementation of the FRED framework for the Linux operating system over the Zynq-7000 platform produced by Xilinx. Design solutions for managing hardware accelerators are first discussed. Then, a software architecture for Linux is presented, which comprises (i) support for shared-memory communication with hardware accelerators, (ii) an improved driver to handle the FPGA reconfiguration and (iii) a scheduler for requests of hardware acceleration. The proposed solution allows exploiting the enormous number of software systems available for Linux (such as drivers, libraries, communication stacks, etc.) and the typical programming flexibility of software, while relying on predictable hardware acceleration of heavy computations.

A Linux-based support for developing real-time applications on heterogeneous platforms with dynamic FPGA reconfiguration

Robots interacting with human beings are widespread in modern environments, and those performing intelligent tasks without human supervision need to take into account potential criticalities. Making robots compete enable their evaluation with respect to navigation, mapping, object recognition, tracking and manipulation capabilities. Robot competitions date back to the early '80s proving to be useful for educational and research purposes. Several competitions are focused on human-robot interaction, even though they rarely produce as outcome robots capable to seamlessly interact with human beings. The main reason for this is the lack of understanding of human intentions and the failure to rapidly react to human actions. In other words, an ideal robot must be able to communicate and coordinate with humans or with other robots, to act autonomously, and to react under real-time constraints. This paper proposes a new framework to simplify the development of intelligent robots, testing them in a real robot competition. The framework combines (i) a multi-agent system to interact with humans, other robots and perform object identification and pathfinding, and (ii) a real-time motion control deployed on the Erika RTOS, to move the robot and react in a timely fashion to changes in the environment. In the considered competition scenario, the robot is required to identify and collect common objects in a bounded arena with dynamic obstacles in a limited amount of time, receiving commands from humans and competing with other robots. This approach confirms the powerful combination of multi-agent systems, computer vision, and real-time systems.

A framework based on real-time OS and multi-agents for intelligent autonomous robot competitions

The increasing complexity of embedded systems requires an improved capability of detecting and fixing errors. The availability of a modeling environment like Simulink allows the verification by simulation or model checking of system properties and of the correct behavior of the design. This verification is possible upon condition that the requirements are expressed in a formal way. Test and verification in Simulink is often a time-consuming process that requires the systems developers to translate requirements in model blocks for the verification. The capability of performing such translation is seldom available and prone to translation and interpretation errors. We present in this paper a monitor generation tool and a Simulink library that enable a methodology to translate requirements in structured natural language into formal Signal Time Language (STL) constraints, leading to the automatic generation of Simulink monitors that check at run-time the desired properties. The tool automatically creates and connects the monitor blocks to a target Simulink model.

Alessio Balsini

Papers

A Framework for Supporting Real-Time Applications on Dynamic Reconfigurable FPGAs

Container-based real-time scheduling in the Linux kernel

A Linux-based support for developing real-time applications on heterogeneous platforms with dynamic FPGA reconfiguration

A framework based on real-time OS and multi-agents for intelligent autonomous robot competitions

Generation of simulink monitors for control applications from formal requirements