Developing a Complete Integrated Real-Time System

Computing and control engineering journal, 1997

1998

Abstract We present the design and implementation of a soft real time CPU server for the time-sensitive multimedia applications in the Windows NT environment. The server is a user-level daemon process from which multimedia applications can request and acquire periodic processing time in the well-known form of (processing time per period). Our server is based on a careful manipulation of the real time (RT) priority class, and it does not require any modifications to the kernel.

Lecture Notes in Computer Science, 2005

Real-time scheduling is the kernel mechanism having the most impact on RTOS performance. After describing existing algorithms and methodologies for embedded realtime applications, we present their limitations in handling dynamic environments, and discuss new research trends for overcoming them in next generation operating systems. 20.1 Landscape This summary is intended to give a brief overview of the status of scheduling methods, in particular with respect to flexible scheduling. It does not aim to be complete or provide in-depth literature survey. Rather, directions and issues, together with seminal algorithms are presented. Most of the presented algorithms are research prototypes.

Real-Time Systems, 2013

In this work, we provide an experimental comparison between Global-EDF and Partitioned-EDF, considering the run-time overhead of a real-time operating system (RTOS). Recent works have confirmed that OS implementation aspects, such as the choice of scheduling data structures and interrupt handling mechanisms, impact real-time schedulability as much as scheduling theoretic aspects. However, these studies used real-time patches applied into a general-purpose OS. By measuring the run-time overhead of an RTOS designed from scratch, we show how close the schedulability ratio of task sets is to the theoretical hard real-time schedulability tests. Moreover, we show how a well-designed object-oriented RTOS allows code reuse of scheduling components (e.g., thread, scheduling criteria, and schedulers) and easy real-time scheduling extensions. We compare our RTOS to a real-time patch for Linux in terms of the task set schedulability ratio of several generated task sets. In some cases, Global-EDF considering the overhead of the RTOS is superior to Partitioned-EDF considering the overhead of the patched Linux, which clearly shows how different OSs impact hard real-time schedulers.

IEEE Real-Time Systems Symposium, 1985

Process scheduling in real-time systems has almost invariably used one or more of three algorithms: fixed priority, FIFO, or round robin. The reasons for these choices are simplicity and speed in the operating system, but the cost to the system in terms of reliability and maintainability have not generally been assessed. This paper originates from the notion that the primary

2005

This paper will show how advanced embedded realtime systems, with functionality ranging from timetriggered control functionality to event-triggered user interaction, can be made more efficient. Efficient with respect to development effort as well as run-time resource utilization. This is achieved by using a hybrid, static and dynamic, scheduling strategy. The approach is applicable even for hard real-time systems since tight response time guarantees can be given by the response time analysis method for tasks with offsets. An industrial case study will demonstrate how this approach enables more efficient use of computational resources, resulting in a cheaper or more competitive product since more functionality can be fitted into legacy, resource constrained, hardware.

Proceedings 19th IEEE Real-Time Systems Symposium (Cat. No.98CB36279)

This paper focuses on the problem of providing efficient run-time support to multimedia applications in a real-time system, where two types of tasks can coexist simultaneously: multimedia soft real-time tasks and hard real-time tasks. Hard tasks are guaranteed based on worst case execution times and minimum interarrival times, whereas multimedia and soft tasks are served based on mean parameters. The paper describes a server-based mechanism for scheduling soft and multimedia tasks without jeopardizing the a priori guarantee of hard real-time activities. The performance of the proposed method is compared with that of similar service mechanisms through extensive simulation experiments and several multimedia applications have been implemented on the HARTIK kernel.

2010

Hierarchical scheduling frameworks (HSFs) have been devised to support the integration of independently developed and analyzed subsystems. This paper presents an efficient, modular and extendible design for enhancing a real-time operating system with periodic tasks, two-level fixed-priority HSF based on the idling periodic and deferrable servers, and virtual timers. It relies on Relative Timed Event Queues (RELTEQ), a timed event management component targeted at embedded operating systems, which supports long event interarrival time, long lifetime of the event queue, no drift and low overhead. It minimizes the overhead in terms of processor and memory usage, limits the interference of inactive servers on system level, and minimizes the necessary modifications of the underlying operating system. The proposed design was implemented and evaluated within the µC/OS-II real-time operating system used by our industrial and academic partners.

Real-time systems play a considerable role in our society, and they cover a spectrum from the very simple to the very complex. Examples of current real-time systems include the control of domestic appliances like washing machines and televisions, the control of automobile engines, telecommunication switching systems, military command and control systems, industrial process control, flight control systems, and space shuttle and aircraft avionics. All of these involve gathering data from the environment, processing of gathered data, and providing timely response. A concept of time is the distinguishing issue between real-time and non-real-time systems. When a usual design goal for non-real-time systems is to maximize system's throughput, the goal for real-time system design is to guarantee, that all tasks are processed within a given time. The taxonomy of time introduces special aspects for real-time system research. Real-time operating systems are an integral part of real-time systems. Future systems will be much larger, more widely distributed, and will be expected to perform a constantly changing set of duties in dynamic environments. This also sets more requirements for future real-time operating systems. This seminar has the humble aim to convey the main ideas on Real Time System and Real Time Operating System design and implementation.

2020 IEEE 23rd International Symposium on Real-Time Distributed Computing (ISORC), 2020

This paper proposes a novel framework and programming model for real-time applications supporting a declarative access to real-time CPU scheduling features that are available on an operating system. The core idea is to let applications declare their temporal characteristics and/or requirements on the CPU allocation, where, for example, some of them may require real-time POSIX priorities, whilst others might need resource reservations through SCHED_DEADLINE. The framework can properly handle such a set of heterogeneous requirements configuring an underlying multi-core platform so to exploit the various scheduling disciplines that are available in the kernel, matching applications requirements. The framework is realized as a modular architecture in which different plugins handle independently certain real-time scheduling features within the underlying kernel, easing the customization of its behavior to support other schedulers or operating systems by adding further plugins.