Effective Real-Time Computing on Linux

Real-time Systems, 1999

This paper describes an open system architecture that allows independently developed hard real-time applications to run together and supports their reconfiguration at run-time. In the open system, each real-time application is executed by a server. At the lower level, the OS scheduler schedules all the servers on the EDF basis. At the upper level, the server scheduler of each server schedules the ready jobs of the application executed by the server according to the algorithm chosen for the application. The paper describes the two-level CPU scheduling scheme used by the open system and the design and implementation of a uniprocessor open system within the framework of the Windows NT operating system. The implementation consists of three key components: the two-level hierarchical kernel scheduler, common system service providers, and real-time application programming interface.

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.

Real-Time Systems, 2002

This paper presents a framework appropriate for Flexible Real-Time Systems (FRTS) and a run-time support system based on that framework, called Flexible Real-Time Linux (FRTL). The framework proposes to build each task as a sequence of mandatory and optional components and to separate their execution in two scheduling levels. This approach is shown to provide both hard guarantees and¯exible behavior. The FRTL system has been implemented by enhancing the original capabilities of Real-Time Linux (RT-Linux), while maintaining its predictability and ef®ciency features. This paper also shows a complete schedulability test on which all sources of overhead of the FRTL itself have been introduced. By applying this complete test, the designer is able to safely guarantee a real-time application running on the FRTL system. a special task without timing constraints but which can be executed if suf®cient resources are detected at run-time. While hard tasks implement predictable (and normally simple) algorithms due to their timing constraints, optional components can implement highly complex, unbounded algorithms 1 . Optional components may therefore be used to enhance the response quality achieved by hard tasks. In particular this framework proposes both a computational model on which hard tasks consist of a sequence of mandatory and optional components and a software architecture on which mandatory and optional components are separated in two scheduling levels. Mandatory components are scheduled, at the real-time level, according to a ®xed priority preemptive scheme; this permits their execution to be guaranteed by using a feasibility test . Optional components are scheduled inside the non-real-time level, which is executed in slack time . This level schedules optional components by means of a utility-based scheduling policy (not imposed by the framework) by which it is possible to add¯exibility to the scheduling process. The architecture also proposes a strict hierarchy between both levels, by which the real-time level always decides when to run and when to preempt the nonreal-time level. By means of this hierarchical organization, the two scheduling policies are not mixed but combined, having a clearly de®ned, simple interface. This provides three interesting advantages: ®rst, the schedulability impact of scheduling decisions at the nonreal-time level is eliminated, making the system more robust and simpler to analyze. Second, the real-time level is liberated from the signi®cant overhead that utility-based policies usually provide. Third, the designer is facilitated in incorporating a custom, application-speci®c scheduling policy within the non-real-time level.

2002

A Ana, por su eterna (im)paciencia, y en memoria de nuestro amigo Lucas I have never begun a novel with more misgiving. If I call it a novel it is only because I don't know what else to call it. I have little story to tell and I end neither with a death nor a marriage.

2010

The goal of this paper is to present and compare two different Linux extensions for making Real-time Linux solutions. The idea is to use and adapt general purpose operating systems to provide a real-time environment which is comparable to specialized RTOS. In this paper Xenomai and RTAI are present.

1992

Real-time operating system services are required to support multimedia systems that rely heavily of the workstation processor for control of the audio and video processors and movement of audio and video data. Such services are typically not available in existing workstation operating systems. This note comments on the requirements for such services and briefly describes the YARTOS kernel; an operating system kernel that provides real-time communication and computation services.

Annual Review in Automatic Programming, 1981

The operating system kernel of a multiprocessor system based on 16 bit microcomputers is described. The multiprocessor system constitutes a node of a local computer network dedicated to the control of continuous or discontinuous industrial processes. The kernel makes available a virtual machine where processes allocatedon dif ferent processors are executed in parallel, while processes which reside on the same processor are executed in a multitasking environment. The processes can cooperate by means of synchronization and message passing primitives; furthermore they can interact by means of short-term scheduling primitives which perform the creation, destruction, activation and termination of a process. The interprocessor communication mechanisms allow the primitives to make all the process interactions transparent to the physical allocation of the interacting processes. The system has been completely implemented in the PASCAL language, excepting only few functions of the lowest level, coded in the assembler language. The distributed kernel has been developed and tested on a conventional machine (a DEC PDP11/34 computer under RSXll-M Operating System). The processes allocated on the same processor have been implemented as a sil gle RSXll task, and interprocessor communications have been simulated by means of intertask system primitives.

2001

finished. It is possible to avoid the problem by adding break points to the event handling code where the handling of urgent events can take place. On the other hand, the problem is not critical, if a powerful processor is available. The real-time properties of most embedded systems are based on the use of real-time operating systems. Application of such operating systems requires high expertise and much time. The resulting software is often heavy and hard to maintain. In this paper we present a class of application specific operating systems called ReaGOS. ReaGOS is based on a new architecture and an operating principle, where the operating system calls application programs but not vice versa. The new architecture saves both data and code memory and it is fast enough for embedded systems. The operating system is generated automatically from a high level graphical specification. Another method uses interrupt mechanisms to handle I/O driver events [5]. This method has some disadvanta...

EURASIP Journal on Embedded Systems, 2008

The rapid progress in processor and sensor technology combined with the expanding diversity of application fields is placing enormous demands on the facilities that an embedded operating system must provide.

Operating systems have become a key factor for the success of today’s mobile devices. With the rising capabilities of the underlying hardware, the complexity of managing these capabilities grows similarly. In the last years, multi-core hardware has been a major challenge for operating systems and it starts to shape also the real-time subdomain. These challenges, along with one of the best solution for managing complex resource allocations – called hierarchical scheduling – are briefly presented in the Introduction part of this paper. Related work done in the domains of real-time operating systems, multi-core resource allocation and hierarchical scheduling is presented from both the commercial/industrial and the research/academic points of view. The next section is introducing the heterogeneous multi-core platform that will be used for running the real-time operating system proposed in this paper, which is described in detail in section IV. The way the operating system is managing th...