The paper presents exact schedulability analyses for real-time systems scheduled at run-time with a static priority pre-emptive dispatcher. The tasks to be scheduled are allowed to experience internal blocking (from other tasks with which they share resources) and (with certain restrictions) release jitter — such as waiting for a message to arrive. The analysis presented is more general than that previously published, and subsumes, for example, techniques based on the Rate Monotonic approach. In addition to presenting the theory, an existing avionics case study is described and analysed. The predictions that follow from this analysis are seen to be in close agreement with the behaviour exhibited during simulation studies. 1.

This report extends the current analysis associated with static priority pre-emptive based scheduling to address the wider problem of analysing schedulability of a distributed hard real-time system; in particular it derives analysis for a distributed system where tasks with arbitrary deadlines communicate by message passing and shared data areas. A simple TDMA protocol is assumed, and analysis developed to bound not only the communications delays, but also the delays and overheads incurred when messages are processed by the protocol stack at the destination processor. The report illustrates how a windowbased analysis technique can be used to find the worst-case response times of a distributed task set. An extended example illustrating the application of the analysis is presented.

Power eficient design of real-time embedded systems based on programmable processors becomes more important as system functionality is increasingly realized through software. This pa-perpresents a power optimization method for real-time embedded applications on a variable speed processor: The method com-bines off-line and on-line components. The off-line component determines the lowest possible maximum processor speed while guaranteeing deadlines of all tasks. The on-line component dy-namically varies the processor speed or bring a processor into a power-down mode according to the status of task set in order to exploit execution time variations and idle intervals. Experimen-tal results show that the proposed method obtains a signijicant power reduction across several kinds of applications. 1

AbstractÐIn a hard real-time system, it is assumed that no deadline is missed, whereas, in a soft or firm real-time system, deadlines can be missed, although this usually happens in a nonpredictable way. However, most hard real-time systems could miss some deadlines provided that it happens in a known and predictable way. Also, adding predictability on the pattern of missed deadlines for soft and firm real-time systems is desirable, for instance, to guarantee levels of quality of service. We introduce the concept of weakly hard real-time systems to model real-time systems that can tolerate a clearly specified degree of missed deadlines. For this purpose, we define four temporal constraints based on determining a maximum number of deadlines that can be missed during a window of time �a given number of invocations). This paper provides the theoretical analysis of the properties and relationships of these constraints. It also shows the exact conditions under which a constraint is harder to satisfy than another constraint. Finally, results on fixed priority scheduling and response-time schedulability tests for a wide range of process models are presented.

Due to the critical nature of the tasks in hard real-time systems, it is essential that faults be tolerated. Several studies have shown that space applications, which have very high reliability requirements, have also very high transient faults frequency. Therefore, tolerance to this type of faults is essential in such applications. In this paper, we present a scheme which can be used to tolerate faults during the execution of preemptive real-time tasks. We describe a recovery scheme which can be used to re-execute tasks in the event of single and multiple transient faults and discuss conditions that must be met by any such recovery scheme. We then extend the Rate Monotonic Scheduling (RMS) scheme to provide tolerance for single and multiple transient faults. We derive schedulability bounds for sets of real-time tasks given the desired level of fault tolerance for each task or subset of tasks. Finally, we analyze and compare the bounds derived as a function of the amount of processing ...

Voltage scheduling is indispensable for exploiting the benefit of variable voltage processors. Though extensive research has been done in this area, current processor limitations such as transition overhead and voltage level discretization are often considered insignificant and are typically ignored. We show that for hard, real-time applications, disregarding such details can lead to sub-optimal or even invalid results. We propose two algorithms that guarantee valid solutions. The first is a greedy yet simple approach, while the second is more complex but significantly reduces energy consumption under certain conditions. Through experimental results on both real and randomly generated systems, we show the effectiveness of both algorithms, and explore what conditions make it beneficial to use the complex algorithm over the basic one. 1.

In this paper we present an automated, compiler-based technique to help developers synthesize correct real-time systems. The domain we consider is that of multi-programmed real-time applications, in which periodic tasks control a physical systems via interacting with external sensors and actuators. While a system is up and running, these operations must be performed as specified -- otherwise the system may fail. Correctness depends not only on each program individually, but also on complex task interactions which are usually exposed at runtime. Errors at this point are usually remedied by a costly process of instrumentation, measurement and code tuning. We describe a static alternative to this process, which relies on well-accepted technologies from optimizing compilers and fixed-priority scheduling. Specifically, when an application is found to be overloaded, the scheduling component determines good candidate tasks to get transformed via program slicing. The slicing engine decomposes ...

We describe the design and implementation of a tool for applying rate monotonic scheduling (RMS) technology in distributed environments that serve real-time applications. Our tool, DRMS, enables users to define sets of real-time tasks and the processors to which the tasks will be allocated. The tool finds allocations such that real-time constraints of the tasks are guaranteed. Several feasibility tests can be applied by users in order to evaluate the feasibility of task allocations. Users can vary the descriptions of tasks and processors so that DRMS is a practical tool for designers of real-time systems. Keywords: Deadline, processor allocation, rate monotonic scheduling, real-time systems, scheduling. 1 1 Introduction The correctness of results produced by tasks that execute on a real-time computing system depends on the timeliness of the results in addition to the logical value of the results. A key component of any real-time computing system is the method used to schedu...

Abstract not found

This paper introduces an extension to the RMS scheduling technique that we call "Hot Swapping". Hot Swapping enables a system to choose between various selected implementations of one task on-the-fly and thus to optimize the system's cost (e.g. power savings). The on-the-fly swapping between those implementations requires extra time to save and/or transform states of a certain task implementation. Even if the two steady-state schedules before and after the swapping are feasible, the transient schedule with the additional swapping computation time may exceed the system's capacity. Our technique is an extension to Rate Monotonic Scheduling (RMS). While maintaining and meeting performance requirements, our technique shows an average reduction of 31% in power consumption compared to systems using a pure static scheduling approach (RMS) that cannot make use of task swapping. We have evaluated our algorithm through simulation of five real-world task sets and in addition by use of a large number of generated task sets.