Schedulability analysis of fixed priority preemptive scheduled systems can be performed by calculating the worst-case response-time of the involved processes. The system is deemed schedulable if the calculated responsetime for each process is less than its corresponding deadline. It is desirable that the Response-Time Analysis (RTA) can be efficiently performed. This is particularly important in dynamic real-time systems when a fast response is needed to decide whether a new job can be accommodated, or when the RTA is extensively applied, e.g., when used to guide the heuristics in a higher level optimiser. This paper presents a set of methods to improve the efficiency of RTA calculations. The methods are proved correct, in the sense that they give the same results as traditional (non-improved) RTA. We also present an evaluation of the improvements, by applying them to the particularly time-consuming traffic model used in RTA for ATM communication networks. Our evaluation shows that the proposed methods can give an order of magnitude reduction of the execution time of RTA.

The schedulability analysis of Controller Area Network (CAN) developed by the research community is able to compute the response times of CAN messages that are queued for transmission periodically or sporadically. However, there are a few high-level protocols for CAN such as CANopen and Hägglunds Controller Area Network (HCAN) that support the transmission of mixed messages as well. A mixed message can be queued for transmission both periodically and sporadically. Thus, it does not exhibit a periodic activation pattern. The existing analysis of CAN does not support the analysis of mixed messages. We extend the existing analysis to compute the response times of mixed messages. The extended analysis is generally applicable to any high level protocol for CAN that uses any combination of periodic, event and mixed (periodic/ event) transmission of messages.

In this article we give an overview of the Worst-Case Execution Time (WCET) analysis research performed by the WCET group of the ASTEC Competence Center at Uppsala University. The basis for this work is our modular architecture for a WCET tool, used b oth to identify the components of the overall WCET analysis problem, and as a starting point for the development of an industry strength WCET tool prototype. Within this framework we have proposed solutions to several key problems in WCET analysis, including representation and analysis of the control ow of programs, modeling of the behavior and timing of pipelines and other low-level timing aspects, integration of the control ow information and low-level timing to obtain a safe and tight WCET estimate, and validation of our tools and methods. We have focussed on the needs of embedded realtime systems in designing our tools and directing our research. Our long-term goal is to provide WCET analysis as a part of the standard tool chain for embedded development (together with compilers, debuggers, and simulators). This is substantially facilitated by our close cooperation with the embedded systems programming-tools vendor IAR Systems.

The Hierarchical Scheduling Framework (HSF) has been introduced as a design-time framework to enable compositional schedulability analysis of embedded software systems with real-time properties. In this paper, a software system consists of a number of semi-independent components called subsystems. Subsystems are developed independently and later integrated to form a system. To support this design process, in the paper, the proposed methods allow non-intrusive configuration and tuning of subsystem timing-behavior via subsystem interfaces for selecting scheduling parameters. This paper considers three methods to handle overruns due to resource sharing between subsystems in the HSF. For each one of these three overrun methods corresponding scheduling algorithms and associated schedulability analysis are presented together with analysis that shows under what circumstances one or the other is preferred. The analysis is generalized to allow for both Fixed Priority Scheduling (FPS) and Earliest Deadline First (EDF) scheduling. Also, a further contribution of the paper is the technique of calculating resource-holding times within the framework under different scheduling algorithms; the resource holding times being an important parameter in the global schedulability analysis.

Abstract