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Realizing Changes of Operational Modes with a Pre

Run-Time Scheduled Hard Real-Time System

Gerhard Fohler?

Institut f?ur Technische Informatik
Technische Universit?at Wien
Treitlstr. 3/182
A-1040 Wien, Austria
[email protected]


Most hard real-time computer systems control processes that undergo several, mutually exclusive modes of operation. This paper discusses issues of handling mode changes and requirements for their application. Specification of mode changes, construction of static schedules for modes and transitions, and run-time execution of mode changes are presented. We propose concepts for mode changes in the context of MARS, a pre run-time scheduled hard real-time system. Our methods adhere closely to the ones established for single modes.

By decomposing the system into a set of disjoint modes, the design process and its comprehension are facilitated, testing efforts are reduced significantly, and solutions are enabled which do not exist if all system activities of all modes are combined into a single schedule.

1 Introduction

Processes controlled by hard real-time systems1 typically exhibit mutual exclusive phases of operation and control. Such systems require a pre run-time verification, so that all ?This work has been supported in part by ESPRIT Basic Research Action No. 3092 - Predictably Dependable Computer Systems and the Austrian Science Foundation (Fonds zur F?orderung der wissenschaftlichen Forschung) under contract P8002-TEC.
This paper is published in Proceedings of the Second International Workshop on Responsive Computer Systems, Saitama,Japan, October 1992, Springer Verlag.
1By hard real-time system we mean a system in which catastrophic consequences can be adjudged to be due to timing failures, as defined in [7]