Scheduling in time triggered systems under mode changes

Abstract

This thesis presents the use of constraint programming for scheduling tasks in time triggered real time systems undergoing mode changes. The scheduling problem is initially decomposed into schedules for individual modes, and then the schedules generated for each operational mode are processed to maintain timing constraints across mode changes. These mode changes are allowed to occur at particular time instants specified by the designer. A mode change task, in effect, acts as a placeholder for these time instants and different heuristics are proposed to set the period of the mode change tasks. A mode change schedule, which is the new schedule that needs to be executed when a mode change occurs, can be subsequently generated. Constraint programming has previously been used to solve scheduling problems, but until now there have been few attempts to solve the mode change problem using this technique. An example of schedule generation with mode changes in an aircraft control system is shown.