Modeling and scheduling real-time control systems with relative consistency constraints

Control applications control and monitor an external physical environment. Process control and manufacturing systems are examples of such applications. In such systems the temporal relationship between the external environment and the control system plays an important role. In this paper, the temporal relationship of data within the control system and the external environment, known as data temporal consistency, is considered. First the control system is modeled as a graph of periodic tasks. Then the problem of scheduling a set of periodic tasks on a uniprocessor with the relative consistency as a scheduling constraint is studied and its computational complexity is investigated. A novel aspect of the scheduling problem is with respect to the scheduling constraints. More precisely, it is shown how the relative phasing of a periodic task is constrained by the relative phasings of its predecessor tasks