Heuristic techniques for allocating and scheduling communicating periodic tasks in distributed real-time systems

This paper deals with the problem of pre-runtime allocating and scheduling communicating periodic tasks in a distributed real-time system. The task system is modeled with independent periodic macro-tasks. The physical architecture consists of a network of identical monoprocessor sites, fully connected by a bus. Two medium access control protocols are considered : CSMA/CA and TDMA. Our objective is to find an allocation of tasks to sites and a subsequent schedule for them such that the periodicity and precedence constraints are satisfied. Besides dealing with these constraints (which is often the sole concern of many studies), the effective communication delays due to the message scheduling and the bus access control protocol are taken into account when the task schedule is being built. Two algorithms for solving this problem are presented: a clustering algorithm and a genetic algorithm.