In this paper we describe a language for defining scheduling algorithms for hard real-time systems and a tool to simulate the behavior of such systems on a predefined task set. The language is suited for describing a real-time system composed of a task set, resources and a scheduling algorithm. The tasks can either be periodic or aperiodic, dependent or independent and the time constraints (e.g. deadlines) may be soft or hard. We consider two types of resources: the cpu and semaphores. Semaphores are used to describe the various possible dependences of the task set: shared memory, inter-task communication, devices,... We consider only mono-processor real-time systems. The third part of the system is given by the scheduling algorithm which is used to give resources (cpu and semaphores) to tasks.