Capturing periodic concurrent interactions of mission computer tasks

Safety critical systems, such as aviation systems controlled by software, often have hard real-time requirements. Producing the correct result at the right time is the fundamental goal of such systems. Formally specifying the system functions and the timing requirements is the crucial step towards achieving such a goal. Aviation systems often need to be modified or upgraded on a regular basis, i.e. functionality and timing constraints may be altered. Therefore, the formal specification of such systems needs to be easily reused, maintained and modified. This paper demonstrates how the task scheduling aspects of an aircraft mission computer can be formalised in TCOZ.