Basic Concepts of Real Time Operating Systems

Real-time applications usually are executed on top of a Real-time Operating System (RTOS). Specific scheduling algorithms can be designed. When possible, static cyclic schedules are calculated off-line. If more flexibility is needed on-line techniques are applied. These algorithms are bound to priorities which can be assigned statically or dynamically. Designing a proper RTOS architecture needs some delicate decisions. The basic services like process management, inter-process communication, interrupt handling, or process synchronization have to be provided in an efficient manner making use of a very restricted resource budget. Various techniques like library-based approaches, monolithic kernels, microkernels, or virtual machines/exokernels are applied, based on specific demands. Safety critical application can be supported by separation of applications either in the time or the space domain. Multi-core architectures need special techniques for process management, memory management, and synchronization. The upcoming Wireless Sensor Networks (WSN) generate special demands for RTOS support leading to dedicated solutions. Another special area is given by multimedia applications. Very high data rates have to be supported under (soft) RT constraints. Based on the used encoding techniques (e.g. MPEG) dedicated solutions can be created.