Kernel Design Issues

In this chapter, we present some basic issues that should be considered during the design and the development of a hard real-time kernel for critical control applications. For didactical purposes, we illustrate the structure and the main components of a small real-time kernel, called DICK (DIdactic CKernel), mostly written in C language, which is able to handle periodic and aperiodic tasks with explicit time constraints. The problem of time-predictable intertask communication is also discussed, and a particular communication mechanism for exchanging state messages among periodic tasks is illustrated. Finally, we show how the runtime overhead of the kernel can be evaluated and taken into account in the schedulability analysis.