KERNEL DESIGN ISSUES - Hard Real-Time Computing Systems: Predictable Scheduling Algorithms and Applications - page 349

10

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 applica-
tions. For educational purposes, we illustrate the structure and the main components
of a small real-time kernel, called DICK ( DI dactic CK ernel), mostly written in C
language, which is able to handle periodic and aperiodic tasks with explicit time con-
straints. The problem of time predictable intertask communication is also discussed,
and a particular communication mechanism for exchanging state messages among pe-
riodic tasks is illustrated. Finally, we show how the runtime overhead of the kernel
can be evaluated and taken into account in the schedulability analysis.

10.1 STRUCTURE OF A REAL-TIME KERNEL

A kernel represents the innermost part of any operating system that is in direct con-
nection with the hardware of the physical machine. A kernel usually provides the

following basic activities:

Process management,

Interrupt handling, and

Process synchronization.

Process management is the primary service that an operating system has to provide.
It includes various supporting functions, such as process creation and termination, job
scheduling, dispatching, context switching, and other related activities.