Chapter 3 - The Basics of Real-time Software (For Mere Mortals)

Abstract

The techniques used in real-time software are just extensions of the stack games played with interrupts. A real-time system allows multiple programs (threads) to be written that look just like conventional programs. A software program that allows the machine resources to be divided among multiple tasks is called a real-time kernel. In most real-time systems, the kernel switches the CPU among tasks so rapidly that all of the tasks appear to be operating simultaneously. A real-time kernel can be extremely simple or quite complex, and if one is working with small microcomputers, the programs can be written in a customized way. There are many ways in which the kernel can interrupt and resume execution of various tasks: the most obvious way is in response to interrupt events. There are several other considerations that need to be taken into account when programming real-time systems. The first danger has to do with interrupt priority. The second potential problem with interrupt procedure originates from the way results are saved.