Communicating Embedded Systems: Software and Design

Chapter 1

Models for Real-Time Embedded Systems ¹

1.1. Introduction

The class of real-time embedded systems contains software components that control an application by reacting to stimuli received from a changing environment. Therefore, they are often referred to as reactive systems. The reaction time of these systems must be small enough to cope with the internal dynamics of the controlled or monitored application. They must thus obey the strong timing requirements, and it is crucial to ensure their correctness from both the functional and temporal points of view.

Real-time applications are often regarded as safety critical because their failures may either involve substantial financial losses or endanger human lives. It is also important to detect any error at an early stage to minimize the costs involved in its correction. This issue can be addressed by several approaches. Let us consider the following two approaches: in the first approach, from the application requirements, a model for the application and its expected properties are derived. Then a controller is proposed, using expert knowledge, to restrict the application behavior in order to satisfy the given properties. The next step is to validate the proposed controller using different techniques such as testing, theorem proving, formal verification, etc. If the controller is not acceptable, then it has to be reworked on the basis of the knowledge gained from the reported failures or counter-examples. In the second approach, ...