Книга: Real-Time Concepts for Embedded Systems

14.1 Introduction

14.1 Introduction

Many activities need to be completed when designing applications for real-time systems. One group of activities requires identifying certain elements. Some of the more important elements to identify include:

1. system requirements,

2. inputs and outputs,

3. real-time deadlines,

4. events and event response times,

5. event arrival patterns and frequencies,

6. required objects and other components,

7. tasks that need to be concurrent,

8. system schedulability, and

9. useful or needed synchronization protocols for inter-task communications.

Depending on the design methodologies and modeling tools that a design team is using, the list of steps to be taken can vary, as well as the execution order. Regardless of the methodology, eventually a design team must consider how to decompose the application into concurrent tasks (Step 7).

This chapter provides guidelines and discussions on how real-time embedded applications can be decomposed. Many design teams use formalized object-oriented development techniques and modeling languages, such as UML, to model their real-time systems initially. The concepts discussed in this section are complementary to object-oriented design approaches; much emphasis is placed on decomposing the application into separate tasks to achieve concurrency. Through examples, approaches to decomposing applications into concurrent tasks are discussed. In addition, general guidelines for designing concurrency in a real-time application are provided.

These guidelines and recommendations are based on a combination of things-lessons learned from current engineering design practices, work done by H. Gomaa, current UML modeling approaches, and work done by other researchers in the real-time field. Our guidelines provide high-level strategies on proceeding with decomposing real-time applications for concurrency. Our recommendations, on the other hand, are specific strategies focusing on the implementation of concurrency. Both the guidelines and recommendations might not necessarily cover every exception that can arise when designing a real-time embedded application. If two guidelines or recommendations appear to contain opposing thoughts, they should be treated as constituting a tradeoff that the designer needs to consider.

At the completion of the application decomposition process, robust systems must validate the schedulability of the newly formed tasks. Quantitative schedulability analysis on a real-time system determines whether the system as designed is schedulable. A real-time system is considered schedulable if every task in the system can meet its deadline.

This chapter also focuses on the schedulability analysis (Step 8). In particular, the chapter introduces a formal method known as Rate Monotonic Analysis (RMA).

Оглавление книги