TABLE OF CONTENTS Simple software applications are typically designed to run sequentially , one instruction at a time, in a pre-determined chain of instructions. However, this scheme is inappropriate for real-time embedded applications, which generally handle multiple inputs and outputs within tight time constraints. Real-time embedded software applications must be designed for concurrency.
Concurrent design requires developers to decompose an application into small, schedulable, and sequential program units. When done correctly, concurrent design allows system multitasking to meet performance and timing requirements for a real-time system. Most RTOS kernels provide task objects and task management services to facilitate designing concurrency within an application.
This chapter discusses the following topics:
task definition,
task states and scheduling,
typical task operations,
typical task structure, and
task coordination and concurrency.
A task is an independent thread of execution that can compete with other concurrent tasks for processor execution time. As mentioned earlier, developers decompose applications into multiple concurrent tasks to optimize the handling of inputs and outputs within set time constraints.
A task is schedulable. As Chapter 4 discusses, the task is able to compete for execution time on a system, based on a predefined scheduling algorithm. A task is defined by its distinct set of parameters and supporting data structures. Specifically, upon creation, each task has an associated name, a unique ID, a priority (if part of a preemptive scheduling plan), a task control block (TCB), a stack, and a task routine, as shown in Figure 5.1). Together, these components...
