Chapter 1

Embedded And Real-Time SystemDepartment of Computer Science

Hsu Hao Chen

Professor Hsung-Pin Chang

Outline

What is an embedded system ？ Characteristics of embedded systems Real-time systems concept Real-time operating systems and real-

time kernels Processes, tasks, and threads Architecture of real-time systems

What is an embedded system ？ For practical purposes Embedded system consisting of a

compact, fast, and extremely reliable operating system

Microprocessor located inside a device

Embedded system is a collection of programs that run under operating system

Characteristics of embedded systems(1/2)

Virtually all kinds of computing systems

Temporal determinism Time required to process any task is

finite and predictable Less concerned with average response

time than worst-case response time Must have a guarantee on the upper

time limit

Characteristics of embedded systems(2/2)

It is typically encapsulated by the hardware it controls, so end-users are unaware of its presence

It is actually a computer system that does not have the outward appearances of a computer system.

Real-time systems concept Operate within specified time

constraints System must respond to inputs or

events within prescribed time limits Real-time constraints:

Hard Real-Time Example: air traffic control system.

Soft Real-Time Example: PS2

Real-time operating systems and real-time kernels

Kernel

Other RTOS services

RTOS kernel

Processes, tasks, and threads

Program

Process

Program

Thread 1 Thread 2 Thread n…Figure 1.2 Comparison of processes and threads

Architecture of real-time systems(1/2)

Threads are process two common architecture Control loop with polling

Polling of the kernel executes an infinited loop

Advantage:easy to implement

Disadvantage:difficult to give threads with critical fast access to the processor

Architecture of real-time systems(2/2)

Preemptive scheduling method ThreadX use is preemptive scheduling metho

dAdvantage:

priority solved critical fast access to the processor