Chapter 1 Embedded And Real-Time System Department of Computer Science Hsu Hao Chen Professor...
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Transcript of Chapter 1 Embedded And Real-Time System Department of Computer Science Hsu Hao Chen Professor...
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
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