Chapter 1 Embedded And Real-Time System Department 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

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 method Advantage: priority solved critical fast access to the processor