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Myths and Realities of Real-Time Linux Software Systems

Publisher: VersaLogic Corp.

Format: PDF
Date: 2009-08-04

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VersaLogic Corp.
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Overview:
This paper addresses some of the differences between real-time and general purpose operating systems, including an analysis of several common misconceptions including performance issues, latency, hard vs. soft real-time systems, programming APIS and software kernel. A definition for real-time operating systems (RTOS) is provided, along with an example of an RTOS, and a list of the important metrics that help to quantify a real-time system. Some of the important characteristics of an RTOS are compared with those of a general-purpose operating system (GPOS), and the applications of RTOS are listed in the form of a table. The paper also details the fundamental approaches to making the Linux kernel real-time, presenting an overview of the PREEMPT_RT patch, and covering the issues related to device drivers that can be used with the real-time kernel (PREEMPT_RT patch).

TABLE OF CONTENTS
1.	What Is a Real-Time System?	1
1.1.	Analogy for Real-Time Systems	1
2.	Metrics of Real-Time	2
2.1.	Interrupt Latency	2
2.2.	Scheduling Latency	2
2.3.	Worst-Case Latency	3
2.4.	Latency Requirements	4
3.	Hard Vs. Soft Requirements	4
3.1.	Hard Real-Time	4
3.2.	Soft Real-Time	4
4.	GPOS vs. RTOS	4
5.	Myths of Real-Time: Real-Time = Performance?	5
6.	Who Needs Real-Time?	5
7.	Real-Time in Linux	6
7.1.	Advantages of the PREEMPT_RT Approach	7
7.2.	Is the PREEMPT_RT Patch a Hard Real-Time or Soft Real-Time System?	7
7.3.	Overview of PREEMPT_RT Patch	7
8.	Device Drivers and the PREEMT_RT Patch	8
9.	References	9
10.	Tables
10.1.	GPOS and RTOS Systems	4
10.2.	Applications of RTOS	6