Real Time Systems

Introduction

Characteristics of real time operating system
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Process scheduling - Priority based
Resource access control - Aim is to keep the duration of every priority inversion bounded from above.
Memory allocation/deallocation - Memory fragmentation may cause indeterminism. Use preallocated buffers.

Does real-time mean as fast as possible?
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The term "real-time" does not mean "as fast as possible" but rather "real-time" demands consistent, repeatable, known timing performance.


Resource access control (Chapter 8 of book Real Time Systems by Jane W. S. Liu)

Nonpreemptive Critical Section (NPCS) Protocol
Priority-Inheritance Protocol
Basic Priority-Ceiling Protocol

Differences between priority-inheritance protocols and priority-ceiling protocol
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Priority-inheritance rule of these are essentially same
The priority-inheritance protocol does not prevent deadlock.
Priority-ceiling blocking is sometimes referred to as avoidance blocking - blocking caused by the priority ceiling rule is the cost for avoidance of deadlocks among jobs.
Priority-inheritance is greedy while later is not.



Few Terms/Concepts

Priority-inversion
Priority ceiling of a resource
Priority ceiling of a system



Books/Articles/Links


"Tutorial on Hard Real-Time Systems", edited by John A. Stankovic and Krithi Ramamritham, IEEE Computer Society reprint series, Computer Society order number 819


Basic Concepts of Real-Time Operating Systems


Comp.RealTime NewsGroup FAQ
http://www.faqs.org/faqs/realtime-computing/faq/

Books --