an overview of real time operating systems
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An Overview of Real Time Operating Systems. John C. Shovic. What is a Real Time System?. A system where timeliness is as important as the correctness of the outputs Real Time systems may not be “Fast” systems

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what is a real time system
What is a Real Time System?
  • A system where timeliness is as important as the correctness of the outputs
  • Real Time systems may not be “Fast” systems
  • Real Time systems must satisfy explicit (bounded) response-time constraints or risk failure
real time software
Real Time Software
  • Complexity of real time software is enormous
  • Building “polling” software that can do everything is complicated and when it needs to be changed, it’s very difficult
more definitions
More Definitions
  • Embedded System - Software system completely encapsulated by the hardware it controls
  • Organic System - Software system that is not highly dependent on the hardware and has a generalized user interface
  • Semi-detached system - Software system that has attributes of both embedded and organic systems
slide5
RTOS
  • Real Time Operating Systems
    • A Powerful Partioning Tool
    • Manages Resources
    • Manages Conflicts
    • Aids in partioning problems
resources
Resources
  • Tasking and Scheduling - Actions
  • ISR Support - Hardware Interface
  • Semaphores- Communication
  • Mailboxes - Communication
  • Queues - Communication
actions and rtos
Actions and RTOS

Queue

Data

Monitor

Errors

Print

Manage

Paper

RTOS

tasks threads and processes
Tasks, Threads and Processes
  • Task = Process - Independently executing entity that may control resources. May contain multiple threads
  • Thread - A path through the code - A task may have multiple threads iff each thread has own data area
task swapping
Task Swapping
  • Co-operative - The task gives up control
  • Time-Slice - Context switcher shares time
  • Preemptive - context switcher shares time, budgeting both on fairness and dynamic task priorities
real time concepts
Real-Time Concepts
  • Doing Hard Time - Tasks have to be performed correctly and on time
  • Doing Soft Time - Tasks have to be done as fast as possible, but not on a specific time
  • Most systems are mixes
foreground background
Foreground/Background
  • Foreground - ISR/Asynchronous events
    • (Also called Interrupt Level)
  • Background - “infinite loop” that calls modules to perform desired functions
    • (Also called Task Level)
foreground background systems
Foreground/Background Systems

Background

Foreground

ISR

ISR

ISR

Time

ISR

Code Execution

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