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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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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
- Real Time systems must satisfy explicit (bounded) response-time constraints or risk failure
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
- 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
RTOS
- Real Time Operating Systems
- A Powerful Partioning Tool
- Manages Resources
- Manages Conflicts
- Aids in partioning problems
Resources
- Tasking and Scheduling - Actions
- ISR Support - Hardware Interface
- Semaphores- Communication
- Mailboxes - Communication
- Queues - Communication
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
- 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
- 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 - ISR/Asynchronous events
- (Also called Interrupt Level)
- Background - “infinite loop” that calls modules to perform desired functions
- (Also called Task Level)
