real time operating systems introduction to real-time systems course originally developed by maj ron...

Real Time Operating Systems

Introduction to

Real-Time SystemsCourse originally developed by

Maj Ron Smith

Apr 20, 2023 1Dr. Alain Beaulieu

Apr 20, 2023 Dr. Alain Beaulieu

Outline

Definitions

Applications of real-time computer

systems

Lifecycles

An Example

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Definitions

Real-Time System:

“A real-time system is a software system that maintains an ongoing and timely interaction with its environment”

Bran Selic

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Definitions (cont’d)

Real-Time System:

“We can think of real-time systems as those that react to external inputs and in a timely manner affect the environment in which they operate”

Burns and Wellings

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Real-Time System:“ any system in which the time at

which output is produced is significant. This is usually because the input corresponds to some movement in the physical world, and the output has to relate to that same movement”The Oxford Dictionary of Computing

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Key characteristics of all the definitions

timeliness timeliness = correctness

interaction with its environment hardware interfaces

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Aren’t all computer systems real-time

While almost all software does interface to hardware, Windows, Icons, Menus and Pointers (WIMP) programming is NOT considered real-time

?

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Hard versus soft real-time hard real-time systems require that strict time

deadlines are met; the strictest are when an event must occur at time x, not just by time x.

in soft real-time systems timeliness of events is important but not necessarily critical.

Often expressed as : x out of y events be on time, or

by x time ± some slack

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Real-time versus embedded software most real-time software is “embedded” within

some larger system, and is usually the de facto central nervous system.

therefore quite often real-time and embedded are used interchangeably when referring to the software of real-time systems.

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Applications of real-time systems

process control nuclear power plant chemical plant

production control automobile assembly line

communication, command & control air traffic control system

embedded systems TV Satellite receiver

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Life Cycles of real-time systems

Small embedded commercial applications typically one-shot

field and (hope to) forget

high multiples cost driven efficiency requirements

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Life Cycles (continued)

Larger real-time systems (including most Military applications)

generally subject to constant change very long life-cycles expensive to maintain robust designs are critical Configuration management is a must Integrated Logistics Support

Software support must be planned

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Examples of Some Real Real-Time systems

Low Level Air Defence ADATS 10 Computers – 10 CSCI (without the missiles)

4 Radar Computers C16A, B, C, D Data Processing Unit Turret Electronic Unit Interface Electronic Unit Coast Mode Processor Control Electronic Unit Servo Electronic Unit

full MIL-STD-2167A

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Apr 20, 2023 Dr. Alain Beaulieu 14

Examples of some Real-Time Systems

InterfaceElec Unit

To Radar and other ADATS (network of 6 +AF-BCP)

Serial Interface& Auto Scanner

R/D Converter16 Channels

ResolversGBA, LOSSA

Discrete I/O24/24 Bits

TEU TAU LEU ECU MV PSSEU

Mount Servo Elect Unit

A/D Converter16 Channels

D/A Converter24 Channels

Analog I/PGBA, LOSSA

Analog O/PSEU

CDU

Main Memory

DPU

CMP

Clock and interrupts16 channel

Apr 20, 2023 15Dr. Alain Beaulieu


Some problems…

Several computer languages, C, Several Assembly Languages, Pascal

DPU was a 16 bit processor… when there was none. 4X4 bit-sliced computer

Cyclic Executive No RTOS End-To-End test two weeks DPU only Cycle counting from Pulse Code

Modulation (PCM) Dumps It works but…

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What might go wrong when developing this type of software?

Requirements formulation / documentation Design formulation / documentation Test formulation / documentation / conduct (Software engineering communication) Schedulability on a single processor Compatibility among systems Support for long-term maintenance

To name just a few

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Summary

“Real-time and distributed systems (combined) design has proven to be one of the most difficult and intricate problems ever faced. This is primarily because of the complexity of the real world in which these systems operate. Their environment can be bewilderingly diverse, dynamic, and unpredictable - components fail at random, communications are corrupted, interruptions occur when they are most inappropriate, and so on.”

Selic

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