1. Introduction to Realtime Systems (& Embedded Systems)
B. Ramamurthy
9/19/2018

2. The course will enable you to:
Identify the unique characteristics of real-time systems
Explain the general structure of a real-time system
Define the unique design problems and challenges of real-time systems
Apply real-time systems design techniques to various software programs.
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3. For embedded systems it will enable you to
Understand the basics of an embedded system
Program an embedded system
Design, implement and test an embedded system.
Ex: realtime + embedded : games on a Gameboy or arcade games
Ex: realtime: Tetris on a laptop
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4. Example real-time systems
Domain
Application
Avionics
Navigation; displays
Multimedia
Games; simulators
Medicine
Robot surgery; remote surgery; medical imaging
Industrial systems
Robot assembly lines; automated inspection
Civilian
Elevator control
Automotive system; Global positioning system (GPS)
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5. Lets discuss some realtime system (RTS) characteristics
Realtime response
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6. Realtime Characteristics
RTS have to respond to events in a certain pre-detemined amount of time.
The time constraints have to be considered during planning, design, implementation and testing phases.
Internal failures due to software and hardware fault have be handled satisfactorily.
You cannot simply pop-up a dialog box that says “send report” or “don’t send report”.
Also external failures due to outside sources need to be handled.
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7. Realtime Characteristics (contd.)
Typical interaction in an RTS is asynchronous. Thus an RTS should have features to handle asynchronous events such as interrupt handlers and dispatcher and associated resources.
Potential for race condition: when state of resources are timing dependent race condition may occur.
Periodic tasks are common.
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8. Embedded System
Is a special purpose system designed to perform a few dedicated functions.
Small foot prints (in memory)
Highly optimized code
Cell phones, mp3 players are examples.
The components in an mp3 player are highly optimized for storage operations. (For example, no need to have a floating point operation on an mp3 player!)
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9. Real-time system concepts: Ch.1
A system is a mapping of a set of input into a set of outputs.
A digital camera is an example of a realtime system: set of input including sensors and imaging devices producing control signals and display information.
Realtime system can be viewed as a sequence of job to be scheduled.
Time between presentation of a set of inputs to a system and the realization of the required behavior, including availability of all associated outputs, is called the response time of the system.
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10. Real-time system concepts (contd.)
Real-time system is the one in which logical correctness is based on both the correctness of the output as well as their timeliness.
A soft real-time system is one in which performance is degraded by failure to meet response-time constraints.
A hard real-time system is one in which failure to meet a single deadline may lead to complete and catastrophic failure.
More examples:
Automatic teller: soft
Robot vacuum cleaner: firm
Missile delivery system: hard
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11. Determinism
In every system, and particularly in an embedded system maintaining control is extremely important.
Example: (i) a two wheeler going our of control on certain maneuvers. (ii) wheel locks when you enter an unsafe state.
It is desirable to avoid such states thorugh proper design.
As far as possible, we would like the realtime system to be deterministic.
A system is deterministic, if for each possible state and each set of inputs, a unique set of outputs and next state can be detremined.
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12. CPU Utilization
Utilization%
Zone type
Type of application
0-25
CPU under utilized
General purpose
25-50
Very safe ,,
51-68
Safe 69
Theoretical limit
Embedded system
70-82
Questionable
83-99
dangerous
CPU utilization or time loading factor, U, is a measure of the percentage of non-idle processing.
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13. CPU Utilization (Contd.)
Let fi be the frequency of a periodic task.
Then period pi = 1/ fi
Let ei be the execution time of the task.
Then overall utilization of the CPU is:
U =
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14. Sample real-time systems
Lets discuss the sample systems listed in the text books.
We will also go over the exercises at the end of chapter 1.
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15. 9/19/2018

16. Realtime system characteristics
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