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01-1 EE 4770: Real Time Computing Systems *
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Course: (Spring 1999)
Room 2161 CEBA
Monday Wednesday Friday 8:40-9:30
Call Number 1321
Web Page: http://www.ee.lsu.edu/ee4770
Prerequisite: EE 3750, Microprocessor Systems (or equivalent.).
Offered By:
David M. Koppelman
349 EE Building
(225) 388-5482
koppel@ee.lsu.edu
http://www.ee.lsu.edu/koppel
Monday and Thursday 13:30-16:00 (tentative office hours).
Teaching Assistant:
Jian Zhang
zjian@ee.lsu.edu
Room 150 EE Building, Desk G56.
Office Hours: Mon, Wed 10:30-12:00, Fr 10:30-12:30
Phone: 388-4835.
Graded Material:
40% Midterm Examination.
40% Final Examination. (Cumulative.)
20% Homework.
About one assignment every two weeks.
Lowest homework grade will be dropped.
01-1 EE 4770 Lecture Transparency. Formatted 14:19, 12 January 1999 from lsli0*
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01-2 Real Time Computing System Definition *
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Real Time System (RTS)
A computer-controlled mechanism in which there are strict__ timing____
constraints______on the computer's actions.
Examples:
- Automobile.
- Chemical reactor.
- Home bread maker.
Material to be Covered in The Course
Hardware:
- Sensors.
For detecting light, temperature, etc.
- Conditioning circuits.
For converting sensor output to a useful form.
- Computer-interrupt hardware.
For getting the computer's attention.
Software:
- Real-time software organization and features.
- Estimating timing of RT programs.
- Scheduling RT programs to meet deadlines.
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01-3 Background and Prerequisites *
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Background Needed for Course
Prerequisite: 3750, Microprocessor Systems
Digital logic and computer organization.
Computer programming (no particular language).
Design and analysis of electronic circuits.
Types of Problems to be Assigned
Circuit design. (Design a circuit to meet some specification.)
Explain how a certain part works.
Write pseudocode to perform a certain function.
Types of Problems not__ to be Assigned
Laboratory projects.
Semester-length project.
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01-4 *
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Parts of a Real Time System
A RTS consists of four parts:
- Physical process.
That which is controlled.
- Sensors.
Observe.
- Computer.
That which perceives and plans.
- Actuators.
Act.
: : :for example, consider an anti-lock braking system: : :
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01-5 *
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Anti-Lock Braking System (ABS)
System that controls braking in a car, preventing wheel lock.
Normally, surface of wheels move at same speed as road.
Braking force can cause one or more wheels to slip or lock.
Usually, one wheel will lock before the others.
If ABS detects locking at a wheel it will reduce braking pressure to
stop locking.
ABS as RTS
Physical_process.______
Tire/wheel,
brakes and brake hydraulic system,
car and road, and
driver.
and perhaps the wind.
Sensors.___
Detect speed that wheels are spinning,
force driver exerts on brake pedal,
pressure of brake fluid, etc.
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01-6 *
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Computer______
Hardware: Special embedded microprocessor:
Fewer components needed than general-purpose microprocessor and
made to withstand vibration and temperature extremes.
System Software:
System runs without (computer) operator.
No computer terminal needed.
Easier_ (less hard) to predict timing of software.
Process-Control Software:
Reads wheel speed (and perhaps other data) at regular intervals.
Based on speed of wheels, detects if a wheel is locking.
If so, adjusts pressure of brake fluid.
Actuators_____
Brake-pressure valve.
Dashboard light.
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01-7 *
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Role of Parts of a Real Time System
A RTS consists of four parts:
- Physical process.
That which is controlled by the computer for some productive end.
The thing the computer is controlling.
- Sensors.
Converts state of physical process into information (analog or digital).
Sensors see what's going on.
- Computer.
Based on information from sensors, deduces state of physical process
and issues commands to control the process.
The computer figures out what's going on and issues commands to keep
things running properly.
- Actuators.
In response to commands issued computer, modifies the physical pro-
cess.
Carries out the commands issued by the computer.
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01-8 *
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Other Example Real Time Systems
Washing Machine:
Physical_process:______ (Presumably) dirty clothes, water, detergent, tub,
agitator, etc.
Sensors:___ Water level, water temperature, control panel.
Computer:______Embedded microprocessor.
Computer runs through pre-programmed cycles.
Might modify actions based on water temperature.
Actuators:_____Water valves, tub-rotation motor, and control-panel lights.
Aircraft Autopilot
Performs many functions, for example, maintaining level flight.
Physical_process:______ Airplane, surrounding air, navigation radio sources.
Sensors:___ Airspeed, attitude, control-surface positions, control panel,
etc.
Computer:______Embedded microprocessor or general-purpose computer.
____________________________________________________
_ Great care taken in writing software. _
____________________________________________________ _
Actuators:_____Hydraulics and servos for positioning control surfaces (ruder,
flaps, etc.).
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01-9 *
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Complexity and Reliability
Complexity Range
Very simple: kitchen appliances.
Moderately complex: automobile engine control.
Most complex: aircraft control system, factory assembly line control
system.
Managing the complexity of these systems is a major aspect of RTS de-
sign.
Safety Concerns
People's safety depends on correct functioning of many RTS.
For example, aircraft control systems, automobile control systems,
pharmaceutical-production machinery.
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01-10 *
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Reliability-Assurance Problem
Acceptable error rate must be very low.
Example: if an avionics system causes a plane to crash one out of a mil-
lion landings then how many would die per year?
Testing cannot assure a sufficiently reliable system.
Example: How much would it cost to land an airliner one million times
(to test a device)?
Solutions:
Use proven design methodologies.______
Introduce new techniques slowly.
Design systems to be fault tolerant.
A fault-tolerant system can continue to operate properly despite faults.
Design systems to fail safe.
Failure will result in minimal damage.
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01-11 *
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Challenging (Hard) Part of Real Time Systems
- Writing Specifications for RTS
For large systems this is harder to do than it sounds.
- Writing Software
If can be difficult to ensure that timing deadlines are met under all
circumstances.
- Testing for Bugs in Software
Bugs could result in injury so cannot depend on customers to test
product.
- Evaluating Reliability
This includes software bugs, hardware failure, and specification errors.
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| David M. Koppelman - koppel@ee.lsu.edu | Modified 12 Jan 1999 14:21 (20:21 UTC) |