L1

Question 1

What is a real-time system?

Answer 1

A real-time system is a system that reacts upon ouside events and performs a function based on these and gives a response within a certain time. Correctness of the function does not only depend on correctness of the result, but also the timeliness of it.

Question 2

Classification of real-time systems

Answer 2

Resources
- Enough resources
- System with limited resources

Activation
- Event Trigered (ET) systems
- Time Triggered (TT) systems

Criticality level
- Soft real-time systems
- Hard real-time systems

Applications
- Embedded real-time systems
- Not embedded real-time systems

Question 3

Resources sufficient vs. resource limited systems

Answer 3

Enough resources:

• Can always guarantee the execution of functions whenever they want
• Often safety-critical
• Example: ABS

Limited resources:

• There may be occasions when the system cannot handle all functionality requests
• Main design goal: to work in “normal case”
• Example: Phone systems

Question 4

Event triggered vs Time triggered systems

Answer 4

Event triggered real-time systems:

• External events trigger the execution of a program
• Typically ghrough interrupts
• Example: Phone switches, video on demand

Time triggered real-time systems:

• External events handled at predefined time points
• Often cyclical systems -> repetitive behaviour
• Example: ABS, control systems, manufacturing systems.

Question 5

Hard vs. Soft real-time systems

Answer 5

Hard real-time systems:

• The price for not fulfilling functional ant temporal requirements is very high!
• Failing to fulfil a real-time requirement results in useless omputational result
• OFten safety-critical -> correctness must be verified before the deployment of the system
• Example: ABS, airbag, nuclear power plant

Soft real-time systems

• Occasionally failing to fulfil a time requirement can be accepted
• Usefullness of the computational results is reduced
• Example: booking systems, multimedia

Question 6

Embedded vs. non-embedded real-time system

Answer 6

Embedded RTS

• Integrated in a bigger product
• Difficult to access and re-program
• Example: microwaves ovens, cars, airplanes, medical devices, robots.

Non-embedded RTS

• Based on publically available computers
• Re-programmable on site
• Example: phone systems, industrial control systems, banking systems, internet-based system.

Question 7

Why embedded systems