What is a real-time system?
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.
Classification of real-time systems
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
Resources sufficient vs. resource limited systems
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
Event triggered vs Time triggered systems
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.
Hard vs. Soft real-time systems
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
Embedded vs. non-embedded real-time system
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.
Why embedded systems
