Page 52 - DCAP608_REAL TIME SYSTEMS

Unit 4: A Reference Model of Real-time Systems

Questions: Notes
1. Comment upon the statement: “A virtual campus is a complex task involving many
different aspects of higher education administration and instructional delivery”.

2. What is the transmission systems meant for?
3. How does information are exchanged in a traditional classroom.

Source: http://www.westga.edu/~distance/aoki13.html

4.5 Summary

 A reference model of real-time systems is needed to focus on aspects of the system relevant
to its real-time timing and resource properties.

 A system may be characterized by 3 models.
 A workload model describing the applications.
 A resource model describing the system resources.

 The scheduling and resource management algorithms that define how the application
uses the resources.
 Resources always mean a re-usable resource.

 Each computation or data transmission that is executed repeatedly at regular or semi-
regular time intervals in order to provide a function of the system is modelled as a period
task.

 A periodic task occurs at regular intervals.
 A task is aperiodic if the jobs in it have either soft deadlines or no deadlines.
 The jobs are said to have precedence constraints if they are constrained to execute in some
order.
 If the jobs can execute in any order, they are said to be independent.
 Data dependency cannot be captured by a precedence graph.

4.6 Keywords

Aperiodic Task: A task is aperiodic if the jobs in it have either soft deadlines or no deadlines.
Periodical Task Model: The periodic task model is a well-known deterministic workload model.
Resource Model: A resource model describes the system resources available to the applications.
Sporadic Tasks: Tasks containing jobs that are released at random time instants and have hard
deadlines are sporadic tasks.
Transmission Link: A transmission link connecting an on-board flight management system to
the ground controller is a different type of processor from the link connecting two air traffic
control centres.
Workload Model: Workload model is the model that describes the applications supported by
the system.

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