Question

1. Provide an example of a real-time application and, to the best of your knowledge, discuss its following aspects:

1. What would be the involved periodic tasks? What would be their release time (or release-time jitter)?
2. What would be the aperiodic tasks in the application? What would be their release time, i.e., events that would trigger the aperiodic tasks?
3. What would be the sporadic tasks in the application? What would be their release time, i.e., events that would trigger the aperiodic tasks?

Answer 1

a.

Periodic Task in the application
As the name suggests periodic tasks are type of tasks that work on the regular intervals.
*Phase of the task. Phase is release time of the first job in the task. If the phase is not mentioned then release time of first job is assumed to be zero.
*Period of the task i.e. the time interval between the release times of two consecutive jobs.
*Execution time of the task.
*Relative deadline of the task.

Release Time
*Sometimes actual release time of a job remains unknown.
*Only know that ri is in a range [ ri-, ri+ ],This range is known as release time jitter.
*Here "ri" is how early a job can be released and "ri+" is how late a job can be released.
Only range [ ei-, ei+ ] of the execution time of a job is known.   
*Here "ei" is the minimum amount of time required by a job to complete its execution and
"ei+" the maximum amount of time required by a job to complete its execution.

Real time example is,
Consider the task Ti with period = 5 and execution time = 3
Phase is not given so, assume the release time of the first job as zero. So the job of this task is first released at t = 0 then it executes for 3s and then next job is released at t = 5 which executes for 3s and then next job is released at t = 10. So jobs are released at t = 5k where k = 0, 1, . . ., n

b.

Aperiodic Task in the application

*Aperiodic task is a part of dynamic task
*In this type of task, jobs are released at arbitrary time intervals that is randomly
*Aperiodic tasks have soft deadlines or no deadlines

*The scheduling problem for aperiodic tasks is very different from the scheduling problem for
periodic tasks.
*Scheduling algorithms for aperiodic tasks must be able to guarantee the
deadlines for hard deadline aperiodic tasks and provide good average response times for
soft deadline aperiodic tasks even though the occurrence of the aperiodic requests are nondeterministic.

*Deadline remains as the important triggering factor for aperiodic tasks..

Release time-Aperiodic task

*Release time - It is the time at which the process becomes ready to execute. For aperiodic,the process is initiated by an event.
*The release time for aperiodic is measured from that event onwards.

c.

Sporadic Tasks in the Application
*Sporadic Tasks are similar to aperiodic tasks
*They repeat at random instances.
*The only difference is that sporadic tasks have hard deadlines.
*execution time of the task.
*minimum separation between the occurrence of two consecutive instances of the task.
*relative deadline of the task.

Release Time

One of its jobs Ji,c is released at t0
*A job in every higher-priority periodic task is released at t0
* The budget of the server is eS at t0, one or more aperiodic jobs are released at t0, and they
keep the server backlogged hereafter
*The next replenishment time of the server is t0 + eS