Prerequisite – Tasks in Real Time systems
1. Periodic Real-time Tasks :
The real-time task that is repeated after a certain time interval is known as periodic real-time task. Basically the periodic real-time tasks are controlled by the clock interrupts. Therefore, the periodic real-time tasks are also called clock-driven tasks.
For example, in a chemical plant temperatures, pressure and other attribute are measured periodically and all information is passed to controller.
2. Sporadic Real-time Tasks :
The real-time task that reoccurs at random instant is known as sporadic real-time task. Sporadic real-time task has some similarity to aperiodic real-time task but it is different from aperiodic real-time task. Basically all the high critical tasks are sporadic tasks.
For example, fire handling task in industry is sporadic task.
Difference between Periodic and Sporadic Real-time Tasks :
|PERIODIC TASK||SPORADIC TASK|
|It reoccurs after a certain period of time.||It reoccurs at random instant.|
|It is controlled by clock interrupts.||It is not controlled by clock interrupts.|
|Time of occurrence of periodic tasks can be predicted.||Time of occurrence of sporadic tasks can’t be predicted.|
|It includes moderate critical or low critical tasks.||It includes highly critical tasks.|
|It includes normal system tasks.||It includes tasks that may lead to system failure.|
|It can be easily scheduled by cyclic scheduler.||It is complex to schedule sporadic tasks by cyclic scheduler.|
|Periodic tasks are allotted time frame in generalized task scheduler.||Sporadic tasks are allotted slack time in generalized task scheduler.|
|Example: Measuring of temperature and pressure at a time interval.||Example: Emergency message arrivals in the system.|
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