Temporal Control
Time-Triggered Systems
The execution of an activity (function) is triggered via a control signal based on the progression of time (e.g., through a periodic timer interrupt).
Systems are triggered by the progression of time.
Typical e.g. in control applications of cyber-physical systems.
There is a common time reference (allows establishing phase relations).
CPU utilization is constant, even when there are no changes in the system state.
The worst case situation is well-defined.
Event-Triggered Systems
The execution of activities (functions) is triggered through an asynchronous control signal based on a change of system state (e.g., through an external interrupt).
Systems are controlled by the occurrence of events in the environment.
Typical of sporadic conditions monitoring the system state (e.g., alarm verification or asynchronous requests).
The utilization rate of the computing system resources (e.g. CPU) is variable, depending on the frequency of occurrence of events.
Ill-defined worst case situation. Implies either:
use of probability arguments, or
imposition of limitations on the maximum rate of events.
Example
For the following task sets compute the maximum response time that each task may experiment:
Compute the average and maximum CPU utilization rate for both cases.
Admit that, on average, ET tasks are activated every 100 time units.
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