Modeling Example "Purely Periodic without Communication"

This system architecture pattern consists of a task set, where each task is activated periodically and no data accesses are performed. The execution time for each task is determined by the called runnable entities as specified in the table below. All tasks contain just one runnable except of T7, which calls at first R7,1 and after that R7,2.

The table below gives a detailed specification of the tasks and their parameters. The tasks are scheduled according fixed-priority, preemptive scheduling and if not indicated otherwise, all events are active in order to get a detailed insight into the system’s behavior.

Task Priority Preemption Multiple Task Activation Limit Activation Execution Time
T1 7 FULL 1 Periodic R1 Uniform
Offset = 0 Min = 9.95
Recurrence = 80 Max = 10
T2 6 FULL 1 Periodic R2 Uniform
Offset = 0 Min = 29.95
Recurrence = 120 Max = 30
T3 5 FULL 1 Periodic R3 Uniform
Offset = 0 Min = 19.95
Recurrence = 160 Max = 20
T4 4 FULL 1 Periodic R4 Uniform
Offset = 0 Min = 14.95
Recurrence = 180 Max = 15
T5 3 FULL 1 Periodic R5 Uniform
Offset = 0 Min = 29.95
Recurrence = 200 Max = 30
T6 2 FULL 1 Periodic R6 Uniform
Offset = 0 Min = 39.95
Recurrence = 300 Max = 40
T7 1 FULL 1 R7,1 Uniform
Min = 59.95
Periodic Max = 60
Offset = 0 R7,2 Uniform
Recurrence = 1000 Min = 19.95
Max = 20

In order to show the impact of changes to the model, the following consecutive variations are made to the model:

1) Initial Task Set
For this variation, the Tasks T4, T5, T6, and T7 of the table above are active.
2) Increase of Task Set Size I
For this variation, the Tasks T3, T4, T5, T6, and T7 are active. That way the utilization of the system is increased.
3) Increase of Task Set Size II
For this variation, the Tasks T1, T3, T4, T5, T6, and T7 are active. That way the utilization of the system is increased.
4) Increase of Task Set Size III
As from this variation on, all tasks (T1 - T7) are active. That way the utilization of the system is increased.
5) Accuracy in Logging
For this variation, just task events are active. That way, only a limited insight into the system’s runtime behavior is available.
6) Schedule
As from this variation on, T7 is set to non-preemptive. That way, the timing behavior is changed, which results in extinct activations (see red mark in the figure below).
7) Activation
As from this variation on, the maximum number of queued activation requests for all tasks is set to 2. That way, the problem with extinct activations resulting from the previous variation is solved.
8) Schedule Point
For this variation, a schedule point is added to T7 between the calls of R7,1 and R7,2. That way, the timing behavior is changed in particular.
9) Scheduling Algorithm
For this variation, the scheduling algorithm is set to Earliest Deadline First. That way, the timing behavior is changed completely.