Publication 1756-UM523F-EN-P - December 2006
122
Maintain and Troubleshoot the System
Make All Your Tasks Periodic
Action
Details
1. If you have more than one task, make
them all periodic tasks.
If the controller contains only a periodic task or tasks, the system overhead time slice value
has no effect. Unscheduled communication happens whenever a periodic task is not
running.
Example
Suppose your task takes 50 ms to execute and you configure its period to 80 ms. In that
case, the controller has 30 ms out of every 80 ms for unscheduled communication.
2. Follow these guidelines to set the
periods of the tasks.
If you have multiple tasks, make sure that:
•
The execution time of a highest priority task is significantly less than its period.
•
The total execution time of all your tasks is significantly less than the period of the
lowest priority tasks.
This generally leaves enough time for unscheduled communication.
For example, in this configuration of tasks:
•
The execution time of the highest priority task (Task 1) is significantly less than its
period (20 ms is less than 80 ms).
•
The total execution time of all tasks is significantly less than the period of the lowest
priority task (50 ms is less than 100 ms).
3. Tune the periods of the tasks.
Adjust the periods of the tasks as needed to get the best trade-off between executing your
logic and servicing unscheduled communication.
4. Look for overlaps.
Look at the Monitor tab of the properties of the task to see if overlaps are happening. An
overlap happens if the period of a task is less than its scan time. If you see overlaps,
increase the period of the task.
50 ms
50 ms
50 ms
Periodic Task
30 ms
30 ms
30 ms
Unscheduled
Communication
Task
Priority
Execution Time
Rate
1
Higher
20 ms
80 ms
2
Lower
30 ms
100 ms
Total execution time:
50 ms
Содержание 1756-CNB/E
Страница 4: ...Publication 1756 UM523F EN P December 2006 Summary of Changes 4 Notes...
Страница 10: ...Publication 1756 UM523F EN P December 2006 10 Table of Contents...
Страница 26: ...Publication 1756 UM523F EN P December 2006 26 ControlLogix Redundancy System Overview Notes...
Страница 42: ...Publication 1756 UM523F EN P December 2006 42 Design the System Notes...
Страница 64: ...Publication 1756 UM523F EN P December 2006 64 Configure the System Redundancy Module Notes...
Страница 102: ...Publication 1756 UM523F EN P December 2006 102 Configure and Program the Controller Notes...
Страница 146: ...Publication 1756 UM523F EN P December 2006 146 Update Modules and Redundant Systems Notes...
Страница 162: ...Publication 1756 UM523F EN P December 2006 162 Set Up EtherNet IP Communication Across Subnets Notes...
Страница 168: ...Publication 1756 UM523F EN P December 2006 168 Convert an Existing System to Redundancy Notes...
Страница 178: ...Publication 1756 UM523F EN P December 2006 178 Redundant System Restrictions Notes...
Страница 185: ......