Skip to main content

Freewheeling IEC Task

A freewheeling task is executed cyclically but without a fixed task cycle. This is a recurring task in the classic sense of the PLC.

Execution takes place as often as possible. However, processing does not take place in a fixed cycle. You cannot define a task cycle time for this kind of task. The time behavior is selected automatically and done in such a way that as little load as possible is placed on the overall system.

Moreover, a specific amount of time is waited after the end of a run until the task is executed again. The duration is a percentage of the last cycle duration.

Important

No fixed task cycle time and no fixed time behavior is guaranteed for the freewheeling task.

You can configure a watchdog for a freewheeling task.

Logic

The load of all freewheeling IEC tasks is determined by the runtime system so that this load does not exceed half of the set maximum processor load.

MaxCpuLoadFreewheeling = ((MIN( 100, MaxProcessorload) / 2) / NumOfFreeWheelingTasks);
SleeptimeAfterCycle = CycleTimeFreewheelingTask * ((100 - MaxCpuLoadFreewheeling) / 100)
if (SleeptimeAfterCycle < 1000) // Minimum sleeptime of 1ms is mandatory!   
SleeptimeAfterCycle = 1000;
Example 26. Example

The runtime system of an application runs as follows:

  • MaxProcessorload = 80

  • CycleTime = 20 ms

  • 1 freewheeling task

Effect

  • MaxCpuLoadFreewheeling = 40 %

  • SleeptimeAfterCycle = 30 ms

  • Total cycle time of the freewheeling task = 50 ms

⇒ A total CPU load of 60% is achieved for the rest of the system.



: