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FreeRTOS Scheduling question

Posted by e12 on July 27, 2016

I have question about freertos scheduling I’m using iar compiler and stm32f427 scheduling method is preemptive, I‘m using the hal library

Current Task are defined as follows:


As shown in Figure SDCARDWRITETask is run every 80ms using vTaskDelayUntil :


As shown in Figure ISS2OFPRunTask is run every 4ms using vTaskDelayUntil and semaphore give to OFP2CLAWRunTask run every 8ms, OFP2CLAWRunTask semaphore give to CLAWRunTask, CLAWRunTask semaphore give to CLAW2OFPRunTask :


**My question this if SDCARDWRITETask execution time 200ms, Is there any impact to other task ? **

is there any problem with scheduling?

FreeRTOS Scheduling question

Posted by rtel on July 27, 2016

The question "is there any problem with scheduling?" is not clear, but given the following description, you should be able to determine how your tasks will be scheduled. Further you can visualise the scheduling pattern using the FreeRTOS+Trace tool (http://www.freertos.org/trace).

If you are using pre-emptive scheduling (as you say you are) then the task selected to run by the FreeRTOS scheduler will always be the highest priority task that is able to run. A task is able to run if it:

  • is not in the Blocked state waiting for an event (message to arrive on a queue, direct to task notification, etc.) or a timeout.
  • is not in the Suspended state.

If there are more than one tasks at the highest priority that is able to run, then the task that has been waiting to run the longest will be selected. Then, if configUSE_TIMESLICING is set to 1 (or just not defined, in which case it will default to 1), tasks or equal priority will be selected in turn on each tick interrupt.......but as soon as a higher priority task because able to run the scheduler will switch to that higher priority task.

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