Chapter 4. API Guides
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1. Starting state. None of the ready state tasks have been selected to run
Head [ AX , B0 , C1 , D0 ] Tail
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2. Core 0 has tick interrupt and searches for a task to run.
Task A is selected and is moved to the back of the list
Core0--|
Head [ AX , B0 , C1 , D0 ] Tail
0
Head [ B0 , C1 , D0 , AX ] Tail
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3. Core 1 has a tick interrupt and searches for a task to run.
Task B cannot be run due to incompatible affinity, so core 1 skips to Task C.
Task C is selected and is moved to the back of the list
Core1-------| 0
Head [ B0 , C1 , D0 , AX ] Tail
0 1
Head [ B0 , D0 , AX , C1 ] Tail
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4. Core 0 has another tick interrupt and searches for a task to run.
Task B is selected and moved to the back of the list
Core0--| 1
Head [ B0 , D0 , AX , C1 ] Tail
1 0
Head [ D0 , AX , C1 , B0 ] Tail
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5. Core 1 has another tick and searches for a task to run.
Task D cannot be run due to incompatible affinity, so core 1 skips to Task A
Task A is selected and moved to the back of the list
Core1-------| 0
Head [ D0 , AX , C1 , B0 ] Tail
0 1
Head [ D0 , C1 , B0 , AX ] Tail
The implications to users regarding the Best Effort Round Robin time slicing:
• Users cannot expect multiple ready state tasks of the same priority to run sequentially (as is the case in Vanilla
FreeRTOS). As demonstrated in the example above, a core may need to skip over tasks.
• However, given enough ticks, a task will eventually be given some processing time.
• If a core cannot find a task runnable task at the highest ready state priority, it will drop to a lower priority to
search for tasks.
• To achieve ideal round robin time slicing, users should ensure that all tasks of a particular priority are pinned
to the same core.
Espressif Systems 1362
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