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freertos: Fix vTaskSuspendAll() and xTaskResumeAll()

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This commit fixes vTaskSuspendAll() and xTaskResumeAll() in the following ways.

- For vTaskSuspendAll()
    - Sync function source code with upstream single core version
    - Clearly mark IDF additions
- For xTaskResumeAll()
    - Sync function source code with upstream single core version
    - Clearly mark IDF additions
    - Fix bug where cores other than core 0 were allowed to unwind pended ticks
This commit is contained in:
Darian Leung
2022-07-11 17:00:47 +08:00
parent 5971253971
commit db26ff2503
2 changed files with 70 additions and 58 deletions
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14
docs/en/api-guides/freertos-smp.rst
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@@ -296,13 +296,17 @@ Vanilla FreeRTOS allows the scheduler to be suspended/resumed by calling :cpp:fu
On scheduler resumption, :cpp:func:`xTaskResumeAll` will catch up all of the lost ticks and unblock any timed out tasks.
In ESP-IDF FreeRTOS, suspending the scheduler across multiple cores is not possible. Therefore when :cpp:func:`vTaskSuspendAll` is called:
In ESP-IDF FreeRTOS, suspending the scheduler across multiple cores is not possible. Therefore when :cpp:func:`vTaskSuspendAll` is called on a particular core (e.g., core A):
- Task switching is disabled only on the current core but interrupts for the current core are left enabled
- Calling any blocking/yielding function on the current core is forbidden. Time slicing is disabled on the current core.
- If suspending on CPU0, the tick count is frozen. The tick interrupt will still occur to execute the application tick hook.
- Task switching is disabled only on core A but interrupts for core A are left enabled
- Calling any blocking/yielding function on core A is forbidden. Time slicing is disabled on core A.
- If an interrupt on core A unblocks any tasks, those tasks will go into core A's own pending ready task list
- If core A is CPU0, the tick count is frozen and a pended tick count is incremented instead. However, the tick interrupt will still occur in order to execute the application tick hook.
When resuming the scheduler on CPU0, :cpp:func:`xTaskResumeAll` will catch up all of the lost ticks and unblock any timed out tasks.
When :cpp:func:`xTaskResumeAll` is called on a particular core (e.g., core A):
- Any tasks added to core A's pending ready task list will be resumed
- If core A is CPU0, the pended tick count is unwound to catch up the lost ticks.
.. warning::
Given that scheduler suspension on ESP-IDF FreeRTOS will only suspend scheduling on a particular core, scheduler suspension is **NOT** a valid method ensuring mutual exclusion between tasks when accessing shared data. Users should use proper locking primitives such as mutexes or spinlocks if they require mutual exclusion.