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freertos: Update FreeRTOS overview document
This commit updates "freertos.rst" to act as an overview document of FreeRTOS in ESP-IDF, outlining the different FreeRTOS implementations (IDF vs Amazon) and various supplemental features. The details of each implementation will be separated to their own documents.
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| FreeRTOS | ||
| ======== | ||
| FreeRTOS (Overview) | ||
| =================== | ||
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| Overview | ||
| -------- | ||
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| This section contains documentation of FreeRTOS types, functions, and macros. It is automatically generated from FreeRTOS header files. | ||
| FreeRTOS is an open source real-time operating system kernel that acts as the operating system for ESP-IDF applications and is integrated into ESP-IDF as a component. The FreeRTOS component in ESP-IDF contains ports of the FreeRTOS kernel for all the CPU architectures used by ESP targets (i.e., Xtensa and RISC-V). Furthermore, ESP-IDF provides different implementations of FreeRTOS in order to support SMP (Symmetric Multiprocessing) on multi-core ESP targets. This document provides an overview of the FreeRTOS component, the FreeRTOS implementations offered by ESP-IDF, and the common aspects across all implementations. | ||
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| .. note:: | ||
| ESP-IDF FreeRTOS is based on Vanilla FreeRTOS v10.4.3 | ||
| Implementations | ||
| --------------- | ||
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| - For more information about the SMP changes of ESP-IDF FreeRTOS, see :doc:`/api-guides/freertos-smp` | ||
| - For more information about the features added to ESP-IDF FreeRTOS, see :doc:`/api-reference/system/freertos_additions`. | ||
| The `official FreeRTOS <https://www.freertos.org/index.html>`_ (henceforth referred to as Vanilla FreeRTOS) is a single-core RTOS. In order to support the various multi-core ESP targets, ESP-IDF supports different FreeRTOS implementations, namely **ESP-IDF FreeRTOS** and **Amazon SMP FreeRTOS**. | ||
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| Configuration | ||
| ------------- | ||
| ESP-IDF FreeRTOS | ||
| ^^^^^^^^^^^^^^^^ | ||
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| Vanilla FreeRTOS allows ports and applications to configure the kernel by adding various ``#define config...`` macros to ``FreeRTOSConfig.h``. Through these macros, the kernel's scheduling behavior and various kernel features can be enabled or disabled. **However, in ESP-IDF FreeRTOS, the ``FreeRTOSConfig.h`` file is considered a private and must not be modified by users**. Any FreeRTOS configuration that is exposed to the user will be done so via menuconfig. | ||
| ESP-IDF FreeRTOS is a FreeRTOS implementation based on Vanilla FreeRTOS v10.4.3, but contains significant modifications to support SMP. ESP-IDF FreeRTOS only supports two cores at most (i.e., dual core SMP), but is more optimized for this scenario by design. For more details regarding ESP-IDF FreeRTOS and its modifications, please refer to the :doc:`freertos_idf` document. | ||
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| ESP-IDF FreeRTOS can be configured in the project configuration menu (``idf.py menuconfig``) under ``Component Config/FreeRTOS``. The following section highlights some of the ESP-IDF FreeRTOS configuration options. For a full list of ESP-IDF FreeRTOS configurations, see :doc:`/api-reference/kconfig` | ||
| .. note:: | ||
| ESP-IDF FreeRTOS is currently the default FreeRTOS implementation for ESP-IDF. | ||
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| - :ref:`CONFIG_FREERTOS_UNICORE` will run ESP-IDF FreeRTOS only on CPU0. Note that this is **not equivalent to running Vanilla FreeRTOS**. Furthermore, this option may affect behavior of components other than :component:`freertos`. For more details regarding the effects of running ESP-IDF FreeRTOS on a single core, refer to :ref:`freertos-smp-single-core`. Alternatively, users can also search for occurrences of ``CONFIG_FREERTOS_UNICORE`` in the ESP-IDF components. | ||
| Amazon SMP FreeRTOS | ||
| ^^^^^^^^^^^^^^^^^^^ | ||
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| - :ref:`CONFIG_FREERTOS_TASK_FUNCTION_WRAPPER` will enclose all task functions within a wrapper function. In the case that a task function mistakenly returns (i.e. does not call :cpp:func:`vTaskDelete`), the call flow will return to the wrapper function. The wrapper function will then log an error and abort the application, as illustrated below:: | ||
| Amazon SMP FreeRTOS is an SMP implementation of FreeRTOS that is officially supported by Amazon. Amazon SMP FreeRTOS is able to support N-cores (i.e., more than two cores). Amazon SMP FreeRTOS can be enabled via the :ref:`CONFIG_FREERTOS_SMP` option. For more details regarding Amazon SMP FreeRTOS, please refer to the `official Amazon SMP FreeRTOS documentation <https://freertos.org/symmetric-multiprocessing-introduction.html>`_. | ||
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| E (25) FreeRTOS: FreeRTOS task should not return. Aborting now! | ||
| abort() was called at PC 0x40085c53 on core 0 | ||
| .. warning:: | ||
| The Amazon SMP FreeRTOS implementation (and its port in ESP-IDF) are currently in experimental/beta state. Therefore, significant behavioral changes and breaking API changes can occur. | ||
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| .. only:: CONFIG_FREERTOS_UNICORE | ||
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| .. note:: | ||
| As {IDF_TARGET_NAME} is a single core SoC, the :ref:`CONFIG_FREERTOS_UNICORE` configuration is always set. | ||
| Configuration | ||
| ------------- | ||
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| Kernel Configuration | ||
| ^^^^^^^^^^^^^^^^^^^^ | ||
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| .. _freertos-applications: | ||
| Vanilla FreeRTOS requires that ports and applications configure the kernel by adding various ``#define config...`` macros to ``FreeRTOSConfig.h``. Vanilla FreeRTOS supports a list of kernel configuration options which allow various kernel behaviors and features to be enabled or disabled. | ||
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| ESP-IDF FreeRTOS Applications | ||
| ----------------------------- | ||
| **However, for all FreeRTOS ports in ESP-IDF, the ``FreeRTOSConfig.h`` file is considered private and must not be modified by users**. A large number of kernel configuration options in ``FreeRTOSConfig.h`` are hard coded as they are either required or not supported in ESP-IDF. All kernel configuration options that are configurable by the user will be exposed via menuconfig under ``Component Config/FreeRTOS/Kernel``. | ||
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| Unlike Vanilla FreeRTOS, users must not call :cpp:func:`vTaskStartScheduler`. Instead, ESP-IDF FreeRTOS is started automatically. The entry point is a user defined ``void app_main(void)`` function. | ||
| For the full list of user configurable kernel options, see :doc:`/api-reference/kconfig`. The list below highlights some commonly used kernel configuration options: | ||
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| - Typically, users would spawn the rest of their applications task from ``app_main``. | ||
| - The ``app_main`` function is allowed to return at any point (i.e., before the application terminates). | ||
| - The ``app_main`` function is called from the ``main`` task. | ||
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| The ``main`` task is one of multiple tasks that are automatically spawned by ESP-IDF during startup. These tasks are: | ||
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| .. only:: not CONFIG_FREERTOS_UNICORE | ||
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| .. list-table:: List of Tasks Created During Startup | ||
| :widths: 25 25 5 50 | ||
| :header-rows: 1 | ||
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| * - Task Name | ||
| - Affinity | ||
| - Priority | ||
| - Description | ||
| * - Main Task (``main``) | ||
| - CPU0 | ||
| - 1 | ||
| - Task that simply calls ``app_main``. This task will self delete when ``app_main`` returns | ||
| * - Idle Tasks (``IDLEx``) | ||
| - CPU0 and CPU1 | ||
| - 0 | ||
| - Idle tasks created for (and pinned to) each CPU | ||
| * - IPC Tasks (``ipcx``) | ||
| - CPU0 and CPU1 | ||
| - 24 | ||
| - IPC tasks created for (and pinned to) each CPU. IPC tasks are used to implement the Inter-processor Call (IPC) feature. See :doc:`/api-reference/system/ipc` for more details. | ||
| - :ref:`CONFIG_FREERTOS_UNICORE` will run FreeRTOS only on CPU0. Note that this is **not equivalent to running Vanilla FreeRTOS**. Furthermore, this option may affect behavior of components other than :component:`freertos`. For more details regarding the effects of running FreeRTOS on a single core, refer to :ref:`freertos-smp-single-core` (if using ESP-IDF FreeRTOS) or the official Amazon SMP FreeRTOS documentation. Alternatively, users can also search for occurrences of ``CONFIG_FREERTOS_UNICORE`` in the ESP-IDF components. | ||
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| .. only:: CONFIG_FREERTOS_UNICORE | ||
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| .. list-table:: List of Tasks Created During Startup | ||
| :widths: 25 25 5 50 | ||
| :header-rows: 1 | ||
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| * - Task Name | ||
| - Affinity | ||
| - Priority | ||
| - Description | ||
| * - Main Task (``main``) | ||
| - CPU0 | ||
| - 1 | ||
| - Task that simply calls ``app_main``. This task will self delete when ``app_main`` returns | ||
| * - Idle Tasks (``IDLE``) | ||
| - CPU0 | ||
| - 0 | ||
| - Idle task created for CPU0 | ||
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| .. note:: | ||
| As {IDF_TARGET_NAME} is a single core SoC, the :ref:`CONFIG_FREERTOS_UNICORE` configuration is always set. | ||
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| Low priority numbers denote low priority tasks. | ||
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| Task API | ||
| -------- | ||
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| .. include-build-file:: inc/task.inc | ||
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| Queue API | ||
| --------- | ||
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| .. include-build-file:: inc/queue.inc | ||
| - :ref:`CONFIG_FREERTOS_ENABLE_BACKWARD_COMPATIBILITY` enables backward compatibility with some FreeRTOS macros/types/functions that were deprecated from v8.0 onwards. | ||
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| Semaphore API | ||
| ------------- | ||
| Port Configuration | ||
| ^^^^^^^^^^^^^^^^^^ | ||
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| .. include-build-file:: inc/semphr.inc | ||
| All other FreeRTOS related configuration options that are not part of the kernel configuration are exposed via menuconfig under ``Component Config/FreeRTOS/Port``. These options configure aspects such as: | ||
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| Timer API | ||
| --------- | ||
| - The FreeRTOS ports themselves (e.g., tick timer selection, ISR stack size) | ||
| - Additional features added to the FreeRTOS implementation or ports | ||
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| .. include-build-file:: inc/timers.inc | ||
| Using FreeRTOS | ||
| -------------- | ||
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| Event Group API | ||
| --------------- | ||
| Application Entry Point | ||
| ^^^^^^^^^^^^^^^^^^^^^^^ | ||
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| .. include-build-file:: inc/event_groups.inc | ||
| Unlike Vanilla FreeRTOS, users of FreeRTOS in ESP-IDF **must never call** :cpp:func:`vTaskStartScheduler` and :cpp:func:`vTaskEndScheduler`. Instead, ESP-IDF will start FreeRTOS automatically. Users must define a ``void app_main(void)`` function which acts as the entry point for user's application and is automatically called on ESP-IDF startup. | ||
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| Stream Buffer API | ||
| ----------------- | ||
| - Typically, users would spawn the rest of their application's task from ``app_main``. | ||
| - The ``app_main`` function is allowed to return at any point (i.e., before the application terminates). | ||
| - The ``app_main`` function is called from the ``main`` task. | ||
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| Background Tasks | ||
| ^^^^^^^^^^^^^^^^ | ||
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| During startup, ESP-IDF and FreeRTOS will automatically create multiple tasks that run in the background (listed in the the table below). | ||
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| .. list-table:: List of Tasks Created During Startup | ||
| :widths: 10 75 5 5 5 | ||
| :header-rows: 1 | ||
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| * - Task Name | ||
| - Description | ||
| - Stack Size | ||
| - Affinity | ||
| - Priority | ||
| * - Idle Tasks (``IDLEx``) | ||
| - An idle task (``IDLEx``) is created for (and pinned to) each CPU, where ``x`` is the CPU's number. | ||
| - :ref:`CONFIG_FREERTOS_IDLE_TASK_STACKSIZE` | ||
| - CPUx | ||
| - ``0`` | ||
| * - FreeRTOS Timer Task (``Tmr Svc``) | ||
| - FreeRTOS will create the Timer Service/Daemon Task if any FreeRTOS Timer APIs are called by the application. | ||
| - :ref:`CONFIG_FREERTOS_TIMER_TASK_STACK_DEPTH` | ||
| - CPU0 | ||
| - :ref:`CONFIG_FREERTOS_TIMER_TASK_PRIORITY` | ||
| * - Main Task (``main``) | ||
| - Task that simply calls ``app_main``. This task will self delete when ``app_main`` returns | ||
| - :ref:`CONFIG_ESP_MAIN_TASK_STACK_SIZE` | ||
| - :ref:`CONFIG_ESP_MAIN_TASK_AFFINITY` | ||
| - ``1`` | ||
| * - IPC Tasks (``ipcx``) | ||
| - When :ref:`CONFIG_FREERTOS_UNICORE` is false, an IPC task (``ipcx``) is created for (and pinned to) each CPU. IPC tasks are used to implement the Inter-processor Call (IPC) feature. | ||
| - :ref:`CONFIG_ESP_IPC_TASK_STACK_SIZE` | ||
| - CPUx | ||
| - ``24`` | ||
| * - ESP Timer Task (``esp_timer``) | ||
| - ESP-IDF will create the ESP Timer Task used to process ESP Timer callbacks. | ||
| - :ref:`CONFIG_ESP_TIMER_TASK_STACK_SIZE` | ||
| - CPU0 | ||
| - ``22`` | ||
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| .. include-build-file:: inc/stream_buffer.inc | ||
| .. note:: | ||
| Note that if an application uses other ESP-IDF features (e.g., WiFi or Bluetooth), those features may create their own background tasks in addition to the tasks listed in the table above. | ||
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| Message Buffer API | ||
| FreeRTOS Additions | ||
| ------------------ | ||
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| .. include-build-file:: inc/message_buffer.inc | ||
| ESP-IDF provides some supplemental features to FreeRTOS such as Ring Buffers, ESP-IDF style Tick and Idle Hooks, and TLSP deletion callbacks. See :doc:`freertos_additions` for more details. |