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2e99832616
Move to use :option:`CONFIG_XYZ` vs :option:`XYZ` to generate propert links and avoid warnings about unexistant targets. Change-Id: I4b46041f25e538462b123ccc8337f733033cc0e7 Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
79 lines
2.3 KiB
ReStructuredText
79 lines
2.3 KiB
ReStructuredText
.. _nanokernel_tasks:
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Task Services
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#############
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Concepts
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********
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A :dfn:`task` is a preemptible thread of execution that implements a portion of
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an application's processing. It is normally used to perform processing that is
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too lengthy or too complex to be performed by a fiber or an ISR.
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A nanokernel application can define a single application task, known as the
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*background task*, which can execute only when no fiber or ISR needs to
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execute. The entry point function for the background task is :code:`main()`,
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and it must be supplied by the application.
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.. note::
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The background task is very different from the tasks used by a microkernel
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application; for more information see :ref:`microkernel_tasks`.
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Task Lifecycle
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==============
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The kernel automatically starts the background task during system
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initialization.
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Once the background task is started, it executes forever. If the task attempts
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to terminate by returning from :code:`main()`, the kernel puts the task into
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a permanent idling state since the background task must always be available
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to execute.
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Task Scheduling
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===============
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The nanokernel's scheduler executes the background task only when no fiber or
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ISR needs to execute; fiber and ISR executions always take precedence.
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The kernel automatically saves the background task's CPU register values when
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prompted for a context switch to a fiber or ISR. These values are restored
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when the background task later resumes execution.
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Usage
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*****
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Defining the Background Task
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============================
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The application must supply a function of the following form:
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.. code-block:: c
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void main(void)
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{
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/* background task processing */
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...
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/* (optional) enter permanent idling state */
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return;
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}
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This function is used as the background task's entry point function. If a
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nanokernel application does not need to perform any task-level processing,
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:code:`main()` can simply do an immediate return.
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The :option:`CONFIG_MAIN_STACK_SIZE` configuration option specifies
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the size, in bytes, of the memory region used for the background
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task's stack and for other execution context information.
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APIs
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****
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The nanokernel provides the following API for manipulating the background task.
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:cpp:func:`task_sleep()`
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Put the background task to sleep for a specified time period.
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