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32 lines
1.2 KiB
32 lines
1.2 KiB
.. _module-pw_chrono_freertos:
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------------------
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pw_chrono_freertos
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------------------
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``pw_chrono_freertos`` is a collection of ``pw_chrono`` backends that are
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implemented using FreeRTOS.
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.. warning::
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This module is under construction, not ready for use, and the documentation
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is incomplete.
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SystemClock backend
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-------------------
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The FreeRTOS based ``system_clock`` backend implements the
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``pw_chrono:system_clock`` facade by using ``xTaskGetTickCountFromISR()`` and
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``xTaskGetTickCount()`` based on the current context. An InterruptSpinLock is
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used to manage overflows in a thread and interrupt safe manner to produce a
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signed 64 bit timestamp.
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The ``SystemClock::now()`` must be used more than once per overflow of the
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native FreeRTOS ``xTaskGetTickCount*()`` overflow. Note that this duration may
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vary if ``portSUPPRESS_TICKS_AND_SLEEP()``, ``vTaskStepTick()``, and/or
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``xTaskCatchUpTicks()`` are used.
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Build targets
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-------------
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The GN build for ``pw_chrono_freertos`` has one target: ``system_clock``.
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The ``system_clock`` target provides the
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``pw_chrono_backend/system_clock_config.h`` and ``pw_chrono_freertos/config.h``
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headers and the backend for the ``pw_chrono:system_clock``.
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