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Diffstat (limited to 'pw_chrono_freertos/docs.rst')
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diff --git a/pw_chrono_freertos/docs.rst b/pw_chrono_freertos/docs.rst new file mode 100644 index 000000000..cb0d31818 --- /dev/null +++ b/pw_chrono_freertos/docs.rst @@ -0,0 +1,31 @@ +.. _module-pw_chrono_freertos: + +------------------ +pw_chrono_freertos +------------------ +``pw_chrono_freertos`` is a collection of ``pw_chrono`` backends that are +implemented using FreeRTOS. + +.. warning:: + This module is under construction, not ready for use, and the documentation + is incomplete. + +SystemClock backend +------------------- +The FreeRTOS based ``system_clock`` backend implements the +``pw_chrono:system_clock`` facade by using ``xTaskGetTickCountFromISR()`` and +``xTaskGetTickCount()`` based on the current context. An InterruptSpinLock is +used to manage overflows in a thread and interrupt safe manner to produce a +signed 64 bit timestamp. + +The ``SystemClock::now()`` must be used more than once per overflow of the +native FreeRTOS ``xTaskGetTickCount*()`` overflow. Note that this duration may +vary if ``portSUPPRESS_TICKS_AND_SLEEP()``, ``vTaskStepTick()``, and/or +``xTaskCatchUpTicks()`` are used. + +Build targets +------------- +The GN build for ``pw_chrono_freertos`` has one target: ``system_clock``. +The ``system_clock`` target provides the +``pw_chrono_backend/system_clock_config.h`` and ``pw_chrono_freertos/config.h`` +headers and the backend for the ``pw_chrono:system_clock``. |