45 lines
1.8 KiB
ReStructuredText
45 lines
1.8 KiB
ReStructuredText
.. _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 still under construction, the API is not yet stable.
|
|
|
|
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.
|
|
|
|
SystemTimer backend
|
|
-------------------
|
|
The FreeRTOS based ``system_timer`` backend implements the
|
|
``pw_chrono:system_timer`` facade by using FreeRTOS's Software Timers API.
|
|
``pw::chrono::SystemTimer`` instances use ``StaticTimer_t`` &
|
|
``xTimerCreateStatic``, dynamic memory allocation is never used. This means
|
|
that both ``#define configUSE_TIMERS 1`` and
|
|
``#define configSUPPORT_STATIC_ALLOCATION 1`` must be set in the FreeRTOS
|
|
configuration.
|
|
|
|
This also means that FreeRTOS's ``Timer Service Daemon Task`` is used and must
|
|
be configured appropriately by the user through ``configTIMER_TASK_PRIORITY``,
|
|
``configTIMER_QUEUE_LENGTH``, and ``configTIMER_TASK_STACK_DEPTH``.
|
|
|
|
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``.
|