FreeRTOS

The $dir_pw_third_party/freertos/ module contains various helpers to use FreeRTOS, including Pigweed backend modules which depend on FreeRTOS.

Build Support

This module provides support to compile FreeRTOS with GN and CMake. This is required when compiling backends modules for FreeRTOS.

GN

In order to use this you are expected to configure the following variables from $dir_pw_third_party/freertos:freertos.gni:

  1. Set the GN dir_pw_third_party_freertos to the path of the FreeRTOS installation.

  2. Set pw_third_party_freertos_CONFIG to a pw_source_set which provides the FreeRTOS config header.

  3. Set pw_third_party_freertos_PORT to a pw_source_set which provides the FreeRTOS port specific includes and sources.

After this is done a pw_source_set for the FreeRTOS library is created at $dir_pw_third_party/freertos.

CMake

In order to use this you are expected to set the following variables from third_party/freertos/CMakeLists.txt:

  1. Set dir_pw_third_party_freertos to the path of the FreeRTOS installation.

  2. Set pw_third_party_freertos_CONFIG to a library target which provides the FreeRTOS config header.

  3. Set pw_third_party_freertos_PORT to a library target which provides the FreeRTOS port specific includes and sources.

Linking against FreeRTOS kernel’s static internals

In order to link against internal kernel data structures through the use of extern “C”, statics can be optionally disabled for the tasks.c source file to enable use of things like pw_thread_freertos/util.h’s ForEachThread.

To facilitate this, Pigweed offers an opt-in option which can be enabled by configuring GN through pw_third_party_freertos_DISABLE_TASKS_STATICS = true or CMake through set(pw_third_party_freertos_DISABLE_TASKS_STATICS ON CACHE BOOL "" FORCE). This redefines static to nothing for the Source/tasks.c FreeRTOS source file when building through $dir_pw_third_party/freertos in GN and through pw_third_party.freertos in CMake.

Attention

If you use this, make sure that your FreeRTOSConfig.h and port does not rely on any statics inside of tasks.c. For example, you cannot use PW_CHECK for configASSERT when this is enabled.

As a helper PW_THIRD_PARTY_FREERTOS_NO_STATICS=1 is defined when statics are disabled to help manage conditional configuration.

We highly recommend our configASSERT wrapper when using this configuration, which correctly sets configASSERT to use PW_CHECK` and ``PW_ASSERT for you.

OS Abstraction Layers Support

Support for Pigweed’s OS Abstraction Layers are provided for FreeRTOS via the following modules:

configASSERT and pw_assert

To make it easier to use pw_assert with FreeRTOS a helper header is provided under pw_third_party/freertos/config_assert.h which defines configASSERT for you using Pigweed’s assert system for your FreeRTOSConfig.h if you chose to use it.

// Instead of defining configASSERT, simply include this header in its place.
#include "pw_third_party/freertos/config_assert.h"