Building FreeRTOS with Eclipse
Using relative paths to reference the RTOS source code

Introduction

The FreeRTOS download contains many different pre-configured demo application projects, but for maintenance and sanity reasons it contains only one copy of the RTOS source code. Ideally each demo project would reference and build the single RTOS source code copy, and this is exactly what most of the pre-configured RTOS demo projects do. However, historically this has not been easy (although not impossible) to do in Eclipse, and older Eclipse based RTOS demo projects use a batch file to copy all the necessary source files from their default locations in the FreeRTOS directory tree into the Eclipse project directory.

The latest versions of Eclipse have gone some way to alleviate these problems by allowing the definition of variables that can resolve paths both up and down the directory tree from the directory that contains the Eclipse .project file. Newer RTOS demo applications that are built with an Eclipse based IDEs are pre-configured to use this improved (although still comparatively awkward) method, instead of the batch file method used previously. This page describes how these projects are created.

Note: This page is provided for information only. The RTOS demo projects in the official FreeRTOS download are already pre-configured, and should build 'out of the box', provided the build instructions specific to the demo project in use are followed, and that the Eclipse version in use is up to date.


Creating Eclipse Projects that Build Files Outside of the Project Directory

By way of example the following instructions show how to reference the FreeRTOS source files, which reside in the /FreeRTOS/Source directory, from an Eclipse project file, which resides in the /FreeRTOS/Demo/[project_name] directory.


  1. Open the Project's Properties Window

    Right click on the project's name in the Eclipse Project Explorer window, then select 'Properties' from the pop up menu. The Properties window will open.


  2. Define a New Eclipse Variable

    In the Properties window, select 'Resources->Linked Resources' to view the path variables. Click the 'New' button to create a new variable that will be used to point to the FreeRTOS source files directory tree.

    Defining a new Eclipse variable that will be used to reference the RTOS source files
    Define a new Eclipse variable


    Name the new variable FREERTOS_ROOT, and use the pre-defined PROJECT_LOC variable to enter a path that resolves to the /FreeRTOS/Source directory.

    Use a relative path to set the Eclipse variable to the RTOS source directory
    Extending the PROJECT_LOC variable so it resolves to the /FreeRTOS/Source directory


    Close the Properties window.


  3. Creating a Virtual Folder

    Eclipse managed make projects build all the source files that appear in the Project Explorer window. The RTOS source files are outside of the Eclipse project directory, so don't automatically appear in the Project Explorer window, and must be added manually using a virtual folder.

    Right click on the folder name in the Project Explorer under which you would like the RTOS source files to appear. Select 'New -> Folder'. The New Folder window will open.

    In the New Folder window, enter FreeRTOS as the folder name, and select the 'Folder is not located in the file system (Virtual Folder)' radio button.

    Create a virtual folder in Eclipse Project Explorer
    Creating a virtual folder in the Eclipse Project Explorer


  4. Linking the RTOS Source Code Directory Into The Virtual Folder

    Right click on the newly created virtual folder and select 'New -> Folder' from the pop up menu to bring up the New Folder window again.

    Creating a linked resource in Eclipse
    Right click the virtual folder in order to view the pop up menu

    In the new folder window, enter Source as the directory name, and this time select the 'Link to alternative location (Linked Folder)' radio button. Enter the newly created FREERTOS_ROOT variable as the folder's location.

    Using a relative path to add files into an Eclipse project
    Using a relative path to add a linked folder into an Eclipse project


  5. Selecting the Files To Build

    The FreeRTOS/Source directory is now visible within the Eclipse Project explorer. The directory contains the source files for every RTOS port, so the next step is to use Eclipse resource filters to ensure only the files necessary to build the FreeRTOS port actually being used are visible.

    Right click on the Portable directory to view the pop up menu again, this time select 'Properties'. A pop up window that shows the proprieties of the Portable directory will be displayed.

    View the properties of the RTOS source code directory
    Viewing the properties of the RTOS Source code's Portable directory


    In the Properties window, select 'Resources->Resource Filters' to view the directory's resource filters. Create two 'Include Only' resource filters so the only directories that are shown match the text 'MemMang' and '[compiler]', where [compiler] is the compiler used to build the source files. By way of example, the next two images show the settings to use if the project is being built with the Renesas compiler.

    Adding Eclipse resource filters to down select the RTOS source files being built
    Defining 'Include Only' resource filters on the directories


    The Eclipse project resource filters
    The Resource Filters window after the two filters have been defined.


    At the time of writing, the MemMang directory contains four .c files, each of which provides one of four different options for heap memory management. Add a resource filter to the MemMang directory to ensure only one of the four .c files is visible.

    Ensure only one RTOS heap source file is built
    Using a resource filter to ensure only one heap_x.c file is built, heap_4.c in the depicted case


    The [compiler] directory will contain a sub directory for each architecture FreeRTOS supports with that compiler. Add a resource filter to the [compiler] directory to ensure only the directory for the architecture actually being used is visible. For example, the resource filter being created in the image below is correct if the Renesas compiler is being used to build a project that targets a microcontroller form the RX600 family.

    Ensuring only the source files for the architecture the RTOS is being built for are shown
    Creating a resource filter to ensure only one sub directory under the [compiler] directory is visible


  6. Adding Linked Directories Into the Compiler's Include Path

    Virtual and linked folders can be added to the compiler's include path in the normal way.

    Adding the RTOS's header source files to the project's include path
    Adding directories from the virtual and linked folders into the compiler's include path






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