Integrate EasyEmbedded framework to Pi Pico project

Introduction

This project demonstrates how to integrate EasyEmbedded framework and FreeRTOS into a Pi Pico software project. The demonstrated project can be configured to run two applications:

• Two FreeRTOS tasks printing messages on the terminal
• Using task worker, which is an implementation of task queue/dispatch thread pattern.

Getting started

Getting the external library

All of the external libraries (Pico SDK, FreeRTOS, EasyEmbedded framework) are configured as submodules and they locate in lib folder. Executing the following commands to download the libraries.

cd lib

git submodule init

git submodule update

Configure the external library

Originally, after downloading the libraries, users should configure the libraries according to the target system. However, this reporitory includes already the configurations, so we just need to go through them and explain what each configuration does.

The starting point of the configuration is the CMakeLists.txt in the root folder.

Pico SDK

According to the Pico SDK, to integrate the it into a Pi Pico own project, the following steps must be done:

• Set the path PICO_SDK_PATH
• Include the cmake build script (pico_sdk_import.cmake)
• Set the standard output (we will use USB comport as debug output)
• Link the sdk to the targets

Those steps are translated to the following CMake commands:

set(PICO_SDK_PATH ${CMAKE_SOURCE_DIR}/lib/pico-sdk)

include(${PICO_SDK_PATH}/external/pico_sdk_import.cmake)


pico_enable_stdio_usb(main 1)
pico_add_extra_outputs(main)

target_link_libraries(main
PUBLIC
    pico_stdlib
    easy_embedded_lib
    freertos_kernel
)

Note: The commands above are just a collection of commands, they do not reflect their order in the CMake file. Please consult the final CMake file for the final result.

FreeRTOS

To integrate FreeRTOS, things are slightly complex. According to FreeRTOS getting started, to integrate FreeRTOS, we need to do the following steps:

• Set the path to FreeRTOS source
• Set the heap configuration
• Set the target (FreeRTOS port), provided that the port is available for that target
• Set the path to FreeRTOS import script for that target (FreeRTOS_Kernel_import.cmake)
• Provide a FreeRTOSConfigs.h file and link it to the build system
• Add FreeRTOS source files as subdirectory
• Link Pico SDK to FreeRTOS because the porting uses code from the Pico SDK
• Link the FreeRTOS to the project.

Those steps are translated to the following CMake commands:

set(FREERTOS_KERNEL_PATH ${CMAKE_SOURCE_DIR}/lib/FreeRTOS-Kernel)

include(${FREERTOS_KERNEL_PATH}/portable/ThirdParty/GCC/RP2040/FreeRTOS_Kernel_import.cmake)

# Config FreeRTOS
add_subdirectory(lib/EasyEmbeddedFramework)
set(FREERTOS_HEAP "4" CACHE INTERNAL "")
set(FREERTOS_PORT "GCC_RP2040" CACHE INTERNAL "")
add_library(freertos_config INTERFACE)
target_include_directories(freertos_config SYSTEM
INTERFACE
    ${CMAKE_SOURCE_DIR}/configs
)
target_compile_definitions(freertos_config
INTERFACE
    projCOVERAGE_TEST=0
)
target_link_libraries(freertos_config
INTERFACE
    pico_stdlib
)
add_subdirectory(lib/FreeRTOS-Kernel)

target_link_libraries(main
PUBLIC
    pico_stdlib
    easy_embedded_lib
    freertos_kernel
)

Note: The commands above are just a collection of commands, they do not reflect their order in the CMake file. Please consult the final CMake file for the final result.

EasyEmbedded framework

Integrate EasyEmbedded framework is relatively simple since most of the code are hardware-independent. To integrate the framework, following steps are required:

• Provide an configuration file (features.cmake), which contains a list of activated component and link the configuration file to CMake build
• Add the source code as subdirectory
• Link the framework to the project

include(${CMAKE_SOURCE_DIR}/configs/features.cmake)
add_subdirectory(lib/EasyEmbeddedFramework)

target_link_libraries(main
PUBLIC
    pico_stdlib
    easy_embedded_lib
    freertos_kernel
)

Note: The commands above are just a collection of commands, they do not reflect their order in the CMake file. Please consult the final CMake file for the final result.

If EasyEmbedded framework uses task worker, it also requires FreeRTOS. As long as FreeRTOS is configured as describe in the aboved section, things should be fine. The rest is taken care internally.

Caveat

If you build this project according to the steps in previous section, you will encounter the error: "error: 'sio_hw' undeclared (first use in this function)".

This error is caused by the following line:

sio_hw->fifo_wr = 0;

in the file FreeRTOS-Kernel/portable/ThirdParty/GCC/RP2040/port.c. This line is only needed when we use multicore. Therefore, we can comment this line out.

Build and run application

Building the application is straight forward, you just need to follow these steps (assume you are in the root folder):

mkdir build

cd build

cmake ..

cmake --build .

To flash the binary into the Pi Pico, please follow the Pi Pico Getting Started.

That's it. You have finished integrating several external libraries into your Pi Pico Project. Happy Coding!

Reference

• Pico SDK
• FreeRTOS Kernel
• EasyEmbedded framework