C++ Example using CMake

In some situations, developers intend to implement software using the NuttX platform in a previously set hardware and configuration where it is not possible or allowed to make changes. In such situations, less contact with the operating source tree is better, where it is only used for the application.

Some approaches are possible to do that today:

We have been seen the increase of the use of C++ language in embedded systems application. And CMake (https://www.cmake.org) is the preferred build system used to build C++ projects. NuttX support C++ based projects.

Using the ‘build as a library’ procedure of NuttX, it is possible to build NuttX applications using C++ language and also the cmake build tool.

This document will show how to reimplement the hellocpp project using this cmake.

Preparation

  1. Base NuttX compilation changes

    For this example, load the configuration ‘stm32f4discovery:testlibcxx’ for building

    $ cd nuttx
    $ ./tools/configure.sh stm32f4discovery:testlibcxx
    

    In menuconfig, the main points to be changed on a typical NuttX configuration are the following:

    • Set RTOS Features -> Tasks and Scheduling -> Application entry point to ‘hellocpp_main’

    • Build NuttX and generate the export

    $ make export
    

Creating the project

  1. Create your project file structure

    The project structure is organized as follow:

    hellocpp/
    hellocpp/CMakeLists.txt
    hellocpp/cmake/stm32f4discovery.cmake
    hellocpp/nuttx-export-10.0.1/
    hellocpp/src/CMakeLists.txt
    hellocpp/src/main.cpp
    hellocpp/src/HelloWorld.h
    hellocpp/src/HelloWorld.cpp
    

    The directory ‘nuttx-export-10.0.1’ is the unzipped content from the file created during make export procedure done before.

  2. File contents

  • hellocpp/CMakeLists.txt

cmake_minimum_required(VERSION 3.2...3.15)

project(HelloCpp
        VERSION 1.0
        DESCRIPTION "Hello world C++ Nuttx"
)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
# set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_C_STANDARD 99)

set(NUTTX_PATH "${CMAKE_SOURCE_DIR}/nuttx-export-10.0.1")

include(cmake/stm32f4discovery.cmake)

set(AC_COMMON_FLAGS "${AC_COMMON_FLAGS} -fno-builtin -Wall -Wshadow -Wundef -fno-strict-aliasing -fno-strength-reduce -fomit-frame-pointer -Os")
set(AC_COMMON_FLAGS "${AC_COMMON_FLAGS} -D_DEBUG -D_LIBCPP_BUILD_STATIC -D_LIBCPP_NO_EXCEPTIONS ")
set(AC_COMMON_FLAGS "${AC_COMMON_FLAGS} -fno-exceptions -fcheck-new -fno-rtti -pedantic ")
set(AC_COMMON_FLAGS "${AC_COMMON_FLAGS} -nostdinc++")

set(AC_DEFINES "${AC_DEFINES} -DCONFIG_WCHAR_BUILTIN")

include_directories(
        src
        ${NUTTX_PATH}/include
        ${NUTTX_PATH}/include/libcxx
        ${NUTTX_PATH}/arch/chip
)

set(EXE_NAME hellocpp)

set(CMAKE_CXX_FLAGS     "${AC_HW_FLAGS} ${AC_DEFINES} ${AC_COMMON_FLAGS} ${AC_CXX_EXTRA_FLAGS}")
if (PARAM_DEBUG)
    set(CMAKE_CXX_FLAGS     "${CMAKE_CXX_FLAGS} -g")
endif()

set(CMAKE_SKIP_RPATH ON)
set(CMAKE_CXX_LINK_EXECUTABLE "${CMAKE_LINKER} ${AC_LINKER_FLAGS} -o ${EXE_NAME}.elf <OBJECTS> <LINK_LIBRARIES>")

set(BUILD_SHARED_LIBS OFF)

add_subdirectory(src)
  • hellocpp/cmake/stm32f4discovery.cmake

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(MCU_LINKER_SCRIPT "${NUTTX_PATH}/scripts/ld.script")

set(COMPILER_PREFIX arm-none-eabi-)

# cmake-format: off
set(CMAKE_C_COMPILER    ${COMPILER_PREFIX}gcc)
set(CMAKE_CXX_COMPILER  ${COMPILER_PREFIX}g++)
set(CMAKE_AR            ${COMPILER_PREFIX}ar)
set(CMAKE_RANLIB        ${COMPILER_PREFIX}ranlib)
set(CMAKE_LINKER        ${COMPILER_PREFIX}ld)
set(CMAKE_ASM_COMPILER  ${COMPILER_PREFIX}gcc)
set(CMAKE_OBJCOPY       ${COMPILER_PREFIX}objcopy)
set(CMAKE_OBJDUMP       ${COMPILER_PREFIX}objdump)
set(CMAKE_SIZE          ${COMPILER_PREFIX}size)

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)

set(AC_HW_FLAGS         "-mcpu=cortex-m4 -mthumb -mfloat-abi=soft ")
set(AC_HW_FLAGS         "${AC_HW_FLAGS} -isystem ${NUTTX_PATH}/include")
set(AC_HW_FLAGS         "${AC_HW_FLAGS} -pipe -D__NuttX__")

set(AC_LINKER_FLAGS     "--entry=__start -nostartfiles -nodefaultlibs -T${MCU_LINKER_SCRIPT}")
  • hellocpp/src/CMakeLists.txt

set(HEADER_FILES
        HelloWorld.h
)

set(SOURCE_FILES
        HelloWorld.cpp
)

link_directories(${EXE_NAME} ${NUTTX_PATH}/libs)

add_executable(${EXE_NAME} ${SOURCE_FILES} main.cpp ${HEADER_FILES})

add_custom_command(
        TARGET ${EXE_NAME}
        POST_BUILD
        COMMAND ${CMAKE_OBJCOPY} ARGS -S -O binary ${CMAKE_BINARY_DIR}/${EXE_NAME}.elf ${CMAKE_BINARY_DIR}/${EXE_NAME}.bin
)

target_link_libraries(${EXE_NAME} --start-group)

target_link_libraries(${EXE_NAME} sched)
target_link_libraries(${EXE_NAME} drivers)
target_link_libraries(${EXE_NAME} boards)
target_link_libraries(${EXE_NAME} c)
target_link_libraries(${EXE_NAME} mm)
target_link_libraries(${EXE_NAME} arch)
target_link_libraries(${EXE_NAME} xx)
target_link_libraries(${EXE_NAME} apps)
target_link_libraries(${EXE_NAME} fs)
target_link_libraries(${EXE_NAME} binfmt)
target_link_libraries(${EXE_NAME} board)
target_link_libraries(${EXE_NAME} gcc)
target_link_libraries(${EXE_NAME} supc++)

target_link_libraries(${EXE_NAME} --end-group)
  • hellocpp/src/main.cpp

#include "HelloWorld.h"
#include <nuttx/config.h>

extern "C"
{
        int hellocpp_main(void)
        {

                CHelloWorld *pHelloWorld = new CHelloWorld();
                pHelloWorld->HelloWorld();

                CHelloWorld helloWorld;
                helloWorld.HelloWorld();

                delete pHelloWorld;
                return 0;
        }
}
  • hellocpp/src/HelloWorld.h

#ifndef HELLOWORLD_H_
#define HELLOWORLD_H_

#include "nuttx/config.h"

class CHelloWorld
{
        public:
                CHelloWorld();
                ~CHelloWorld();
                bool HelloWorld(void);
        private:
                int mSecret;
};

#endif
  • hellocpp/src/HelloWorld.cpp

#include <cstdio>
#include <string>

#include "HelloWorld.h"

CHelloWorld::CHelloWorld() {
        mSecret = 42;
        std::printf("Constructor: mSecret=%d\n",mSecret);
}

CHelloWorld::~CHelloWorld() {

}

bool CHelloWorld::HelloWorld(void) {
        std::printf("HelloWorld: mSecret=%d\n",mSecret);

        std::string sentence = "Hello";
        std::printf("TEST=%s\n",sentence.c_str());

        if (mSecret == 42) {
                std::printf("CHelloWorld: HelloWorld: Hello, world!\n");
                return true;
        }
        else {
                std::printf("CHelloWorld: HelloWorld: CONSTRUCTION FAILED!\n");
                return false;
        }
}

Building

To launch build, you use the cmake procedure:

$ mkdir build
$ cd build
$ cmake ..
$ make

And finally a bin file will be created to be loaded on the board.