Creating a New EMAC OE SDK Project with CMake

The EMAC OE SDK is distributed with the intent that CMake be used with the EMAC OE toolchain and libraries to build most projects. This page demonstrates the process of creating and compiling a new project with CMake, and running it on the target machine.

General Information

Creating a new EMAC CMake project is accomplished with the use of the oe_init_project program. This program is included in the emac-tools-projects apt package, which is part of the EMAC SDK. For instructions on installing the EMAC SDK, please see this section in the getting started guide.

Creating a New EMAC OE SDK Project with CMake

This section demonstrates how to use the EMAC CMake tool, oe_init_project, to generate CMake files automatically for a project. When using the EMAC SDK there are currently two options for cross compiling:

arm
x86

For the purposes of this guide, the arm option will be used for the listed examples.

Host Machine Compiling

Navigate to the directory where the project will be located. Then run the CMake new project tool, oe_init_project.

developer@ldc:~/projects#  oe_init_project -n hello.c 
If desired, please enter a name for this project, otherwise press Enter to use the default: hello_emac 

-- Creating new project directory... 

-- Creating new source file... 

-- Building custom CMakeLists.txt file... 

-- Done. 

Do you want to create a build directory for this project? (y/n) y 

-- Creating build directory... 

Do you want to run cmake for this project? (y/n) y 

-- Using system compiler 

-- The C compiler identification is GNU 4.8.2 

-- The CXX compiler identification is GNU 4.8.2 

-- Check for working C compiler: /usr/bin/cc 

-- Check for working C compiler: /usr/bin/cc -- works 

-- Detecting C compiler ABI info 

-- Detecting C compiler ABI info - done 

-- Check for working CXX compiler: /usr/bin/c++ 

-- Check for working CXX compiler: /usr/bin/c++ -- works 

-- Detecting CXX compiler ABI info 

-- Detecting CXX compiler ABI info - done 

-- Configuring done 

-- Generating done 

-- Build files have been written to: /home/developer/projects/hello_emac/hello_emac-build 

Do you want to compile this project? (y/n) y
Scanning dependencies of target hello_emac 

[100%] Building C object CMakeFiles/hello_emac.dir/hello.c.o 

Linking C executable hello_emac 

[100%] Built target hello_emac

The executable, in this case, is now inside the hello_emac/hello_emac-build directory.

Target Machine Compiling

The CMake project script has now made a project directory that contains the following:

CMakeLists.txt
Source code file (hello.c in this case)
README file
Desktop Build Directory (hello_emac-build in this case)

Despite what the file extension implies, the CMakeLists.txt is actually a script which contains the required information to automatically create a Makefile for any supported architecture. This file was generated by the EMAC oe_init_project tool, and will need to be modified over time as a project grows. The comments in the CMakeLists.txt file generated by the EMAC tool will provide a good starting point for how to add additional source files and how to perform other common tasks related to maintaining your CMake build system as you develop your software project. The CMake project provides extensive documentation on how to work with these files.

The source code file generated by the script (hello.c) contains a basic Hello World style program. This can provide a starting point for your application, or be replaced by another source file with the same name.

The README file contains more information on using CMake with the EMAC OE 5.0 SDK. You may refer to this file for quick reference.

The Desktop Build Directory (hello_emac-build) contains the executable, hello_emac, the Makefile, and various cache files. These were automatically created by CMake and by the build system, and can be recreated at any time.

It is useful to have a Desktop Build Directory because it is easier (in the beginning) to use the desktop to verify all code changes before cross-compiling for a target board. This will be useful until the application under development depends upon resources which are only available on the target hardware, such as certain device drivers or the touchscreen (if so equipped).

Use the following steps to cross-compile the project and send it to a target board.

In a terminal, navigate to the base directory of the project.

NOTE
If the architecture of the target board you're using for your appliction x86, then you will need to change all occurrences of arm in the following sections below to x86.
Create a build directory for cross compiling.

developer@ldc:~/projects/hello_emac# mkdir hello_emac-build-arm
Navigate into the newly created directory.

developer@ldc:~/projects/hello_emac# cd hello_emac-build-arm
Run cmake using the target architecture.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# cmake .. -DARCH:STRING=arm
Compile the code using make.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# make

The make command creates the target executable in the hello_emac-build-arm directory.
Now copy the executable to the target board. For information on copying the executable file, see the Transferring Files section.

Examples

This section will illustrate how to complete various different tasks associated with building a CMake project.

Debug Build Types

By default, new projects will have the Debug build type. To compile the project with the Release or Minimum Size Release build types, there are two options:

Make a secondary (or tertiary) build directory. (Recommended)
Clean the current build directory and re-run CMake.

WARNING!

We should really have a table showing the types of releases targets available, along with a description. So, here's an example:

Name:	Type:	Debugging Features:	Description	Pre-Processor Defines
Release	Release	disabled	Release targeted build optimized for speed.	RELEASE_BUILD (???)
MinSizeRel	Release	disabled	Release targeted build optimized for small size.	RELEASE_BUILD (???)
Debug	Debug	enabled	A standard debugging oriented build, optimized for speed with -O2 (this is a guess)	__DEBUG__ (???)
etc.

WARNING!

This is really useful information for any developer. Knowing the level of optimization is insightful, so that should be included. Knowing whether or not the build was stripped of debugging information is important if they ever intend to release binaries to the public (such as for updates) and to ensure small size and max speed. Knowing what preprocessor defines are #def'd with a target is really useful when writing debugging code.

I would put all this in a table like the example I made above (but accurate and complete). The border-radius and shadows will need to be overridden to make it look right. Can always use css or a template for this.

Method 1

To create a Release build using the 1st (recommended) method, use the following steps:

In a terminal, navigate to the base directory of the project.
Create a new release build directory

developer@ldc:~/projects/hello_emac# mkdir hello_emac-build-arm-release
Change directories into the newly created directory.

developer@ldc:~/projects/hello_emac# cd hello_emac-build-arm-release
Run cmake using the target architecture.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# cmake .. -DARCH:STRING=arm -DCMAKE_BUILD_TYPE:STRING=Release

NOTE
The string 'MinSizeRel' can be used in place of 'Release' for a potentially smaller executable
Compile the code using make.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# make

Method 2

Another option for creating a release build is as follows:

In a terminal, navigate to the build directory of the project.
Clean the directory with make

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# make clean
Run cmake using the target architecture.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# cmake .. -DARCH:STRING=arm -DCMAKE_BUILD_TYPE:STRING=Release

NOTE
The string 'MinSizeRel' can be used in place of 'Release' for a potentially smaller executable
Compile the code using make.

developer@ldc:~/projects/hello_emac/hello_emac-build-arm# make

WARNING!

What's the difference between these two build options? One seems to just be a way to change build options and recompile, although you're using the exact same options for configuring CMake. How's the 2nd one different, and why is the 1st one recommended over the 2nd one?

Adding Include Files

To add an include file (in this case, the tools.cpp and tools.h in the include directory) to the cmake project, changes will need to be made to the CMakeLists.txt file. Please refer to the code sample below.

The directory to be included must be specified by the INCLUDE_DIRECTORIES() function. The variable ${PROJECT_SOURCE_DIR} refers to the base path of the project which is generally where this README file is located.
The SOURCES must be set. This list of files should include all of the source files in the project.

INCLUDE_DIRECTORIES(${PROJECT_SOURCE_DIR}/include)

SET(SOURCES
     ${PROJECT_SOURCE_DIR}/main.cpp
     ${PROJECT_SOURCE_DIR}/include/tools.cpp
     ${PROJECT_SOURCE_DIR}/include/tools.h
     )

WARNING!

Implementation files don't belong in include/ directories. People usually put them in src/ directories, the project root directory, or a directory named for the functionality (such as tools/).

Renaming the Target Executable

To rename the executable, the ADD_EXECUTABLE() function arguments must be changed. The first argument refers to the name of the executable, and the second refers to the source code file.

To change the name of the executable from "main" to "new_name", change the ADD_EXECUTABLE() from the first code box to the second code box.

ADD_EXECUTABLE(main main.cpp)

ADD_EXECUTABLE(new_name main.cpp)

WARNING!

Don't you need to add tools.cpp to this list as well, if you added that to your project?

Creating a New EMAC OE SDK Project with CMake

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General Information