AP Bridge SConstruct details

This section describes additional details of the SCons build script used to compile the AP Bridge software. You may need to further modify the SConstruct file if you install the toolchain or other dependencies in a different location than described in the build instructions. 

TODO: update SCons snippets and provide where paths should be set (instead of where it is used)

Certain parts of the build scripts may need to be adjusted to specify the location of files on the host build platform. The SConstruct file defines a build environment that contains the path to the compiler(s) and the search paths for headers and libraries. 

The SConstruct is organized to allow for targets to be built for different platforms based on the target option to the scons command. SCons uses the Environment data structure to set build parameters such as the compiler path, header search directories, libraries to link against, etc.  

The getHOSTEnv function configures common parameters for a particular build host. This function should be used to set common tools, compile flags and directory paths, such as the path to the directory where the required libraries are installed. The SCons documentation lists the built-in variables that are used to construct the compilation commands. 

def getLinuxEnv(baseEnv):
    boost_incdir, boost_libdir = findBoostDirs(baseEnv)
    env = baseEnv.Clone(
        HOST_ARCH = platform.machine() + '-linux',
        TOOLS_DIR = baseEnv['tools_prefix'],  # tools_prefix can be passed as a command option
        BOOST_BASE= baseEnv['boost_prefix'],  # boost_prefix can be passed as a command option
        ...
        CPPPATH=[
            '#',
            '$TOOLS_DIR/include',
            boost_incdir,
        ],
        # Linker flags
        LIBPATH=[
            '$TOOLS_DIR/lib',
            boost_libdir,
        ],
    )
    # Compile actions for various intermediate languages
    env['PROTOC'] = '/usr/local/bin/protoc'
    ...
    return env

The get_TARGET_platform function specializes the configuration for a particular target platform. This may involve changing the compiler path and updating the compiler flags. The RPi 2 platform function contains several target-specific names that may need to be updated if you use a different cross-compiler. 

def get_raspi2_platform(env):
    'Set architecture-specific flags for raspberry pi 2'
    # compiler location
    env['CXX']  = '$toolchain_dir/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-g++'
    env['LINK'] = '$toolchain_dir/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-g++'
    ...
    # other variables are defined in this function to customize the build process for this target
    env['PLATFORM'] = 'armpi-linux'

Manually overriding SConstruct variables

Certain variables, such as target can be specified on the scons command line. For example, to use a toolchain installed in /tools/armpi-linux/arm-bcm2708:

$ scons toolchain_dir=/tools/armpi-linux/arm-bcm2708 apbridge

By default, scons prints a help message containing a list of all the variables and their default values. Some variables are used internally as part of the Dust build and release process. 

$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
default(["default"], [])

To build the AP Bridge software:

 $ scons apbridge                      # build the AP Bridge for i386
 $ scons apbridge target=armpi         # build the AP Bridge for Raspberry Pi

 $ scons apbridge_pkg                  # Create AP Bridge package for i386
 $ scons apbridge_pkg target=armpi     # Create AP Bridge package for Raspbery Pi

For internal use, to build an AP Bridge release:

 $ scons apbridge_release

Options for building:

debug: Build with debug symbols
    default: True
    actual: True

opt: Build with optimization
    default: False
    actual: False
...