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The Scons arduino tool arduino.py is loosely based upon the earlier work of github user tomjnixon and his arduino-scons-alt repository. In August 2015, I found his work which hadn't been updated since 2013 and which (1) only ever worked for AVRs, (2) had never been updated to Arduino app versions later than 1.0, and (3) didn't prevent scons from leaving object files in the Arduino application directory tree.

arduino.py has been tested with Arduino 1.5 and 1.6 for both AVR and SAM/ARM architectures. To prevent object files from being left in the Arduino application's directory tree, a sleazy symlink trick is used owing to the restrictive behavior of scons' Repository() facility.

1. VariantDir() requires that the source files live in or below the main source tree. So, to use just VariantDir() the Arduino library sources need to be copied into the source tree so as to provide visibility to a scons build.

2. Repository() makes sources outside the source tree visible for building without leaving object files in that outside source tree. But, when combined with VariantDir() requires identical directory naming between the "mounted" repository and the VariantDir() directory. Consider, for example,

   source directory = src/
   build variant directory = BUILD/UNO/
   Arduino source directory = /usr/local/arduino/hardware/arduino/avr/
   

   With the commands

   VariantDir('BUILD/UNO', 'src')
   Repository('/usr/local/arduino/hardware/arduino/avr')
   

   there is now a problem. When scons looks for Arduino library sources to build, it will require them to be under

   /usr/local/arduino/hardware/arduino/avr/BUILD/UNO/
   

   This can be dealt with by making a symbolic link loop from UNO/ to avr/ but that may cause problems with unsuspecting programs. Alternatively, we can

   ln -s /usr/local/arduino/hardware/arduino \
         /usr/local/arduino/hardware/BUILD \
   ln -s /usr/local/arduino/hardware/arduino/avr \
         /usr/local/arduino/hardware/arduino/UNO \
   

   Thus, when told to build cores/arduino/*.cpp (core library) or libraries/SPI/*.cpp (SPI library), scons will find them under BUILD/UNO/cores/arduino and BUILD/UNO/libraries/SPI.

   This tool uses this latter symbolic link approach. It's admittedly sleazy -- it puts sym links into the Arduino tree -- but there's presently no better alternatives. The links are automatically established; you do not need to manually create them. This method can be used with

   • No VariantDir(),
   • VariantDir('a', ), and
   • VariantDir('a/b', )

   That is, this code works with no variant directory, a single-directory level variant directory, and a two-directory level variant directory.

Copy the arduino.py file to your project. It can be kept tucked away in a subdirectory. Scons also has methods for installing it in site-wide or per-user scons "tool" directories. The examples provided here keep it in a subdirectory named scons_tools and provide that directory's name and location with the Environment() call.

In you SConstruct file, set into os.environment()

1. The Arduino application version as an single integer (e.g., for 1.5.8beta, use "158"; for 1.6.5, use "165").

    os.environ['ARDUINO_VERSION'] = '158'
   

2. The path to the directory containing the Arduino application's hardware folder,

    os.environ['ARDUINO_HOME'] = '/usr/local/arduino'
   

   Note this is not the path for the hardware folder itself: it is the path to the folder containing the hardware folder.

3. For ARM/SAM architectures and Ardiuno 1.6 or later, the path to the directory tree in which the separately installed gcc toolchain is located. E.g.,

    os.environ['ARDUINO_TOOLS'] = '/Users/dnewman/Library/Arduino15/packages/arduino/tools/arm-none-eabi-gcc/4.8.3-2014q1'
   

See the example SConstruct files for working examples of effecting the above three settings.

When creating the scons environment, declare usage of the tool arduino and the location of the directory containing arduino.py. For example,

env = Environment(tools = ['default', 'arduino'],
                  toolpath = ['scons_tools'] )

To then load information about the target Arduino board, issue the command

env.ConfigureBoard(arduino_version, arduino_arch, board, options)

where

1. arduino_version is an actual integer (not a string) representing the Arduino version number (e.g., 158, 165, etc.).

2. arduino_arch is the string 'avr' or 'sam' and represents the target architecture. Yes, this could be derived from board but that would require either maintaining a table or making guesses in order to find the correct boards.txt file. (The location of boards.txt is dependent on both the target architecture and the version of the Arduino application.)

3. board is the Arduino board name as it appears in the architecture's boards.txt (e.g., "uno", "arduino_due_x").

4. options is used to control how the Arduino platform.txt compile recipes are transformed into CC and C++ commands for use with scons. The Arduino recipes have undesirable (dubious) settings such as -w which disables all compiler warnings. These options may be used to drop (strip) or replace portions of the recipes

   options is a dictionary containing any or all of the following keys

   • cc_flags_drop_list -- strings to drop from CC commands
   • cc_flags_replace_list -- strings to replace in CC commands
   • cxx_flags_drop_list -- strings to drop from C++ (CXX) commands
   • cxx_flags_replace_list -- strings to replace in C++ (CXX) commands

   A replace list is a list of 2-tuples, each 2-tuple containing two strings: a substring to look for and a substring to replace it with. E.g., to replace -w with -Wall and -Os with -O2, use

   [ ('-w', '-Wall'), ('-Os', '-O2') ] 
   

   Note that depending upon a replace list may cause problems after upgrading the Arduino application: a new Arduino platform.txt file may no longer specify a given switch. With the above example, if you need -O2 specified but -Os is no longer used in the new platform.txt, then the replacement will not occur and thus -O2 will not be asserted. It is safer to strip unwanted flags/switches with a drop list and use env.Append() to add assert necessary flags or switches for CCFLAGS or CXXFLAGS.

   A drop list is a list of 2-tuples, each 2-tuple containing a string to drop and a count of the subsequent number of tokens following the string to also drop. E.g., the drop list

   [ ('-o', 1) ]
   

   drops the -o switch and the single argument immediately following it. The following drops both -o and -w,

   [ ('-o', 1), ('-w', 0) ]
   

Two complete examples are provided. After editing their SConstruct files to have Arduino version and path information specific to your computer, they should build with a simple scons command.

• example_simple/ is a simple Arduino program which requires the Arduino core and SoftwareSerial libraries. It builds in situ rather than to a variant directory.

• example_variant/ builds to a variant directory, build/<board-name>/. In addition to using Arduino libraries, it also provides a library of its own in src/libraries/. Note that library sources do not need to be in a subdirectory. And if placed in a subdirectory, then the name is arbitrary. Libraries do not need to be in a subdirectory named libraries.