/**
   * @defgroup    sys_arduino Arduino
   * @ingroup     sys
   * @brief       Arduino in RIOT
   *
   * @section sec_about About
   *
   * This module enables users to run unmodified Arduino sketches in RIOT. For
   * this we aim at supporting the full Arduino API.
   *
   * The support of the Arduino API in RIOT is useful for multiple reasons:
   * - starting point for beginners
   * - run your existing sketches on any non-Arduino hardware supported by RIOT
   * - makes it easy to move from Arduino to RIOT
   * - use Arduino device drivers in RIOT
   * - is fun to implement :-)
   *
   * Refer to @ref sys_arduino_api for the actual API documentation
   *
   *
   * @section sec_usage General usage
   *
   * To run your Arduino sketch in RIOT, just follow these steps:
   *
   * -# create an empty application
   * -# add the `arduino` module to your application, your `Makefile` should now
   *    look something like this:
   * @code
   * APPLICATION = YOUR_APP_NAME
   * BOARD ?= YOUR_TARGET_PLATFORM
   * RIOTBASE ?= PATH_TO_RIOT_ROOT
   *
   * USEMODULE += arduino
   *
   * include $(RIOTBASE)/Makefile.include
   * @endcode
   *
   * -# copy your Arduino sktech(es) into your application folder. Currently they
   *    must have the file ending `*.sketch` to be processed.
   * -# build, flash, and run your application the usual RIOT-way: simply call
   *    `make all`, `make flash`, `make term`, etc.
   *
   * Thats all. As bonus you can of course use any existing RIOT code inside your
   * Arduino sketches - you simply have to add the includes to your sketch and
   * the corresponding modules to your `Makefile`.
   *
   * @note  So far, all Arduino sketches MUST have the file ending `*.sketch` to
   *        be recognized by RIOT's build system
   *
   *
   * @section sec_concept Concept
   *
   * For enabling RIOT to run Arduino sketches, we extended the build system to
   * handle `*.sketch` files and we implemented the Arduino API using RIOT's
   * native functions.
   *
   * @subsection sec_concept_build Extension of the build system
   *
   * Building Arduino sketches in RIOT is done in a two step process.
   *
   * First, the make system calls a dedicated
   * [Arduino build script](https://github.com/RIOT-OS/RIOT/tree/master/dist/tools/arduino/pre_build.sh),
   * which is called from the
   * [Makefile.include](https://github.com/RIOT-OS/RIOT/tree/master/sys/arduino/Makefile.include)
   * of the RIOT Arduino module.
   *
   * This script creates a temporary file called '_sketches.cpp' inside the
   * application folder. Into this file, the script copies some Arduino glue code (
   * [pre.snip](https://github.com/RIOT-OS/RIOT/blob/master/sys/arduino/pre.snip)
   *  and
   * [post.snip](https://github.com/RIOT-OS/RIOT/blob/master/sys/arduino/post.snip))
   * together with the contents of all `*.sketch` files contained in the
   * application folder.
   *
   * Second, the RIOT make system is called as usual, processing the temporary
   * file containing all the Arduino code. Simple :-)
   *
   * @subsection sec_conecpt_api Implementation of the Arduino API
   *
   * For supporting the Arduino API, we have created our own function and class
   * definitions, using the exact same signatures as in the original Arduino
   * header files. These headers are then implemented using standard RIOT APIs,
   * e.g. the peripheral drivers, `xtimer`, etc.
   *
   *
   * @section sec_boardsupport Add Arduino support to a board
   *
   * @note As prerequisite, the board must have support for C++.
   *
   * To add Arduino support to a board, it has to provide the following:
   *
   * In `RIOT/board/BOARD/include/arduino_board.h`:
   * - a mapping of GPIO pins to Arduino pin numbers named `arduino_pinmap`, e.g.
   * @code{c}
   *  static const gpio_t arduino_pinmap[] = {
   *      GPIO_PIN(PORT_D, 12),
   *      GPIO_PIN(PORT_D, 13),
   *      GPIO_PIN(PORT_D, 14),
   *      GPIO_PIN(PORT_D, 15),
   *      GPIO_PIN(PORT_A, 12),
   *      GPIO_PIN(PORT_A, 15),
   *      GPIO_PIN(PORT_B, 1),
   *      GPIO_PIN(PORT_B, 2),
   *      ...
   *  };
   * @endcode
   *
   * - a define `ARDUINO_LED` that is mapped to an Arduino pin number connected to
   *   any on-board LED, or to pin 0 in case no LED is defined:
   * @code{c}
   *  #define ARDUINO_LED         (2)
   * @endcode
   *   This links to the third entry in the `arduino_pinmap` array.
   *
   * In addition, you have to add the 'arduino' feature to the board. For this,
   * just add `FEATURES_PROVIDED += arduino` to the 'other features' section in
   * your board's `Makefile.features'.
   *
   * That's it, your board can now run Ardunio sketches.
   *
   *
   * @section sec_todo Open issues
   *
   * @todo Make it possible to bootstrap Arduino code manually from any RIOT
   *       application. Include a pseudomule as e.g. arduino_base, which does not
   *       implement a main function calling `setup()` and `loop()`, so these
   *       functions have to be called manually from a RIOT application.
   * @todo Implement analog outputs (PWM mapping)
   * @todo Implement analog inputs (ADC mapping)
   * @todo Implement SPI interface class
   * @todo Add support for the 'Wire Library' (I2C)
   * @todo Add means to include various Arduino Libraries (maybe as pkg?)
   * @todo Implement anything else that is missing...
   * @todo Adapt Arduino build script, so sketches do not have to have the file
   *       ending `*.sketch` anymore
   */