/**
 * @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
 */