doc: develop: manifests: external: add arduino core

Add documentation for the Arduino Core API for zephyr which sits
as an external module as of today.

Signed-off-by: Dhruva Gole <d-gole@ti.com>

Author: DhruvaG2000

doc/develop/manifest/external/arduino-core-api.rst

@@ -0,0 +1,199 @@
+.. _external_module_arduino_core_api:
+
+Arduino Core API
+################
+
+Introduction
+************
+
+The Arduino-Core-Zephyr module started as a `Google Summer of Code 2022 project`_
+to provide Arduino-style APIs for Zephyr RTOS applications. This module acts as an abstraction
+layer, allowing developers familiar with Arduino programming to leverage Zephyr's capabilities
+without having to learn entirely new APIs and libraries.
+
+Understanding the Components
+============================
+
+This module consists of two key components that work together:
+
+**1. ArduinoCore-API (Common Arduino API Definition)**
+
+The `ArduinoCore-API <https://github.com/arduino/ArduinoCore-API>`_ is Arduino's official
+hardware abstraction layer that defines the common Arduino API. It contains the abstract API
+definitions **and** implementations for hardware-independent functionality.
+
+Key characteristics:
+
+* Contains both API definitions (headers) and hardware-agnostic implementations
+* Provides classes like ``String``, ``Print``, ``Stream``, ``IPAddress`` with full implementations
+* Defines interfaces for hardware-specific classes (e.g., ``HardwareSerial``, ``HardwareSPI``)
+* Shared across all modern Arduino platforms for consistency
+* See the `ArduinoCore-API README <https://github.com/arduino/ArduinoCore-API#arduinocore-api>`_ for implementation details
+* It is Licensed as GNU LESSER GENERAL PUBLIC LICENSE Version 2.1
+
+**2. Arduino-Core-Zephyr (Zephyr-Specific Implementation)**
+
+The `Arduino-Core-Zephyr <https://github.com/zephyrproject-rtos/arduino-core-zephyr>`_ module
+provides the **Zephyr-specific implementation** of the Arduino API. This is where hardware-dependent
+Arduino functions are implemented using Zephyr's native APIs and drivers.
+
+Key characteristics:
+
+* Contains the ``cores/arduino`` directory with Zephyr implementations (``zephyrCommon.cpp``, ``zephyrSerial.cpp``, etc.)
+* Provides board-specific variants with pin mappings and Device Tree overlays
+* Includes Zephyr build system integration (CMake, Kconfig, west.yml)
+* Links to ArduinoCore-API to inherit the common implementations
+* See the `project documentation <https://github.com/zephyrproject-rtos/arduino-core-zephyr/tree/main/documentation>`_ for implementation details
+* It is Licensed under Apache-2.0
+
+Features Provided
+=================
+
+Together, these components provide:
+
+* Standard Arduino API functions like ``pinMode()``, ``digitalWrite()``, ``analogRead()``, etc.
+* Support for Arduino-style ``setup()`` and ``loop()`` functions
+* Pin mapping between Arduino pin numbers and Zephyr's GPIO definitions
+* Support for common Arduino communication protocols (Serial, I2C, SPI)
+* Compatibility with existing Arduino libraries
+* Board variant support for various hardware platforms already present in Zephyr
+
+By bringing Arduino-style programming to Zephyr, this module provides a gentler learning curve
+for those transitioning from Arduino to Zephyr while still benefiting from Zephyr's advanced
+features, scalability, and broad hardware support.
+
+Usage with Zephyr
+*****************
+
+Adding the Arduino Core API to a Zephyr Project
+===============================================
+
+#. To pull in the Arduino Core for Zephyr as a Zephyr module, either add it as
+   a West project in the west.yaml file or pull it in by adding a submanifest
+   (e.g. ``zephyr/submanifests/arduino-core.yaml``) file with the following content
+   and run west update:
+
+   .. code-block:: yaml
+
+      # Arduino API repository
+      - name: Arduino-Core-Zephyr
+        path: modules/lib/arduinocore-zephyr
+        revision: main
+        url: https://github.com/zephyrproject-rtos/arduino-core-zephyr
+
+#. Run the following command to update your project:
+
+   .. code-block:: bash
+
+      west update
+
+#. For Linux users, there's an ``install.sh`` script in the module that will automatically
+   link the ArduinoCore-API. If you can't use this script, follow the manual steps below.
+
+   .. note::
+
+      Skip the next step if the install.sh script succeeded. The next step is for Linux
+      users who may have a difference in where the module is installed or have some custom
+      Zephyr setup with custom paths.
+
+#. Complete the core setup by linking the API folder from the ArduinoCore-API repository into
+   the arduinocore-zephyr folder:
+
+   .. code-block:: bash
+
+      git clone https://github.com/arduino/ArduinoCore-API # Any location
+      cd /<path>/<to>/<zephyrproject>/modules/lib/arduinocore-zephyr
+      ln -s /<your>/<location>/arduinocore-zephyr/api cores/arduino/.
+
+   The ``cores`` folder is located inside ``<zephyr-project-path>/modules/lib/arduinocore-zephyr/cores``.
+
+Using Arduino Core API in Your Application
+==========================================
+
+#. In your application's ``prj.conf`` file, enable the Arduino API configs similar to how it's being
+   done in the `blinky_arduino sample`_.
+
+#. Create your application using Arduino-style code:
+
+   .. code-block:: cpp
+
+      #include <Arduino.h>
+
+      void setup() {
+        pinMode(LED_BUILTIN, OUTPUT);
+      }
+
+      void loop() {
+        digitalWrite(LED_BUILTIN, HIGH);
+        delay(1000);
+        digitalWrite(LED_BUILTIN, LOW);
+        delay(1000);
+      }
+
+#. Build your application with the target board:
+
+   .. code-block:: bash
+
+      west build -b <board_name> path/to/your/app
+
+Supported Boards
+================
+
+The Arduino Core API module currently has variants for these boards:
+
+* :zephyr:board:`arduino_mkrzero`
+* :zephyr:board:`arduino_nano_33_ble` (including Sense variant)
+* :zephyr:board:`arduino_nano_33_iot`
+* :zephyr:board:`beagleconnect_freedom`
+* :zephyr:board:`cc3220sf_launchxl`
+* :zephyr:board:`nrf52840dk`
+* :zephyr:board:`rpi_pico`
+
+Adding Custom Board Support
+===========================
+
+To add support for a custom board:
+
+#. Create a new folder in the ``variants/`` directory with your board's name
+#. Add an overlay file and a pinmap header file that match the board name
+#. Add your new headerfile to an ``#ifdef`` statement in the ``variant.h`` file
+
+For detailed instructions on adding board variants, refer to the `board variants documentation`_.
+
+Using External Arduino Libraries
+================================
+
+To use external Arduino libraries with your Zephyr project:
+
+#. Add your library's source files (e.g., ``MyLibrary.h`` and ``MyLibrary.cpp``) to your project's ``src`` folder
+#. Update your application's ``CMakeLists.txt`` to include these files:
+
+   .. code-block:: cmake
+
+      target_sources(app PRIVATE src/MyLibrary.cpp)
+
+#. Include the library in your source code:
+
+   .. code-block:: cpp
+
+      #include "MyLibrary.h"
+
+For more details on using external libraries, see the `Arduino libraries documentation`_.
+
+References
+**********
+
+#. `Arduino-Core-Zephyr GitHub Repository`_
+#. `ArduinoCore-API Repository`_
+#. `Golioth Article: Zephyr + Arduino: a Google Summer of Code story`_
+
+.. target-notes::
+
+.. _Arduino Core API: https://github.com/zephyrproject-rtos/arduino-core-zephyr
+.. _board variants documentation: https://github.com/zephyrproject-rtos/arduino-core-zephyr/blob/main/documentation/variants.md
+.. _Arduino libraries documentation: https://github.com/zephyrproject-rtos/arduino-core-zephyr/blob/main/documentation/arduino_libs.md
+.. _Arduino-Core-Zephyr GitHub Repository: https://github.com/zephyrproject-rtos/arduino-core-zephyr
+.. _ArduinoCore-API Repository: https://github.com/arduino/ArduinoCore-API
+.. _Google Summer of Code 2022 project: https://dhruvag2000.github.io/Blog-GSoC22/
+.. _Golioth Article\: Zephyr + Arduino\: a Google Summer of Code story: https://blog.golioth.io/zephyr-arduino-a-google-summer-of-code-story/
+.. _blinky_arduino sample: https://github.com/zephyrproject-rtos/arduino-core-zephyr/blob/next/samples/blinky_arduino/prj.conf