Start of documentation for adding boards (#3395)

* Start of documentation for adding boards

* Update path

* Add information to common_board.h

---------

Co-authored-by: Florian Sansou <florian.sansou@enac.fr>

doc/sphinx/source/developer_guide/index_developer.rst

@@ -15,4 +15,5 @@ TBD
     abi
     logging
     debug
+    new_board
 

doc/sphinx/source/developer_guide/new_board.rst

@@ -0,0 +1,72 @@
+.. developer_guide new_board
+
+===========================
+How to support a new board
+===========================
+
+To integrate a new card, it is necessary to create several files.
+
+.. _board_dir:
+
+Board directory
+----------------
+
+You'll find the complete set of boards in `sw/airborne/boards/ <https://github.com/paparazzi/paparazzi/tree/master/sw/airborne/boards/>`_. You can create a directory (and sub-directories) for your board. 
+
+.. note::
+    You need to define a structure like ``sw/airborne/boards/<manufacturer>/<board>/<vx.x>/``.
+
+Within this directory, you must have :
+
+1. A ``Makefile`` to generate the board.h file from board.cfg using `boardGen.pl <https://github.com/alex31/chibios_enac_various_common/blob/master/TOOLS/boardGen.pl>`_.
+2. A ``board.cfg`` containing the definition of the pins used (see `documentation <https://github.com/alex31/chibios_enac_various_common/blob/master/TOOLS/DOC/boardGen.pdf>`_). It is preferable to use the generic pin names defined in the ``common_board.h`` in the directory `sw/airborne/arch/chibios <https://github.com/paparazzi/paparazzi/blob/master/sw/airborne/arch/chibios/common_board.h>`_. Any information that is not common to the various boards can be inserted in the HEADER section of the ``board.cfg``.
+3. A ``board.h`` file, which is the result of running ``make`` in this directory (this file must not be modified; you have to run `boardGen.pl` for any change in `board.cfg`).
+4. A ``mcuconf_board.h`` file, which defines the microcontroller's configuration (clock, peripherals, etc.). If the microcontroller is supported by ChibiOS, an example can be found in `sw/ext/chibios/demos/STM32/<board_name>/cfg/mcuconf.h <https://github.com/paparazzi/ChibiOS/tree/paparazzi/demos/STM32>`_.
+
+
+.. _linker_script:
+
+Linker Script
+----------------
+
+To compile, you need the linker script developed for your microcontroller.
+Check the directory `sw/airborne/arch/chibios <https://github.com/paparazzi/paparazzi/tree/master/sw/airborne/arch/chibios>`_ to see if the linker script corresponding to your microcontroller is already present. If not, retrieve the linker script from `ChibiOS <https://github.com/paparazzi/ChibiOS/tree/paparazzi/os/common/startup/ARMCMx/compilers/GCC/ld>`_.
+
+
+
+Board makefile
+----------------
+In the directory `conf/boards/ <https://github.com/paparazzi/paparazzi/tree/master/conf/boards>`_, you'll find the Makefile used for compiling.
+It is necessary to create a new Makefile for each board, named ``<board_name>_<version>.makefile`` (e.g. ``tawaki_2.0.makefile``).
+The name of this file will be the name used in the airframe file when defining the target:
+
+.. code-block:: xml
+    
+     <target name="ap" board="<board_name>_<version>">
+     </target>
+
+In this Makefile, it is necessary to configure several points :
+
+* ``BOARD_DIR`` must point to the directory defined in :ref:`board_dir` with relative path from `sw/airborne/boards <https://github.com/paparazzi/paparazzi/tree/master/sw/airborne/boards>`_ and ``BOARD_CFG`` must point to the file `sw/airborne/arch/chibios/common_board.h <https://github.com/paparazzi/paparazzi/blob/master/sw/airborne/arch/chibios/common_board.h>`_.
+* check floating-point unit type to configure ``USE_FPU_OPT`` (single-precision and a double-precision).
+* modify the linker script in ``CHIBIOS_BOARD_LINKER`` to use the correct one (see :ref:`linker_script`).
+* modify the architecture used by ``CHIBIOS_BOARD_PLATFORM`` and ``CHIBIOS_BOARD_STARTUP``.
+* this file can also contain LED, UART, radio and actuator default definitions.
+
+
+Using this Makefile, we need to create an XML file defining the board. This file must have the same name has the makefile ``<board_name>_<version>.xml`` and located in `conf/module/boards <https://github.com/paparazzi/paparazzi/tree/master/conf/modules/boards>`_.
+
+
+Board module
+----------------
+
+It's very useful to define a module in `conf/module/ <https://github.com/paparazzi/paparazzi/tree/master/conf/modules/>`_, naming it board_****.xml, to load all the sensor modules on board. This is also an opportunity to finish configuring the communication ports with the sensors.
+
+.. note::
+    It's important to fill in the header of this file, as it represents the documentation for this board.  
+
+
+Airframe test
+----------------
+
+When integrating a new board, you can define an airframe file in `conf/airframes/test_boards <https://github.com/paparazzi/paparazzi/tree/master/conf/airframes/test_boards>`_.