doc: Add Application Directory Structure content to the App. Primer.

Adds the information regarding the application's directory structure
expected by the kernel and the build system. It includes how to create
a Makefile for the application's directory.

Change-Id: I4911bd86205831d7cdf1dea6095a9090ba9122b9
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>

doc/application/apps_structure.rst

@@ -0,0 +1,167 @@
+.. _apps_structure:
+
+Application Development Directory Structure
+###########################################
+
+Each application resides in a uniquely-named application
+directory created by the developer, typically, in the developer's
+workspace directory. The application developer also creates a
+:file:`src` directory for the application's source code.
+
+.. note::
+
+   The |codename| either supplies or generates all other application
+   directories.
+
+Procedures
+**********
+
+* `create_directory_structure`_
+
+* `create_src_makefile`_
+
+.. _create_directory_structure:
+
+Creating an Application and Source Code Directory using the CLI
+===============================================================
+
+Create one directory for your application and another for the application's
+source code; this makes it easier to organize directories and files in the
+structure that the kernel expects.
+
+Before You Begin
+----------------
+
+* The environment variable must be set for each console terminal using
+  :ref:`Setting the Environment Variables`.
+
+Steps
+-----
+
+1. Create an application directory structure outside of the kernel's
+   installation directory tree. Often this is your workspace directory.
+
+ a) In a Linux console, navigate to a location where you want your
+    applications to reside.
+
+ b) Create the application's directory, enter:
+
+   .. code-block:: console
+
+      $ mkdir application_name
+
+   .. note::
+
+      This directory and the path to it, are referred to in the documentation
+      as :file:`~/appDir`.
+
+2. Create a source code directory in your :file:`~/appDir`, enter:
+
+   .. code-block:: console
+
+      $ mkdir src
+
+   The source code directory :file:`~/appDir/src` is created.
+
+   .. code-block:: console
+
+      -- appDir
+         |-- src
+
+.. _create_src_makefile:
+
+Creating an Application Makefile
+================================
+
+Create an application Makefile to define basic information such as the kernel
+type, microkernel or nanokernel, and the platform configuration used by the
+application. The build system uses the Makefile to build an image with both
+the application and the kernel libraries called either
+:file:`microkernel.elf` or :file:`nanokernel.elf`.
+
+Before You Begin
+----------------
+
+* Be familiar with the standard GNU Make language.
+
+* Be familiar with the platform configuration used for your application
+  and, if it is a custom platform configuration, where it is located.
+
+* Set the environment variable for each console terminal using
+  :ref:`set_environment_variables`.
+
+Steps
+-----
+
+1. In the :file:`appDir` directory, create a Makefile. Enter:
+
+   .. code-block:: bash
+
+      $ touch Makefile
+
+2. Open the :file:`Makefile` and add the following mandatory
+   entries using any standard text editor.
+
+   .. note::
+
+      Ensure that there is a space after each ``=``.
+
+   a) Add the kernel type on a new line:
+
+      .. code-block:: make
+
+         KERNEL_TYPE = micro|nano
+
+      Either micro or nano, short for microkernel or
+      nanokernel respectively.
+
+   b) Add the name of the platform configuration for your application on a
+      new line:
+
+      .. code-block:: make
+
+         PLATFORM_CONFIG ?= platform_configuration_name
+
+      The supported platforms can be found in :ref:`platform`.
+
+   c) Add the name of the default kernel configuration file for your
+      application on a new line:
+
+      .. code-block:: make
+
+         CONF_FILE = prj.conf
+
+      The default name is :file:`prj.conf`. If you are not using the default
+      name, this entry must match the filename of the :file:`.conf` file you
+      are using.
+
+   d) For microkernel applications, add the name of the MDEF for your
+      application:
+
+      .. code-block:: make
+
+         MDEF_FILE = prj.mdef
+
+      The default name is :file:`prj.mdef`. If you are not using the default
+      name, this entry must match the filename of the :file:`.mdef` file you
+      are using.
+
+   e) Include the mandatory :file:`Makefile` fragments on a new
+      line:
+
+      .. code-block:: make
+
+         include ${ZEPHYR_BASE}/Makefile.inc
+
+3. Save and close the :file:`Makefile`.
+
+Example Makefile
+----------------
+
+.. code-block:: make
+
+   KERNEL_TYPE = micro
+   PLATFORM_CONFIG ?= basic_atom
+   CONF_FILE = prj.conf
+   MDEF_FILE = prj.mdef
+   include ${ZEPHYR_BASE}/Makefile.inc