.. _concepts:
.. _vocabulary:

Concepts
--------

This page is meant to introduce you to some of the concepts inherent to
the Apache Mynewt Operating System, and *Newt* the tool that stitches a
project built on Apache Mynewt together.

.. contents::
  :local:
  :depth: 2

Project
~~~~~~~

The project is the base directory of your embedded software tree. It is
a workspace that contains a logical collection of source code, for one
or more of your applications. A project consists of the following items:

-  Project Definition: defines project level dependencies, and
   parameters (located in ``project.yml``)
-  Packages

`Package`_ are described in detail in the section below.

Here is an example project definition file from the default Apache
Mynewt project:

.. code-block:: yaml

    # project.yml
    # <snip>
    project.name: "my_project"

    project.repositories:
        - apache-mynewt-core

    # Use github's distribution mechanism for core ASF libraries.
    # This provides mirroring automatically for us.
    #
    repository.apache-mynewt-core:
        type: github
        vers: 1-latest
        user: apache
        repo: mynewt-core

A couple of things to note in the project definition:

-  ``project.repositories``: Defines the remote repositories that this
   project relies upon.

-  ``repository.apache-mynewt-core``: Defines the repository information
   for the ``apache-mynewt-core`` repository.

-  ``vers=1-latest``: Defines the repository version. This string will
   use the latest stable version in the 'Master' github branch. To use
   the latest version in the master branch, just change it to
   ``vers=0-dev``. Note that this branch might not be stable.

Repositories are versioned collections of packages.

Projects can rely on remote repositories for functionality, and the newt
tool will resolve those remote repositories, and download the correct
version into your local source tree. Newly fetched repositories are put
in the ``repos`` directory of your project, and can be referenced
throughout the system by using the ``@`` specifier.

By default, the ``@apache-mynewt-core`` repository is included in every
project. Apache Mynewt Core contains all the base functionality of the
Apache Mynewt Operating System, including the Real Time Kernel,
Bluetooth Networking Stack, Flash File System, Console, Shell and
Bootloader.

*NOTE:* Any project can be converted into a repository by providing it
with a ``repository.yml`` file and putting it up onto Github. More
information about repositories can be found in the Newt documentation.

Package
~~~~~~~

A package is a collection items that form a fundamental unit in the
Mynewt Operating System. Packages can be:

-  Applications
-  Libraries
-  Compiler definitions
-  Targets

A package is identified by having a ``pkg.yml`` file in it's base
directory. Here is a sample ``pkg.yml`` file for the blinky applicaton:

.. code-block:: yaml

    # pkg.yml
    # <snip>
    pkg.name: apps/blinky
    pkg.type: app
    pkg.description: Basic example application which blinks an LED.
    pkg.author: "Apache Mynewt <dev@mynewt.apache.org>"
    pkg.homepage: "http://mynewt.apache.org/"
    pkg.keywords:

    pkg.deps:
        - "@apache-mynewt-core/libs/os"
        - "@apache-mynewt-core/hw/hal"
        - "@apache-mynewt-core/libs/console/full"

Packages have a few features worth noting:

-  Dependencies: Packages can rely upon other packages, and when they do
   they will inherit their functionality (header files, library
   definitions, etc.)
-  APIs: Packages can export named APIs, and they can require that
   certain APIs be present, in order to compile.

Everything that newt knows about within a project's directory is a
package. This makes it very clean and easy to write re-usable
components, which can describe their Dependencies and APIs to the rest
of the system.

.. _mynewt-target:

Target
~~~~~~

A target in Apache Mynewt is very similar to a target in *make*. It is
the collection of parameters that must be passed to Newt in order to
generate a reproducible build. A target represents the top of the build
tree, and any packages or parameters specified at the target level,
cascade down to all dependencies.

Targets are also packages, and are stored in the ``targets/`` directory
at the base of your project. Most targets consist of:

-  ``app``: The application to build.
-  ``bsp``: The board support package to combine with that application
-  ``build_profile``: Either ``debug`` or ``optimized``.

Targets can also have additional items specified, including:

-  ``aflags``: Any additional assembler flags you might want to specify
   to the build.
-  ``cflags``: Any additional compiler flags you might want to specify
   to the build.
-  ``lflags``: Any additional linker flags you might want to specify to
   the build.

In order to create and manipulate targets, the *newt* tool offers a set
of helper commands, you can find more information about these by
issuing:

.. code-block:: console

    $ newt target
    Usage:
      newt target [flags]
      newt target [command]

    Available Commands:
      amend       Add, change, or delete values for multi-value target variables
      cmake
      config      View or populate a target's system configuration
      copy        Copy target
      create      Create a target
      delete      Delete target
      dep         View target's dependency graph
      revdep      View target's reverse-dependency graph
      set         Set target configuration variable
      show        View target configuration variables

    Global Flags:
      -h, --help              Help for newt commands
      -j, --jobs int          Number of concurrent build jobs (default 2)
      -l, --loglevel string   Log level (default "WARN")
      -o, --outfile string    Filename to tee output to
      -q, --quiet             Be quiet; only display error output
      -s, --silent            Be silent; don't output anything
      -v, --verbose           Enable verbose output when executing commands

    Use "newt target [command] --help" for more information about a command.

Configuration
~~~~~~~~~~~~~

Additional help topics:

.. code-block:: console

    $ newt target config show <target-name>
    ...
    * PACKAGE: sys/stats
      * Setting: STATS_CLI
        * Description: Expose the "stat" shell command.
        * Value: 0
      * Setting: STATS_NAMES
        * Description: Include and report the textual name of each statistic.
        * Value: 0
      * Setting: STATS_NEWTMGR
        * Description: Expose the "stat" newtmgr command.
        * Value: 0
    ...
    $