Newt Tool Guide
---------------

.. toctree::
   :hidden:
   :titlesonly:

   newt_operation
   newt_ops
   install/index

Introduction
~~~~~~~~~~~~

Newt is a smart build and package management system for embedded
contexts. It is a single tool that accomplishes both the following
goals:

-  source package management
-  build, debug and install.

Rationale
~~~~~~~~~

In order for the Mynewt operating system to work well for constrained
environments across the many different types of micro-controller
applications (from doorbells to medical devices to power grids), a
system is needed that lets you select which packages to install and
which packages to build.

The build systems for embedded devices are often fairly complicated and
not well served for this purpose. For example, autoconf is designed for
detecting system compatibility issues but not well suited when it comes
to tasks like:

-  Building for multiple targets
-  Deciding what to build in and what not to build in
-  Managing dependencies between components

Fortunately, solutions addressing these very issues can be found in
source package management systems in higher level languages such as
Javascript (Node), Go, PHP and Ruby. We decided to fuse their source
management systems with a make system built for embedded systems and
create Newt.

Build System
~~~~~~~~~~~~

A good build system must allow the user to take a few common steps while
developing embedded applications:

-  Generate full flash images
-  Download debug images to a target board using a debugger
-  Conditionally compile libraries & code based upon build settings

Newt can read a directory tree, build a dependency tree, and emit the
right build artifacts. An example newt source tree is in
mynewt-blinky/develop:

.. code-block:: console

  $ tree -L 3 .
  ├── DISCLAIMER
  ├── LICENSE
  ├── NOTICE
  ├── README.md
  ├── apps
  │ └── blinky
  │ ├── pkg.yml
  │ └── src
  ├── project.yml
  └── targets
      ├── my_blinky_sim
      │ ├── pkg.yml
      │ └── target.yml
      └── unittest
          ├── pkg.yml
          └── target.yml

  6 directories, 10 files

When Newt sees a directory tree that contains a "project.yml" file, it is smart enough to recognize it as the base directory of a project, and
automatically builds a package tree. It also recognizes two important package directories in the package tree - "apps" and "targets".
More on these directories in :doc:`newt_operation`.

When Newt builds a target, it recursively resolves all package dependencies, and generates artifacts that are placed in the
bin/targets/<target-name>/app/apps/<app-name> directory, where the bin directory is under the project base directory,
``target-name`` is the name of the target, and ``app-name`` is the name of the application. For our example ``my_blinky_sim`` is the
name of the target and ``blinky`` is the name of the application. The ``blinky.elf`` executable is stored in the
bin/targets/my_blinky_sim/app/apps/blinky directory as shown in the source tree:

.. code-block:: console

  $ tree -L 6 bin/
  bin/
  └── targets
      ├── my_blinky_sim
      │   ├── app
      │   │   ├── apps
      │   │   │   └── blinky
      │   │   │       ├── apps
      │   │   │       ├── apps_blinky.a
      │   │   │       ├── apps_blinky.a.cmd
      │   │   │       ├── blinky.elf
      │   │   │       ├── blinky.elf.cmd
      │   │   │       ├── blinky.elf.dSYM
      │   │   │       ├── blinky.elf.lst
      │   │   │       └── manifest.json
      │   │   ├── hw
      │   │   │   ├── bsp
      │   │   │   │   └── native
      │   │   │   ├── drivers
      │   │   │   │   └── uart
      │   │   │   ├── hal
      │   │   │   │   ├── hw_hal.a
      │   │   │   │   ├── hw_hal.a.cmd
      │   │   │   │   └── repos

  <snip>

More operations using Newt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once a target has been built, Newt allows additional operations on the target.

* **load**: Download built target to board
* **debug**: Open debugger session to target
* **size**: Get size of target components
* **create-image**: Add image header to the binary image
* **run**: Build, create image, load, and finally open a debug session with the target
* **target**: Create, delete, configure, and query a target

For more details on how Newt works, go to :doc:`newt_operation`.

Source Management and Repositories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The other major element of the Newt tool is the ability to create reusable source distributions from a collection of code.
**A project can be a reusable container of source code.** In other words, projects can be versioned and redistributed, not packages.
A project bundles together packages that are typically needed to work together in a product e.g. RTOS core, filesystem APIs, and networking stack.

A project that has been made redistributable is known as a **repository**.
Repositories can be added to your local project by adding them into your project.yml file.  Here is an example of the blinky
project's yml file which relies on apache-mynewt-core:

.. code-block:: console

  $ more project.yml
  <snip>
  project.repositories:
        - apache-mynewt-core

  repository.apache-mynewt-core:
        type: github
        vers: 1-latest
        user: apache
        repo: incubator-mynewt-core

When you specify this repository in the blinky's project file, you can then use the Newt tool to install dependencies:

.. code-block:: console

  $ newt install
  Downloading repository description for apache-mynewt-core... success!
  Downloading repository incubator-mynewt-core (branch: develop) at https://github.com/apache/incubator-mynewt-core.git
  Cloning into '/var/folders/7l/7b3w9m4n2mg3sqmgw2q1b9p80000gn/T/newt-repo814721459'...
  remote: Counting objects: 17601, done.
  remote: Compressing objects: 100% (300/300), done.
  remote: Total 17601 (delta 142), reused 0 (delta 0), pack-reused 17284
  Receiving objects: 100% (17601/17601), 6.09 MiB \| 3.17 MiB/s, done.
  Resolving deltas: 100% (10347/10347), done.
  Checking connectivity... done.
  Repos successfully installed

Newt will install this repository in the <project>/repos directory.  In the case of blinky, the directory structure ends up looking like:

.. code-block:: console

  $ tree -L 2
  .
  ├── DISCLAIMER
  ├── LICENSE
  ├── NOTICE
  ├── README.md
  ├── apps
  │   └── blinky
  ├── project.state
  ├── project.yml
  ├── repos
  │   └── apache-mynewt-core
  └── targets
       ├── my_blinky_sim
       └── unittest

In order to reference the installed repositories in packages, the "@" notation should be specified in the repository
specifier.  As an example, the apps/blinky application has the following dependencies in its pkg.yml file. This tells
the build system to look in the base directory of repos/apache-mynewt-core for the ``kernel/os``, ``hw/hal``, and ``sys/console/full`` packages.

.. code-block:: console

  $ more apps/blinky/pkg.yml
  pkg.deps:
    - "@apache-mynewt-core/kernel/os"
    - "@apache-mynewt-core/hw/hal"
    - "@apache-mynewt-core/sys/console/full"

Newt has the ability to autocomplete within ``bash``. The following
instructions allow MAC users to enable autocomplete within ``bash``.

1. Install the autocomplete tools for bash via
   ``brew install bash-completion``
2. Tell your shell to use newt for autocompletion of newt via
   ``complete -C "newt complete" newt``. You can add this to your
   .bashrc or other init file to have it automatically set for all bash
   shells.

Notes:
~~~~~~

1. Autocomplete will give you flag hints, but only if you type a '-'.
2. Autocomplete will not give you completion hints for the flag
   arguments (those optional things after the flag like ``-l DEBUG``)
3. Autocomplete uses newt to parse the project to find targets and libs.