.. _module-pw_build_mcuxpresso:

===================
pw_build_mcuxpresso
===================

The ``pw_build_mcuxpresso`` module provides helper utilities for building a
target based on an NXP MCUXpresso SDK.

The GN build files live in ``third_party/mcuxpresso`` but are documented here.
The rationale for keeping the build files in ``third_party`` is that code
depending on an MCUXpresso SDK can clearly see that their dependency is on
third party, not pigweed code.

-----------------------
Using an MCUXpresso SDK
-----------------------
An MCUXpresso SDK consists of a number of components, each of which has a set
of sources, headers, preprocessor defines, and dependencies on other
components. These are all described in an XML "manifest" file included in the
SDK package.

To use the SDK within a Pigweed project, the set of components you need must be
combined into a library that you can depend on. This library will include all of
the sources and headers, along with necessary preprocessor defines, for those
components and their dependencies.

Optional components
===================
Including components will include all of their required dependencies. Where the
components you include have optional dependencies, they must be satisfied by the
set of components you include otherwise the library generation will fail with an
error.

Excluding components
====================
Components can be excluded from the generated source set, for example to
suppress errors about optional dependencies your project does not need, or to
prevent an unwanted component dependency from being introduced into your
project.

mcuxpresso_builder
==================
``mcuxpresso_builder`` is a utility installed into the environment that is used
by the GN build scripts in ``third_party/mcuxpresso``, or directly by you to
generate rules for the Bazel build.

Usage is documented for each build system in the relevant section.

------------
The GN build
------------
Using an MCUxpresso SDK within a Pigweed project that uses the GN Build system
involves the creation of one or more ``pw_source_set`` targets you can depend on
in your executable targets.

These source sets sets are defined using the ``pw_mcuxpresso_sdk`` template.
Provide the path to the ``manifest`` XML, along with the names of the components
you wish to ``include``.

.. code-block:: text

   import("$dir_pw_third_party/mcuxpresso/mcuxpresso.gni")

   pw_mcuxpresso_sdk("sample_project_sdk") {
     manifest = "$dir_pw_third_party/mcuxpresso/evkmimxrt595/EVK-MIMXRT595_manifest_v3_8.xml"
     include = [
       "component.serial_manager_uart.MIMXRT595S",
       "project_template.evkmimxrt595.MIMXRT595S",
       "utility.debug_console.MIMXRT595S",
     ]
   }

   pw_executable("hello_world") {
     sources = [ "hello_world.cc" ]
     deps = [ ":sample_project_sdk" ]
   }

To exclude components, provide the list to ``exclude`` as an argument to the
template. For example to replace the FreeRTOS kernel bundled with the MCUXpresso
SDK with the Pigweed third-party target:

.. code-block:: text

   pw_mcuxpresso_sdk("freertos_project_sdk") {
     // manifest and includes ommitted for clarity
     exclude = [ "middleware.freertos-kernel.MIMXRT595S" ]
     public_deps = [ "$dir_pw_third_party/freertos" ]
   }

Introducing dependencies
========================
As seen above, the generated source set can have dependencies added by passing
the ``public_deps`` (or ``deps``) arguments to the template.

You can also pass the ``allow_circular_includes_from``, ``configs``, and
``public_configs`` arguments to augment the generated source set.

For example it is very common to replace the ``project_template`` component with
a source set of your own that provides modified copies of the files from the
SDK.

To resolve circular dependencies, in addition to the generated source set, two
configs named with the ``__defines`` and ``__includes`` suffixes on the template
name are generated, to provide the preprocessor defines and include paths that
the source set uses.

.. code-block:: text

   pw_mcuxpresso_sdk("my_project_sdk") {
     manifest = "$dir_pw_third_party/mcuxpresso/evkmimxrt595/EVK-MIMXRT595_manifest_v3_8.xml"
     include = [
       "component.serial_manager_uart.MIMXRT595S",
       "utility.debug_console.MIMXRT595S",
     ]
     public_deps = [ ":my_project_config" ]
     allow_circular_includes_from = [ ":my_project_config" ]
   }

   pw_source_set("my_project_config") {
     sources = [ "board.c", "clock_config.c", "pin_mux.c" ]
     public = [ "board.h", "clock_config.h", "pin_mux.h "]
     public_configs = [
       ":my_project_sdk__defines",
       ":my_project_sdk__includes"
     ]
   }

mcuxpresso_builder
==================
For the GN build, this utility is invoked by the ``pw_mcuxpresso_sdk`` template.
You should only need to interact with ``mcuxpresso_builder`` directly if you are
doing something custom.

The ``gn`` subcommand outputs a GN scope describing the result of expanding the
set of included and excluded components.

The ``--prefix`` option specifies the GN location of the SDK files.

.. code-block:: bash

   mcuxpresso_builder gn /path/to/manifest.xml \
       --include project_template.evkmimxrt595.MIMXRT595S \
       --include utility.debug_console.MIMXRT595S \
       --include component.serial_manager_uart.MIMXRT595S \
       --exclude middleware.freertos-kernel.MIMXRT595S \
       --prefix //path/to/sdk

---------------
The Bazel build
---------------
To use an MCUxpresso SDK within a Pigweed project that uses tha Bazel build
system, you must use the ``mcuxpresso_builder`` tool directly and place its
output in ``BUILD`` or ``BUILD.bazel`` files yourself.

Provide the path to the manifest XML, the ``--name`` of the ``cc_library`` to
create, along with the names of the components you wish to ``--include`` or
``--exclude``.

.. code-block:: bash

   mcuxpresso_builder bazel /path/to/manifest.xml \
       --name example_sdk \
       --include project_template.evkmimxrt595.MIMXRT595S \
       --include utility.debug_console.MIMXRT595S \
       --include component.serial_manager_uart.MIMXRT595S \
       --exclude middleware.freertos-kernel.MIMXRT595S


Place the resulting output in a ``BUILD`` file, and then modify your
``WORKSPACE`` to associate this build file with the path to the MCUxpresso SDK
checkout.

.. code-block:: python

   new_local_repository(
       name = "mcuxpresso_sdk",
       build_file = "//third_party/mcuxpresso_sdk/BUILD",
       path = "third_party/evkmimxrt595/sdk",
   )

To add other dependencies, compiler definitions, etc. it is recommended that
you do so by creating a new target, and add a dependency to it, rather than
modifying the generated targets.