Add documentation for building and running SOF under Zephyr

SOF can be built as a Zephyr application. This document describes
the process.

Signed-off-by: Guennadi Liakhovetski <[email protected]>

getting_started/build-guide/build-with-zephyr.rst

@@ -0,0 +1,69 @@
+.. _build-with-zephyr:
+
+Build SOF with Zephyr
+#####################
+
+.. contents::
+   :local:
+   :depth: 3
+
+This guide describes the process of building and running |SOF| as a Zephyr
+application.
+
+.. note::
+
+        The example uses ``$ZEPHYR_WORKSPACE`` as the working directory.
+
+Preparation
+***********
+
+The easiest way to build Zephyr is by using its recommended toolchain. Follow
+instructions in the
+`Install a Toolchain <https://docs.zephyrproject.org/latest/getting_started/index.html#install-a-toolchain>`__
+chapter for toolchain installation details.
+
+Check out and build
+*******************
+
+Zephyr uses ``west`` as a source management and building system. Follow the
+Zephyr
+`Getting Started <https://docs.zephyrproject.org/latest/getting_started/index.html#>`__
+guide for dependencies and for ``west`` installation.
+
+Initialize a new ``west`` repository
+
+.. code-block:: bash
+
+    mkdir $ZEPHYR_WORKSPACE
+    cd $ZEPHYR_WORKSPACE
+    west init
+    west update
+
+.. note::
+
+    If you need to checkout a different Zephyr fork or branch you can do something like
+
+.. code-block:: bash
+
+    west init --manifest-url https://github.com/thesofproject/zephyr --manifest-rev intel_adsp_soc_family
+
+This checks out all the Zephyr sources, including |SOF|. After that a firmware
+image can be built and signed:
+
+.. code-block:: bash
+
+    west build -p -d build-apl -b up_squared_adsp zephyr/samples/audio/sof/ -- -DCMAKE_C_FLAGS=-Izephyr/lib/libc/minimal/include/
+    west sign -d build-apl -t rimage -- -k modules/audio/sof/keys/otc_private_key.pem
+
+Running
+*******
+
+After the above a ready image is located at ``build-apl/zephyr/zephyr.ri``, as
+usual it can be copied to the usual firmware location on the target systen, e.g.
+if built natively
+
+.. code-block:: bash
+
+    sudo cp build-apl/zephyr/zephyr.ri /lib/firmware/intel/sof/community/sof-cnl.ri
+
+For firmware log extraction use zephyr/boards/xtensa/up_squared_adsp/tools/logtool.py

getting_started/index.rst

@@ -19,6 +19,7 @@ is always preffered.
    build-guide/build-from-scratch
    build-guide/build-with-docker
    build-guide/build-3rd-party-toolchain
+   build-guide/build-with-zephyr
 
 Setting up SOF on hardware
 **************************