doc: build: flashing: Add documentation

Adds documentation on the new flashing configuration system

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

doc/build/flashing/configuration.rst

@@ -0,0 +1,106 @@
+.. _flashing-soc-board-config:
+
+Flashing configuration
+######################
+
+Zephyr supports setting up configuration for flash runners (invoked from
+:ref:`west flash<west-flashing>`) which allows for customising how commands are used when
+programming boards. This configuration is used for :ref:`sysbuild` projects and allows for
+configuring when commands are ran for groups of board targets. As an example: a multi-core SoC
+might want to only allow the ``--erase`` argument to be used once for all of the cores in the SoC
+which would prevent multiple erase tasks running in a single ``west flash`` invocation, which
+could wrongly clear the memory which is used by the other images being programmed.
+
+Priority
+********
+
+Flashing configuration is singular, it will only be read from a single location, this
+configuration can reside in the following files starting with the highest priority:
+
+ * ``soc.yml`` (in soc folder)
+ * ``board.yml`` (in board folder)
+
+Configuration
+*************
+
+Configuration is applied in the yml file by using a ``runners`` map with a single ``run_once``
+child, this then contains a map of commands as they would be provided to the flash runner e.g.
+``--reset`` followed by a list which specifies the settings for each of these commands (these
+are grouped by flash runner, and by qualifiers/boards). Commands have associated runners that
+they apply to using a ``runners`` list value, this can contain ``all`` if it applies to all
+runners, otherwise must contain each runner that it applies to using the runner-specific name.
+Groups of board targets can be specified using the ``groups`` key which has a list of board
+target sets. Board targets are regular expression matches, for ``soc.yml`` files each set of
+board targets must be in a ``qualifiers`` key (only regular expression matches for board
+qualifiers are allowed, board names must be omitted from these entries). For ``board.yml``
+files each set of board targets must be in a ``boards`` key, these are lists containing the
+matches which form a singular group. A final parameter ``run`` can be set to ``first`` which
+means that the command will be ran once with the first image flashing process per set of board
+targets, or to ``last`` which will be ran once for the final image flash per set of board targets.
+
+An example flashing configuration for a ``soc.yml`` is shown below in which the ``--recover``
+command will only be used once for any board targets which used the nRF5340 SoC application or
+network CPU cores, and will only reset the network or application core after all images for the
+respective core have been flashed.
+
+.. code-block:: yaml
+
+  runners:
+    run_once:
+      '--recover':
+        - run: first
+          runners:
+            - nrfjprog
+          groups:
+            - qualifiers:
+                - nrf5340/cpunet
+                - nrf5340/cpuapp
+                - nrf5340/cpuapp/ns
+      '--reset':
+        - run: last
+          runners:
+            - nrfjprog
+            - jlink
+          groups:
+            - qualifiers:
+                - nrf5340/cpunet
+            - qualifiers:
+                - nrf5340/cpuapp
+                - nrf5340/cpuapp/ns
+        # Made up non-real world example to show how to specify different options for different
+        # flash runners
+        - run: first
+          runners:
+            - some_other_runner
+          groups:
+            - qualifiers:
+                - nrf5340/cpunet
+            - qualifiers:
+                - nrf5340/cpuapp
+                - nrf5340/cpuapp/ns
+
+Usage
+*****
+
+Commands that are supported by flash runners can be used as normal when flashing non-sysbuild
+applications, the run once configuration will not be used. When flashing a sysbuild project with
+multiple images, the flash runner run once configuration will be applied.
+
+For example, building the :zephyr:code-sample:`smp-svr` sample for the nrf5340dk which will
+include MCUboot as a secondary image:
+
+.. code-block:: console
+
+   cmake -GNinja -Sshare/sysbuild/ -Bbuild -DBOARD=nrf5340dk/nrf5340/cpuapp -DAPP_DIR=samples/subsys/mgmt/mcumgr/smp_svr
+   cmake --build build
+
+Once built with an nrf5340dk connected, the following command can be used to flash the board with
+both applications and will only perform a single device recovery operation when programming the
+first image:
+
+.. code-block:: console
+
+   west flash --recover
+
+If the above was ran without the flashing configuration, the recovery process would be ran twice
+and the device would be unbootable.

doc/build/flashing/index.rst

@@ -0,0 +1,9 @@
+.. _flashing:
+
+Flashing
+########
+
+.. toctree::
+   :maxdepth: 1
+
+   configuration.rst

doc/build/index.rst

@@ -15,3 +15,4 @@ Build and Configuration Systems
    zephyr_cmake_package.rst
    sysbuild/index.rst
    version/index.rst
+   flashing/index.rst