config: add dynamic init file

* config: add dynamic init file

* added review feedback

* added docs

Kconfig

@@ -73,6 +73,11 @@ menu "Toolchain"
         help
             relative path to the ROMFS root directory
 
+    config BOARD_ADDITIONAL_INIT
+        string "Additional init file"
+        help
+            additional configurable init file to include in the ROMFS
+
     config BOARD_IO
         string "IO board name"
         default "px4_io-v2_default"

ROMFS/CMakeLists.txt

@@ -202,6 +202,31 @@ foreach(board_rc_file ${OPTIONAL_BOARD_RC})
 
 endforeach()
 
+if(config_additional_init)
+	if(EXISTS "${PX4_BOARD_DIR}/init/${config_additional_init}")
+		file(RELATIVE_PATH rc_file_relative ${PX4_SOURCE_DIR} ${PX4_BOARD_DIR}/init/${config_additional_init})
+		message(STATUS "ROMFS:  Adding ${rc_file_relative} -> /etc/init.d/rc.additional_init")
+
+		add_custom_command(
+			OUTPUT
+				${romfs_gen_root_dir}/init.d/rc.additional_init
+				${config_additional_init}.stamp
+			COMMAND ${CMAKE_COMMAND} -E copy_if_different ${PX4_BOARD_DIR}/init/${config_additional_init} ${romfs_gen_root_dir}/init.d/rc.additional_init
+			COMMAND ${CMAKE_COMMAND} -E touch ${config_additional_init}.stamp
+			DEPENDS
+				${PX4_BOARD_DIR}/init/${config_additional_init}
+				romfs_copy.stamp
+			COMMENT "ROMFS: copying ${config_additional_init}"
+		)
+
+		list(APPEND extras_dependencies
+			${config_additional_init}.stamp
+			)
+	else()
+		message(FATAL_ERROR "BOARD_ADDITIONAL_INIT file not found at: ${PX4_BOARD_DIR}/init/${config_additional_init}")
+	endif()
+endif()
+
 
 # board extras
 set(OPTIONAL_BOARD_EXTRAS)

ROMFS/cannode/init.d/rcS

@@ -56,6 +56,17 @@ then
 fi
 unset BOARD_RC_DEFAULTS
 
+#
+# Optional additional init file: rc.additional_init
+#
+set BOARD_RC_ADDITIONAL_INIT ${R}etc/init.d/rc.additional_init
+if [ -f $BOARD_RC_ADDITIONAL_INIT ]
+then
+	echo "Board additional init: ${BOARD_RC_ADDITIONAL_INIT}"
+	. $BOARD_RC_ADDITIONAL_INIT
+fi
+unset BOARD_RC_ADDITIONAL_INIT
+
 #
 # Start system state indicator.
 #

ROMFS/px4fmu_common/init.d/rcS

@@ -217,6 +217,17 @@ else
 	fi
 	unset BOARD_RC_DEFAULTS
 
+	#
+	# Optional additional init file: rc.additional_init
+	#
+	set BOARD_RC_ADDITIONAL_INIT ${R}etc/init.d/rc.additional_init
+	if [ -f $BOARD_RC_ADDITIONAL_INIT ]
+	then
+		echo "Board additional init: ${BOARD_RC_ADDITIONAL_INIT}"
+		. $BOARD_RC_ADDITIONAL_INIT
+	fi
+	unset BOARD_RC_ADDITIONAL_INIT
+
 	# Load airframe configuration based on SYS_AUTOSTART parameter
 	if ! param compare SYS_AUTOSTART 0
 	then

cmake/kconfig.cmake

@@ -339,6 +339,11 @@ if(EXISTS ${BOARD_DEFCONFIG})
 		endif()
 	endif()
 
+	# ADDITIONAL INIT
+	if(ADDITIONAL_INIT)
+		set(config_additional_init ${ADDITIONAL_INIT} CACHE INTERNAL "additional init" FORCE)
+	endif()
+
 	if(UAVCAN_INTERFACES)
 		set(config_uavcan_num_ifaces ${UAVCAN_INTERFACES} CACHE INTERNAL "UAVCAN interfaces" FORCE)
 	endif()

docs/en/concept/system_startup.md

@@ -90,6 +90,8 @@ This is documented below.
 The best way to customize the system startup is to introduce a [new frame configuration](../dev_airframes/adding_a_new_frame.md).
 The frame configuration file can be included in the firmware or on an SD Card.
 
+#### Dynamic customization
+
 If you only need to "tweak" the existing configuration, such as starting one more application or setting the value of a few parameters, you can specify these by creating two files in the `/etc/` directory of the SD Card:
 
 - [/etc/config.txt](#customizing-the-configuration-config-txt): modify parameter values
@@ -106,7 +108,7 @@ If editing on Windows use a suitable editor.
 These files are referenced in PX4 code as `/fs/microsd/etc/config.txt` and `/fs/microsd/etc/extras.txt`, where the root folder of the microsd card is identified by the path `/fs/microsd`.
 :::
 
-#### Customizing the Configuration (config.txt)
+##### Customizing the Configuration (config.txt)
 
 The `config.txt` file can be used to modify parameters.
 It is loaded after the main system has been configured and _before_ it is booted.
@@ -118,7 +120,7 @@ param set-default PWM_MAIN_DIS3 1000
 param set-default PWM_MAIN_MIN3 1120
 ```
 
-#### Starting Additional Applications (extras.txt)
+##### Starting Additional Applications (extras.txt)
 
 The `extras.txt` can be used to start additional applications after the main system boot.
 Typically these would be payload controllers or similar optional custom components.
@@ -145,3 +147,28 @@ The following example shows how to start custom applications:
 
   mandatory_app start     # Will abort boot if mandatory_app is unknown or fails
   ```
+
+#### Additional customization
+
+In rare cases where the desired setup cannot be achieved through frame configuration or dynamic customization,
+you can add a script that will be contained in the binary.
+
+**Note**: In almost all cases, you should use a frame configuration. This method should only be used for
+edge-cases such as customizing `cannode` based boards.
+
+- Add a new init script in `boards/<vendor>/<board>/init` that will run during board startup. For example:
+  ```sh
+  # File: boards/<vendor>/<board>/init/rc.additional
+  param set-default <param> <value>
+  ```
+
+- Add a new board variant in `boards/<vendor>/<board>/<variant>.px4board` that includes the additional script. For example:
+  ```sh
+  # File: boards/<vendor>/<board>/var.px4board
+  CONFIG_BOARD_ADDITIONAL_INIT="rc.additional"
+  ```
+
+- Compile the firmware with your new variant by appending the variant name to the compile target. For example:
+  ```sh
+  make <target>_var
+  ```