cmake: add support for out-of-tree modules via EXTERNAL_MODULES_LOCATION variable

CMakeLists.txt

@@ -146,6 +146,7 @@ set_property(CACHE CONFIG PROPERTY STRINGS ${configs})
 set(THREADS "4" CACHE STRING
 	"number of threads to use for external build processes")
 set(DEBUG_PORT "/dev/ttyACM0" CACHE STRING "debugging port")
+set(EXTERNAL_MODULES_LOCATION "" CACHE STRING "External modules source location")
 
 #=============================================================================
 # configuration
@@ -371,6 +372,24 @@ foreach(driver ${config_df_driver_list})
 	message("Adding DF driver: ${driver}")
 endforeach()
 
+#=============================================================================
+# external modules
+#
+if(NOT EXTERNAL_MODULES_LOCATION STREQUAL "")
+	message(STATUS "External modules: ${EXTERNAL_MODULES_LOCATION}")
+	add_subdirectory("${EXTERNAL_MODULES_LOCATION}/src" external_modules_src)
+
+	set(config_module_list_external_expanded)
+	foreach(external_module ${config_module_list_external})
+		list(APPEND config_module_list_external_expanded
+			${EXTERNAL_MODULES_LOCATION}/src/${external_module})
+	endforeach()
+	set(config_module_list
+		${config_module_list}
+		${config_module_list_external_expanded}
+		)
+endif()
+
 #=============================================================================
 # subdirectories
 #

Makefile

@@ -114,6 +114,12 @@ else
 	BUILD_DIR_SUFFIX :=
 endif
 
+# additional config parameters passed to cmake
+CMAKE_ARGS :=
+ifdef EXTERNAL_MODULES_LOCATION
+	CMAKE_ARGS := -DEXTERNAL_MODULES_LOCATION:STRING=$(EXTERNAL_MODULES_LOCATION)
+endif
+
 SRC_DIR := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
 
 # Functions
@@ -122,7 +128,7 @@ SRC_DIR := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
 define cmake-build
 +@$(eval BUILD_DIR = $(SRC_DIR)/build_$@$(BUILD_DIR_SUFFIX))
 +@if [ $(PX4_CMAKE_GENERATOR) = "Ninja" ] && [ -e $(BUILD_DIR)/Makefile ]; then rm -rf $(BUILD_DIR); fi
-+@if [ ! -e $(BUILD_DIR)/CMakeCache.txt ]; then mkdir -p $(BUILD_DIR) && cd $(BUILD_DIR) && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1) || (cd .. && rm -rf $(BUILD_DIR)); fi
++@if [ ! -e $(BUILD_DIR)/CMakeCache.txt ]; then mkdir -p $(BUILD_DIR) && cd $(BUILD_DIR) && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1) $(CMAKE_ARGS) || (cd .. && rm -rf $(BUILD_DIR)); fi
 +@echo "PX4 CONFIG: $(BUILD_DIR)"
 +@$(PX4_MAKE) -C "$(BUILD_DIR)" $(PX4_MAKE_ARGS) $(ARGS)
 endef

cmake/common/px4_base.cmake

@@ -231,6 +231,7 @@ endfunction()
 #			[ COMPILE_FLAGS <list> ]
 #			[ INCLUDES <list> ]
 #			[ DEPENDS <string> ]
+#			[ EXTERNAL ]
 #			)
 #
 #	Input:
@@ -244,6 +245,7 @@ endfunction()
 #		SRCS			: source files
 #		INCLUDES		: include directories
 #		DEPENDS			: targets which this module depends on
+#		EXTERNAL		: flag to indicate that this module is out-of-tree
 #
 #	Output:
 #		Static library with name matching MODULE.
@@ -263,9 +265,14 @@ function(px4_add_module)
 		NAME px4_add_module
 		ONE_VALUE MODULE MAIN STACK STACK_MAIN STACK_MAX PRIORITY
 		MULTI_VALUE COMPILE_FLAGS LINK_FLAGS SRCS INCLUDES DEPENDS
+		OPTIONS EXTERNAL
 		REQUIRED MODULE
 		ARGN ${ARGN})
 
+	if(EXTERNAL)
+		px4_mangle_name("${EXTERNAL_MODULES_LOCATION}/src/${MODULE}" MODULE)
+	endif()
+
 	px4_add_library(${MODULE} STATIC EXCLUDE_FROM_ALL ${SRCS})
 
 	# set defaults if not set