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+PX4 Build System
+================
+
+The files in this directory implement the PX4 runtime firmware build system
+and configuration for the standard PX4 boards and software, in conjunction
+with Makefile in the parent directory.
+
+../Makefile
+
+	Top-level makefile for the PX4 build system. This makefile supports
+	building NuttX archives, as well as supervising the building of all
+	of the defined PX4 firmware configurations.
+
+	Try 'make help' in the parent directory for documentation.
+
+firmware.mk
+
+	Manages the build for one specific firmware configuration. 
+	See the comments at the top of this file for detailed documentation.
+
+	Builds modules, builtin command lists and the ROMFS (if configured).
+
+	This is the makefile directly used by external build systems; it can
+	be configured to compile modules both inside and outside the PX4
+	source tree. When used in this mode, at least BOARD, MODULES and 
+	CONFIG_FILE must be set.
+
+module.mk
+
+	Called by firmware.mk to build individual modules.
+	See the comments at the top of this file for detailed documentation.
+
+	Not normally used other than by firmware.mk.
+
+nuttx.mk
+
+	Called by ../Makefile to build or download the NuttX archives.
+
+upload.mk
+
+	Called by ../Makefile to upload files to a target board. Can be used
+	by external build systems as well.
+
+setup.mk
+
+	Provides common path and tool definitions. Implements host system-specific
+	compatibility hacks.
+
+board_<boardname>.mk
+
+	Board-specific configuration for <boardname>. Typically sets CONFIG_ARCH
+	and then includes the toolchain definition for the board.
+
+config_<boardname>_<configname>.mk
+
+	Parameters for a specific configuration on a specific board.
+	The board name is derived from the filename.  Sets MODULES to select
+	source modules to be included in the configuration, may also set
+	ROMFS_ROOT to build a ROMFS and BUILTIN_COMMANDS to include non-module
+	commands (e.g. from NuttX)
+
+toolchain_<toolchainname>.mk
+
+	Provides macros used to compile and link source files.
+	Accepts EXTRADEFINES to add additional pre-processor symbol definitions,
+	EXTRACFLAGS, EXTRACXXFLAGS, EXTRAAFLAGS and EXTRALDFLAGS to pass
+	additional flags to the C compiler, C++ compiler, assembler and linker
+	respectively.
+
+	Defines the COMPILE, COMPILEXX, ASSEMBLE, PRELINK, ARCHIVE and LINK
+	macros that are used elsewhere in the build system.