Break up the firmware build into a 'make export' phase for NuttX on a per-board basis, and then a separate per-config phase that allows us to avoid re-building NuttX all the time, and ship more than one firmware config for a given board.

This is a first cut; it builds one firmware for each of FMU and IO.

makefiles/firmware.mk

@@ -0,0 +1,71 @@
+#
+# Generic Makefile for PX4 firmware.
+#
+# Currently this assumes that we're just compiling SRCS
+# and then linking the whole thing together.
+#
+
+#
+# Work out where this file is, so we can find other makefiles in the
+# same directory.
+#
+export PX4_MK_INCLUDE	?= $(dir $(lastword $(MAKEFILE_LIST)))
+
+#
+# Use the linker script from the NuttX export
+#
+LDSCRIPT		 = $(WORK_DIR)/nuttx-export/build/ld.script
+
+#
+# Add directories from the NuttX export to the relevant search paths
+#
+INCLUDE_DIRS		+= $(WORK_DIR)/nuttx-export/include
+LIB_DIRS		+= $(WORK_DIR)/nuttx-export/libs
+LIBS			+= -lapps -lnuttx
+
+#
+# Things that, if they change, might affect everything
+#
+GLOBAL_DEPS		+= $(MAKEFILE_LIST)
+
+#
+# Include the platform configuration
+#
+include $(PX4_MK_INCLUDE)/$(PLATFORM).mk
+
+#
+# What we're going to build
+#
+PRODUCT_BIN		 = $(WORK_DIR)/firmware.bin
+PRODUCT_SYM		 = $(WORK_DIR)/firmware.sym
+PRODUCTS		 = $(PRODUCT_BIN) $(PRODUCT_SYM)
+
+.PHONY:			all
+all:			$(PRODUCTS)
+
+#
+# Rules for building objects
+#
+OBJS			 = $(foreach src,$(SRCS),$(WORK_DIR)/$(src).o)
+
+$(filter %.c.o,$(OBJS)): $(WORK_DIR)/%.c.o: %.c
+	@echo compile $<
+	@mkdir -p $(dir $@)
+	$(call COMPILE,$<,$@)
+
+$(filter %.cpp.o,$(OBJS)): $(WORK_DIR)/%.cpp.o: %.cpp
+	@mkdir -p $(dir $@)
+	$(call COMPILEXX,$<,$@)
+
+$(filter %.S.o,$(OBJS)): $(WORK_DIR)/%.S.o: %.S
+	@mkdir -p $(dir $@)
+	$(call ASSEMBLE,$<,$@)
+
+-include $(DEP_INCLUDES)
+
+$(PRODUCT_BIN):		$(PRODUCT_SYM)
+	$(call SYM_TO_BIN,$<,$@)
+
+$(PRODUCT_SYM):		$(OBJS) $(GLOBAL_DEPS) $(LINK_DEPS)
+	$(call LINK,$@,$(OBJS))
+