makefiles/blob.inc.mk: introduce blob -> hdr utility makefile

Makefile.base

@@ -75,6 +75,8 @@ ASSMOBJ     := $(ASSMSRC:%.S=$(BINDIR)/$(MODULE)/%.o)
 OBJ := $(OBJC) $(OBJCXX) $(ASMOBJ) $(ASSMOBJ) $(GENOBJC)
 DEP := $(OBJC:.o=.d) $(OBJCXX:.o=.d) $(ASSMOBJ:.o=.d)
 
+include $(RIOTMAKE)/blob.inc.mk
+
 $(BINDIR)/$(MODULE)/:
 	$(Q)mkdir -p $@
 

makefiles/blob.inc.mk

@@ -0,0 +1,65 @@
+#
+# makes any file in BLOBS available via '#include "blob/<filename>.h"
+#
+# # Usage:
+#
+# Add this to an application or module Makefile:
+#
+#     BLOBS += foo.ext
+#
+# Then include in C file or header:
+#
+#    #include "blob/foo.ext.h"
+#
+# The blob can then be accessed using the symbols "foo_ext" and "foo_ext_len".
+#
+# # Subfolders
+#
+# It is possible to add files from subfolders to BLOBS:
+#
+#     BLOBS += subfolder/my_file.foo
+#
+# The subfolder will be part of the generated header's path, but *not* of the
+# generated symbols. E.g., above blob would be made available by including
+# "blobs/subfolder/my_file.ext.h", which would define the symbols "my_file_ext"
+# and "my_file_ext_len". Beware possible symbol name clashes.
+#
+
+# use "blobs/blob" so the headers can be included as "blob/foo.h", but
+# we don't have to add $(BINDIR)/$(MODULE) to the include path.
+BLOB_HDR_DIR ?= $(BINDIR)/$(MODULE)/blobs/blob
+BLOB_H := $(BLOBS:%=$(BLOB_HDR_DIR)/%.h)
+
+ifneq (, $(BLOB_H))
+  # add $(BINDIR)/$(MODULE)/blobs to include path
+  CFLAGS += -I$(dir $(BLOB_HDR_DIR))
+endif
+
+# In order to allow automatic folder creation in subtrees,
+# this Makefile makes use SECONDEXPANSION, PRECIOUS and
+# order only prerequisites.
+# Folder targets are "tagged" by appending "/."
+# The final recipe uses "| $$(@D)/." to create necessary trees.
+#
+# Inspiration from:
+# http://ismail.badawi.io/blog/2017/03/28/automatic-directory-creation-in-make/
+#
+.PRECIOUS: $(BLOB_HDR_DIR)/. $(BLOB_HDR_DIR)%/.
+
+$(BLOB_HDR_DIR)/.:
+	@mkdir -p $@
+
+$(BLOB_HDR_DIR)%/.:
+	@mkdir -p $@
+
+XXD ?= xxd
+
+$(BLOB_H): $(BLOB_HDR_DIR)/%.h: % $(BLOBS) | $$(@D)/.
+	@command -v $(XXD) > /dev/null 2>&1 || ( \
+	  echo "error: xxd binary '$(XXD)' not found! (Maybe install vim package?)"; exit 1)
+
+	${Q}cd $(dir $<); xxd -i $(notdir $<) | sed 's/^unsigned/const unsigned/g'> $@
+
+# make C and C++ objects of this module depend on generated headers, so they
+# get re-build on changes to the blob files.
+$(OBJC) $(OBJCXX): $(BLOB_H)