atusb/fw/Makefile: introduce target-specific compliation variants

- Makefile (USB_OBJS): moved into OBJS and BOOT_OBJS
- Makefile (OBJS): atu2.o is now app-atu2.o
- Makefile (BOOT_OBJS): atu2.o is now boot-atu2.o
- Makefile (MKDEP, %.o): moved dependency generation to macro $(MKDEP)
- Makefile (app-%.o): build from usb/%.c
- Makefile (boot -%.o): build from usb/%.c and set -DBOOT_LOADER

atusb/fw/Makefile

@@ -30,11 +30,10 @@ SIZE = $(AVR_PREFIX)size
 
 USB_ID = 20b7:1540
 
-USB_OBJS = usb.o atu2.o
+OBJS = atusb.o board.o board_app.o sernum.o spi.o descr.o ep0.o \
-OBJS = atusb.o board.o board_app.o sernum.o spi.o descr.o ep0.o dfu_common.o \
+       dfu_common.o usb.o app-atu2.o
-       $(USB_OBJS)
+BOOT_OBJS = boot.o board.o sernum.o spi.o flash.o dfu.o \
-BOOT_OBJS = boot.o board.o sernum.o spi.o flash.o dfu.o dfu_common.o \
+            dfu_common.o usb.o boot-atu2.o
-	    $(USB_OBJS)
 
 vpath %.c usb/
 
@@ -110,16 +109,32 @@ version.c:
 
 # ----- Dependencies ----------------------------------------------------------
 
+MKDEP =									\
+	$(DEPEND) $< |							\
+	  sed 								\
+	    -e 's|^$(basename $(notdir $<)).o:|$@:|'			\
+	    -e '/^\(.*:\)\? */{p;s///;s/ *\\\?$$/ /;s/  */:\n/g;H;}'	\
+	    -e '$${g;p;}'						\
+	    -e d >$(basename $@).d;					\
+	  [ "$${PIPESTATUS[*]}" = "0 0" ] ||				\
+	  { rm -f $(basename $@).d; exit 1; }
+
 %.o:            %.c
 		$(CC) $(CFLAGS) -Os -c $<
-		$(DEPEND) $< | \
+		$(MKDEP)
-		  sed -e \
-		    '/^\(.*:\)\? */{p;s///;s/ *\\\?$$/ /;s/  */:\n/g;H;}' \
-		    -e '$${g;p;}' -e d >$*.d; \
-		  [ "$${PIPESTATUS[*]}" = "0 0" ] || { rm -f $*.d; exit 1; }
 
 -include $(OBJS:.o=.d)
 
+# ----- Object file variants --------------------------------------------------
+
+app-%.o:	usb/%.c
+		$(CC) $(CFLAGS) -Os -o $@ -c $<
+		$(MKDEP)
+
+boot-%.o:	usb/%.c
+		$(CC) $(CFLAGS) -DBOOT_LOADER -Os -o $@ -c $<
+		$(MKDEP)
+
 # ----- Programming and device control ----------------------------------------
 
 upload:		$(NAME).bin boot.hex