makefiles: add atmega arch generic makefile

makefiles/arch/atmega.inc.mk

@@ -0,0 +1,50 @@
+# Target architecture for the build. Use avr if you are unsure.
+TARGET_ARCH ?= avr
+
+CFLAGS_CPU   = -mmcu=$(CPU) $(CFLAGS_FPU)
+CFLAGS_LINK  = -ffunction-sections -fdata-sections -fno-builtin -fshort-enums
+CFLAGS_DBG  ?= -ggdb -g3
+CFLAGS_OPT  ?= -Os
+
+CFLAGS    += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_DBG) $(CFLAGS_OPT)
+ASFLAGS   += $(CFLAGS_CPU) $(CFLAGS_DBG)
+LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT) -static -lgcc -e reset_handler -Wl,--gc-sections
+OFLAGS    += -j .text -j .data
+
+# Tell the build system that the CPU depends on the atmega common files:
+USEMODULE += atmega_common
+
+# export the peripheral drivers to be linked into the final binary
+USEMODULE += atmega_common_periph
+USEMODULE += periph_common
+
+# Export the peripheral drivers to be linked into the final binary, for now
+# only atmega126rfr2 has periph drivers
+ifeq ($(CPU), atmega256rfr2)
+  USEMODULE += periph
+endif
+
+# the atmel port uses stdio_uart
+USEMODULE += stdio_uart
+
+# explicitly tell the linker to link the syscalls and startup code.
+# without this the interrupt vectors will not be linked correctly!
+UNDEF += $(BINDIR)/atmega_common/startup.o
+
+# Use ROM_LEN and RAM_LEN during link
+$(if $(ROM_LEN),,$(error ROM_LEN is not defined))
+$(if $(RAM_LEN),,$(error RAM_LEN is not defined))
+LINKFLAGS += $(LINKFLAGPREFIX)--defsym=__TEXT_REGION_LENGTH__=$(ROM_LEN)$(if $(ROM_RESERVED),-$(ROM_RESERVED))
+LINKFLAGS += $(LINKFLAGPREFIX)--defsym=__DATA_REGION_LENGTH__=$(RAM_LEN)
+
+# Use newer linker script to have ROM/RAM configuration symbols in binutils<2.26
+LDSCRIPT_COMPAT = $(if $(shell $(TARGET_ARCH)-ld --verbose | grep __TEXT_REGION_LENGTH__),,\
+                    -T$(RIOTCPU)/$(CPU)/ldscripts_compat/avr_2.26.ld)
+LINKFLAGS += $(LDSCRIPT_COMPAT)
+
+ifeq ($(LTO),1)
+  # avr-gcc <4.8.3 has a bug when using LTO which causes a warning to be printed always:
+  # '_vector_25' appears to be a misspelled signal handler [enabled by default]
+  # See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59396
+  LINKFLAGS += -Wno-error
+endif