diff --git a/.gitignore b/.gitignore
index 63e1e60..21b33ec 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,2 @@
-build/
+build/working/
 copy.sh
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..cfb31af
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "build"]
+	path = build
+	url = git@github.com:PxaMMaxP/Xilinx-ISE-Makefile.git
diff --git a/Makefile b/Makefile
deleted file mode 100644
index fab985a..0000000
--- a/Makefile
+++ /dev/null
@@ -1,243 +0,0 @@
-###########################################################################
-## Xilinx ISE Makefile
-##
-## To the extent possible under law, the author(s) have dedicated all copyright
-## and related and neighboring rights to this software to the public domain
-## worldwide. This software is distributed without any warranty.
-##
-## Makefile github repository: https://github.com/PxaMMaxP/Xilinx-ISE-Makefile
-###########################################################################
-
-###########################################################################
-# Version
-###########################################################################
-
-Makefile_Version := 1.0.1
-$(info ISE Makefile Version: $(Makefile_Version))
-
-###########################################################################
-# Include project configuration
-###########################################################################
-
-include project.cfg
-
-###########################################################################
-# Default values
-###########################################################################
-
-ifndef XILINX
-    $(error XILINX must be defined)
-endif
-
-ifndef PROJECT
-    $(error PROJECT must be defined)
-endif
-
-ifndef TARGET_PART
-    $(error TARGET_PART must be defined)
-endif
-
-TOPLEVEL         ?= $(PROJECT)
-CONSTRAINTS      ?= $(PROJECT).ucf
-BITFILE          ?= build/$(PROJECT).bit
- 
-COMMON_OPTS      ?= -intstyle xflow
-XST_OPTS         ?=
-NGDBUILD_OPTS    ?=
-MAP_OPTS         ?= -detail
-PAR_OPTS         ?=
-BITGEN_OPTS      ?=
-TRACE_OPTS       ?= -v 3 -n 3
-FUSE_OPTS        ?= -incremental
- 
-PROGRAMMER       ?= none
-PROGRAMMER_PRE   ?=
- 
-IMPACT_OPTS      ?= -batch impact.cmd
- 
-DJTG_EXE         ?= djtgcfg
-DJTG_DEVICE      ?= DJTG_DEVICE-NOT-SET
-DJTG_INDEX       ?= 0
-DJTG_FLASH_INDEX ?= 1
-
-XC3SPROG_EXE     ?= xc3sprog
-XC3SPROG_CABLE   ?= none
-XC3SPROG_OPTS    ?=
-
-
-###########################################################################
-# Internal variables, platform-specific definitions, and macros
-###########################################################################
-
-ifeq ($(OS),Windows_NT)
-    XILINX := $(shell cygpath -m $(XILINX))
-    CYG_XILINX := $(shell cygpath $(XILINX))
-    EXE := .exe
-    XILINX_PLATFORM ?= nt64
-    PATH := $(PATH):$(CYG_XILINX)/bin/$(XILINX_PLATFORM)
-else
-    EXE :=
-    XILINX_PLATFORM ?= lin64
-    PATH := $(PATH):$(XILINX)/bin/$(XILINX_PLATFORM)
-endif
-
-TEST_NAMES = $(foreach file,$(VTEST) $(VHDTEST),$(basename $(file)))
-TEST_EXES = $(foreach test,$(TEST_NAMES),build/isim_$(test)$(EXE))
-
-RUN = @echo "\n\e[1;33m============ $(1) ============\e[m\n"; \
-	cd build && $(XILINX)/bin/$(XILINX_PLATFORM)/$(1)
-
-# isim executables don't work without this
-export XILINX
-
-# Initialize the libs and paths variables for VHDL and Verilog sources
-VHD_PATHS ?=
-VHD_LIBS  ?=
-V_PATHS   ?=
-V_LIBS    ?=
-
-# Define a function to process source files
-define process_sources
-$(foreach src,$(1),\
-    $(eval lib_and_path=$(subst :, ,$(src))) \
-    $(eval libname=$(word 1,$(lib_and_path))) \
-    $(eval filepath=$(word 2,$(lib_and_path))) \
-    $(if $(filepath),,$(eval filepath=$(libname)) $(eval libname=work)) \
-    $(eval $(2) += $(libname)) \
-    $(eval $(3) += $(filepath)) \
-)
-endef
-
-# Run the function for VHDL sources
-$(eval $(call process_sources,$(VHDSOURCE),VHD_LIBS,VHD_PATHS))
-# Run the function for Verilog sources
-$(eval $(call process_sources,$(VSOURCE),V_LIBS,V_PATHS))
-
-###########################################################################
-# Default build
-###########################################################################
-
-default: $(BITFILE)
-
-clean:
-	rm -rf build
-
-build/$(PROJECT).prj: project.cfg
-	@echo "Updating $@"
-	@mkdir -p build
-	@rm -f $@
-	@$(foreach idx,$(shell seq 1 $(words $(V_PATHS))),echo "verilog $(word $(idx),$(V_LIBS)) \"../$(word $(idx),$(V_PATHS))\"" >> $@;)
-	@$(foreach idx,$(shell seq 1 $(words $(VHD_PATHS))),echo "vhdl $(word $(idx),$(VHD_LIBS)) \"../$(word $(idx),$(VHD_PATHS))\"" >> $@;)
-
-
-build/$(PROJECT)_sim.prj: build/$(PROJECT).prj
-	@cp build/$(PROJECT).prj $@
-	@$(foreach file,$(VTEST),echo "verilog work \"../$(file)\"" >> $@;)
-	@$(foreach file,$(VHDTEST),echo "vhdl work \"../$(file)\"" >> $@;)
-	@echo "verilog work $(XILINX)/verilog/src/glbl.v" >> $@
-
-build/$(PROJECT).scr: project.cfg
-	@echo "Updating $@"
-	@mkdir -p build
-	@rm -f $@
-	@echo "run" \
-	    "-ifn $(PROJECT).prj" \
-	    "-ofn $(PROJECT).ngc" \
-	    "-ifmt mixed" \
-	    "$(XST_OPTS)" \
-	    "-top $(TOPLEVEL)" \
-	    "-ofmt NGC" \
-	    "-p $(TARGET_PART)" \
-	    > build/$(PROJECT).scr
-
-$(BITFILE): project.cfg $(V_PATHS) $(VHD_PATHS) $(CONSTRAINTS) build/$(PROJECT).prj build/$(PROJECT).scr
-	@mkdir -p build
-	$(call RUN,xst) $(COMMON_OPTS) \
-	    -ifn $(PROJECT).scr
-	$(call RUN,ngdbuild) $(COMMON_OPTS) $(NGDBUILD_OPTS) \
-	    -p $(TARGET_PART) -uc ../$(CONSTRAINTS) \
-	    $(PROJECT).ngc $(PROJECT).ngd
-	$(call RUN,map) $(COMMON_OPTS) $(MAP_OPTS) \
-	    -p $(TARGET_PART) \
-	    -w $(PROJECT).ngd -o $(PROJECT).map.ncd $(PROJECT).pcf
-	$(call RUN,par) $(COMMON_OPTS) $(PAR_OPTS) \
-	    -w $(PROJECT).map.ncd $(PROJECT).ncd $(PROJECT).pcf
-	$(call RUN,bitgen) $(COMMON_OPTS) $(BITGEN_OPTS) \
-	    -w $(PROJECT).ncd $(PROJECT).bit
-	@echo "\e[1;32m============ OK ============\e[m\n\n"
-	@echo "\e[1;33m============ Reports.. ===========\e[m\n"
-	@echo "\e[1;97m==== Synthesis Summary Report ====\e[m"
-	@echo "\e[1;35m ./build/$(PROJECT).srp\e[m\n"
-	@echo "\e[1;97m======= Map Summary Report =======\e[m"
-	@echo "\e[1;35m ./build/$(PROJECT).map.mrp\e[m\n"
-	@echo "\e[1;97m======= PAR Summary Report =======\e[m"
-	@echo "\e[1;35m ./build/$(PROJECT).par\e[m\n"
-	@echo "\e[1;97m===== Pinout Summary Report ======\e[m"
-	@echo "\e[1;35m ./build/$(PROJECT)_pad.txt\e[m\n"
-	
-
-
-###########################################################################
-# Testing (work in progress)
-###########################################################################
-
-trace: project.cfg $(BITFILE)
-	$(call RUN,trce) $(COMMON_OPTS) $(TRACE_OPTS) \
-	    $(PROJECT).ncd $(PROJECT).pcf
-	@echo "\n\e[1;33m============ Reports.. ===========\e[m\n"
-	@echo "\e[1;97m===== Timing Summary Report ======\e[m"
-	@echo "\e[1;35m ./build/$(PROJECT).twr\e[m\n"
-
-test: $(TEST_EXES)
-
-build/isim_%$(EXE): $(V_PATHS) $(VHD_PATHS) build/$(PROJECT)_sim.prj $(VTEST) $(VHDTEST)
-	$(call RUN,fuse) $(COMMON_OPTS) $(FUSE_OPTS) \
-	    -prj $(PROJECT)_sim.prj \
-	    -o isim_$*$(EXE) \
-	    work.$* work.glbl
-
-isim: build/isim_$(TB)$(EXE)
-	@grep --no-filename --no-messages 'ISIM:' $(TB).{v,vhd} | cut -d: -f2 > build/isim_$(TB).cmd
-	@echo "run all" >> build/isim_$(TB).cmd
-	cd build ; ./isim_$(TB)$(EXE) -tclbatch isim_$(TB).cmd
-
-isimgui: build/isim_$(TB)$(EXE)
-	@grep --no-filename --no-messages 'ISIM:' $(TB).{v,vhd} | cut -d: -f2 > build/isim_$(TB).cmd
-	@echo "run all" >> build/isim_$(TB).cmd
-	cd build ; ./isim_$(TB)$(EXE) -gui -tclbatch isim_$(TB).cmd
-
-
-###########################################################################
-# Programming
-###########################################################################
-
-ifeq ($(PROGRAMMER), impact)
-prog: $(BITFILE)
-	$(PROGRAMMER_PRE) $(XILINX)/bin/$(XILINX_PLATFORM)/impact $(IMPACT_OPTS)
-endif
-
-ifeq ($(PROGRAMMER), digilent)
-prog: $(BITFILE)
-	$(PROGRAMMER_PRE) $(DJTG_EXE) prog -d $(DJTG_DEVICE) -i $(DJTG_INDEX) -f $(BITFILE)
-endif
-
-ifeq ($(PROGRAMMER), xc3sprog)
-prog: $(BITFILE)
-	$(PROGRAMMER_PRE) $(XC3SPROG_EXE) -c $(XC3SPROG_CABLE) $(XC3SPROG_OPTS) $(BITFILE)
-endif
-
-ifeq ($(PROGRAMMER), none)
-prog:
-	$(error PROGRAMMER must be set to use 'make prog')
-endif
-
-###########################################################################
-# Flash
-###########################################################################
-
-ifeq ($(PROGRAMMER), digilent)
-flash: $(BITFILE)
-	$(PROGRAMMER_PRE) $(DJTG_EXE) prog -d $(DJTG_DEVICE) -i $(DJTG_FLASH_INDEX) -f $(BITFILE)
-endif
-
-###########################################################################
diff --git a/build b/build
new file mode 160000
index 0000000..a8ed470
--- /dev/null
+++ b/build
@@ -0,0 +1 @@
+Subproject commit a8ed470e7de04ce923360ec480f3087795f136d6