diff --git a/.gitignore b/.gitignore
index ccd5e19..6ab7f77 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@ firmware/build/
 firmware/csr.json
 firmware/litex_json2dts_zephyr.py
 firmware/overlay.config
+firmware/overlay.cmake
 firmware/overlay.dts
 firmware/pin_io.h
 misc/
diff --git a/firmware/Makefile b/firmware/Makefile
index 895a3f9..167ceb1 100644
--- a/firmware/Makefile
+++ b/firmware/Makefile
@@ -2,7 +2,7 @@
 
 DEVICETREE_GEN_DIR=.
 
-all: rtl_codegen build/digilent_arty/digilent_arty.bit overlay.dts overlay.config pin_io.h
+all: rtl_codegen build/digilent_arty/digilent_arty.bit overlay.dts overlay.cmake pin_io.h
 
 rtl_codegen:
 	cd rtl && make
@@ -10,9 +10,9 @@ build/digilent_arty/digilent_arty.bit: rtl_codegen soc.py
 	python3 soc.py
 clean:
 	rm -rf build csr.json overlay.config overlay.dts pin_io.h
-overlay.dts overlay.config: csr.json litex_json2dts_zephyr.py
+overlay.dts overlay.cmake: csr.json litex_json2dts_zephyr.py
 	# NOTE: Broken in LiteX 2022.4.
-	$(DEVICETREE_GEN_DIR)/litex_json2dts_zephyr.py --dts overlay.dts --config overlay.config csr.json
+	$(DEVICETREE_GEN_DIR)/litex_json2dts_zephyr.py --dts overlay.dts --config overlay.cmake csr.json
 
 pin_io.h: csr.json generate_csr_locations.py
 	python3 generate_csr_locations.py > pin_io.h
diff --git a/software/CMakeLists.txt b/software/CMakeLists.txt
index ae3e92f..bead348 100644
--- a/software/CMakeLists.txt
+++ b/software/CMakeLists.txt
@@ -1,5 +1,11 @@
 cmake_minimum_required(VERSION 3.20.0)
 
+# These must come BEFORE the zephyr package declaration.
+set(DTC_OVERLAY_FILE "../firmware/overlay.dts")
+set(BOARD "litex_vexriscv")
+set(EXTRA_CFLAGS "-Wfatal-errors -Werror -Wno-error=unused-const-variable -Wno-error=unused-variable -Wno-error=unused-function")
+include("../firmware/overlay.cmake")
+
 find_package(Zephyr)
 project(upsilon)
 include_directories("../firmware")
@@ -7,4 +13,5 @@ include_directories("src/")
 include_directories("../creole")
 include_directories("../firmware/rtl/control_loop")
 
+# Add all source files here.
 target_sources(app PRIVATE src/access.c src/buf.c src/main.c src/sock.c ../creole/creole.c)
diff --git a/software/Makefile b/software/Makefile
index 98e1870..fc88d57 100644
--- a/software/Makefile
+++ b/software/Makefile
@@ -1,5 +1,12 @@
-build/zephyr/zephyr.bin: src/*.c ../firmware/overlay.dts ../firmware/pin_io.h
+unexport CXXFLAGS
+unexport CFLAGS
+unexport CPPFLAGS
+unexport LDFLAGS
+
+build/zephyr/zephyr.bin: build/Makefile
+	cd build && make -j7
+build/Makefile: ../creole/creole.c src/*.c ../firmware/overlay.dts ../firmware/pin_io.h
 	mkdir -p build
-	cd build && CMAKE_BINARY_DIR=$$(pwd) cmake $$(cat ../../firmware/overlay.config) -DDTC_OVERLAY_FILE=../firmware/overlay.dts -DBOARD=litex_vexriscv -DEXTRA_CFLAGS=-Wfatal-errors .. && make
+	cd build && cmake ..
 clean:
 	rm -rf build