diff --git a/CMakeLists.txt b/CMakeLists.txt
index 475dbc7..49e6bdd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,10 @@ set(CMAKE_CXX_STANDARD 20)
 
 include_directories(include)
 
-add_executable(simulator ${sources})
+# add_executable(simulator ${sources})
 
 add_executable(alu demo/alu.cpp)
+
+# For debug build
+add_executable(modules demo/modules.cpp)
+target_compile_definitions(modules PRIVATE _DEBUG)
diff --git a/demo/modules.cpp b/demo/modules.cpp
new file mode 100644
index 0000000..d07b085
--- /dev/null
+++ b/demo/modules.cpp
@@ -0,0 +1,101 @@
+#include "tools.h"
+#include <iostream>
+
+struct RegFile_Input {
+	Wire <5> rs1_index;		// Read
+	Wire <5> rs2_index;		// Read
+
+	Wire <5> wb_index;		// Writeback
+	Wire <1> wb_enable;		// Writeback enabled?
+	Wire <32> wb_data;		// Data to writeback
+};
+
+struct RegFile_Output {
+	Register <32> rs1_data;		// Read
+	Register <32> rs2_data;		// Read
+};
+
+struct RegFile_Private {
+	std::array <Register<32>, 32> regs;
+};
+
+struct RegFile : dark::Module <RegFile_Input, RegFile_Output, RegFile_Private> {
+	void work() override final {
+		rs1_data <= regs[to_unsigned(rs1_index)];
+		rs2_data <= regs[to_unsigned(rs2_index)];
+
+		if (wb_enable && wb_index != 0) {
+			regs[to_unsigned(wb_index)] <= wb_data;
+		}
+
+	}
+};
+
+struct InsDecode_Input {
+	Wire <32> rs1_data;
+	Wire <32> rs2_data;
+};
+
+struct InsDecode_Output {
+	Register <5> rs1_index;
+	Register <5> rs2_index;
+	Register <5> wb_index;
+	Register <32> wb_data;
+	Register <1> wb_enable;
+};
+
+struct InsDecode : dark::Module <InsDecode_Input, InsDecode_Output> {
+	void work() override final {
+		char c;
+		max_size_t x;
+		max_size_t y;
+		std::cin >> c >> x >> y;
+		if (c == 'r') {
+			rs1_index <= x;
+			rs2_index <= y;
+			wb_index <= 0;
+			wb_data <= 0;
+			wb_enable <= 0;
+		} else {
+			rs1_index <= 0;
+			rs2_index <= 0;
+			wb_index <= x;
+			wb_data <= y;
+			wb_enable <= 1;
+		}
+
+		std::cout << "rs1_data: " << to_unsigned(rs1_data) << std::endl;
+		std::cout << "rs2_data: " << to_unsigned(rs2_data) << std::endl;
+	}
+};
+
+signed main() {
+	InsDecode ins_decode;
+	RegFile reg_file;
+
+	dark::CPU cpu;
+
+	cpu.add_module(&ins_decode);
+	cpu.add_module(&reg_file);
+
+	reg_file.rs1_index = [&]() -> auto & { return ins_decode.rs1_index; };
+	reg_file.rs2_index = [&]() -> auto & { return ins_decode.rs2_index; };
+	reg_file.wb_index = [&]() -> auto & { return ins_decode.wb_index; };
+	reg_file.wb_enable = [&]() -> auto & { return ins_decode.wb_enable; };
+	reg_file.wb_data = [&]() -> auto & { return ins_decode.wb_data; };
+
+	ins_decode.rs1_data = [&]() -> auto & { return reg_file.rs1_data; };
+	ins_decode.rs2_data = [&]() -> auto & { return reg_file.rs2_data; };
+
+	cpu.run(114514, true);
+
+	// Demo input:
+	// w 1 2	(output 0 0)
+	// r 1 2	(output 0 0)
+	// w 2 3	(output 0 0)
+	// r 1 2	(output 2 0)
+	// r 1 2	(output 0 0)
+	// r 1 2	(output 2 3)
+
+	return 0;
+}