diff --git a/firmware/rtl/testbench.hpp b/firmware/rtl/testbench.hpp
index 7976390..3f011c2 100644
--- a/firmware/rtl/testbench.hpp
+++ b/firmware/rtl/testbench.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#include <cstdint>
 #include <verilated.h>
+#include "util.hpp"
 
 /* https://zipcpu.com/blog/2017/06/21/looking-at-verilator.html */
 template <class TOP> class TB {
@@ -14,6 +14,7 @@ template <class TOP> class TB {
 	TB(int argc, char *argv[], int _bailout = 0) : mod(), bailout(_bailout), vc() {
 		vc.commandArgs(argc, argv);
 		vc.traceEverOn(true);
+
 		mod.clk = 0;
 		tick_count = 0;
 	}
@@ -22,10 +23,11 @@ template <class TOP> class TB {
 		mod.final();
 	}
 
-	virtual void run_clock() {
+	void run_clock() {
 		mod.clk = !mod.clk;
 		mod.eval();
 		vc.timeInc(1);
+
 		mod.clk = !mod.clk;
 		mod.eval();
 		vc.timeInc(1);
@@ -35,35 +37,3 @@ template <class TOP> class TB {
 			exit(1);
 	}
 };
-
-static inline void _assert(const char *file, int line, const char *exp, bool ev, const char *fmt, ...) {
-	if (!ev) {
-		va_list va;
-		va_start(va, fmt);
-		fprintf(stderr, "%s:%d: assertion failed: %s\n", file, line, exp);
-		vfprintf(stderr, fmt, va);
-		fprintf(stderr, "\n");
-		va_end(va);
-		exit(1);
-	}
-}
-#define STRINGIFY(s) #s
-/* ,##__VA_ARGS__ is a GNU C extension */
-#define my_assert(e, fmt, ...) _assert(__FILE__, __LINE__, STRINGIFY(e), (e), fmt ,##__VA_ARGS__)
-
-template<typename V>
-static inline V sign_extend(V x, unsigned len) {
-	/* if high bit is 1 */
-	if (x >> (len - 1) & 1) {
-		V mask = (1 << len) - 1;
-		return ~mask | x;
-	} else {
-		return x;
-	}
-}
-
-#define MASK(x,v) ((x) & ((1 << (v)) - 1))
-template<typename V>
-static inline V mask_extend(V x, unsigned len) {
-	return sign_extend<V>(MASK(x,len), len);
-}
diff --git a/firmware/rtl/util.hpp b/firmware/rtl/util.hpp
new file mode 100644
index 0000000..6733294
--- /dev/null
+++ b/firmware/rtl/util.hpp
@@ -0,0 +1,35 @@
+#pragma once
+#include <cstdio>
+
+static inline void _assert(const char *file, int line, const char *exp, bool ev, const char *fmt, ...) {
+	if (!ev) {
+		va_list va;
+		va_start(va, fmt);
+		fprintf(stderr, "%s:%d: assertion failed: %s\n", file, line, exp);
+		vfprintf(stderr, fmt, va);
+		fprintf(stderr, "\n");
+		va_end(va);
+		exit(1);
+	}
+}
+
+#define STRINGIFY(s) #s
+/* ,##__VA_ARGS__ is a GNU C extension */
+#define my_assert(e, fmt, ...) _assert(__FILE__, __LINE__, STRINGIFY(e), (e), fmt ,##__VA_ARGS__)
+
+template<typename V>
+static inline V sign_extend(V x, unsigned len) {
+	/* if high bit is 1 */
+	if (x >> (len - 1) & 1) {
+		V mask = (1 << len) - 1;
+		return ~mask | x;
+	} else {
+		return x;
+	}
+}
+
+#define MASK(x,v) ((x) & ((1 << (v)) - 1))
+template<typename V>
+static inline V mask_extend(V x, unsigned len) {
+	return sign_extend<V>(MASK(x,len), len);
+}