diff --git a/npc/csrc/main.cpp b/npc/csrc/main.cpp
index 0965795..70e48e4 100644
--- a/npc/csrc/main.cpp
+++ b/npc/csrc/main.cpp
@@ -5,8 +5,10 @@
 #include <verilated_vcd_c.h>
 #include "Vexample.h"
 
+#define MAX_SIM_TIME 100
+
 int main(int argc, char **argv, char **env) {
-    int round = 100;
+    int sim_time = 0;
     Verilated::commandArgs(argc, argv);
     Vexample *top = new Vexample;
 
@@ -14,7 +16,7 @@ int main(int argc, char **argv, char **env) {
     VerilatedVcdC *m_trace = new VerilatedVcdC; 
     top->trace(m_trace, 5);
     m_trace->open("waveform.vcd");
-    while (round--) {
+    for (sim_time = 0; sim_time < MAX_SIM_TIME; sim_time++) {
         int a = rand() & 1;
         int b = rand() & 1;
         top->a = a;
@@ -22,6 +24,7 @@ int main(int argc, char **argv, char **env) {
         top->eval();
         printf("a = %d, b = %d, f = %d\n", a, b, top->f);
         assert(top->f == (a ^ b));
+        m_trace->dump(sim_time);
     }
     m_trace->close();
     delete top;