diff --git a/npc/csrc/Flow/main.cpp b/npc/csrc/Flow/main.cpp
index 4728202..8a0f2ce 100644
--- a/npc/csrc/Flow/main.cpp
+++ b/npc/csrc/Flow/main.cpp
@@ -3,10 +3,30 @@
 #include <cstdlib>
 #include <verilated.h>
 #include <verilated_vcd_c.h>
+#include <VFlow.h>
+#define MAX_SIM_TIME 100
 
 int main(int argc, char **argv, char **env) {
     int sim_time = 0;
     Verilated::commandArgs(argc, argv);
 
+    VFlow *top = new VFlow;
+
+    Verilated::traceEverOn(true);
+    VerilatedVcdC *m_trace = new VerilatedVcdC; 
+#ifdef VERILATOR_TRACE
+    top->trace(m_trace, 5);
+    m_trace->open("waveform.vcd");
+#endif
+    for (sim_time = 0; sim_time < MAX_SIM_TIME; sim_time++) {
+        top->eval();
+#ifdef VERILATOR_TRACE
+        m_trace->dump(sim_time);
+#endif
+    }
+#ifdef VERILATOR_TRACE
+    m_trace->close();
+#endif
+    delete top;
     exit(EXIT_SUCCESS);
 }