diff --git a/bench/servant_tb.cpp b/bench/servant_tb.cpp
index f779b23..6afaa19 100644
--- a/bench/servant_tb.cpp
+++ b/bench/servant_tb.cpp
@@ -117,12 +117,21 @@ int main(int argc, char **argv, char **env)
 	if (arg_timeout[0])
 	  timeout = atoi(arg_timeout+9);
 
+	vluint64_t vcd_start = 0;
+	const char *arg_vcd_start = Verilated::commandArgsPlusMatch("vcd_start=");
+	if (arg_vcd_start[0])
+	  vcd_start = atoi(arg_vcd_start+11);
+
+	bool dump = false;
 	top->wb_clk = 1;
 	bool q = top->q;
 	while (!(done || Verilated::gotFinish())) {
+	  if (tfp && !dump && (main_time > vcd_start)) {
+	    dump = true;
+	  }
 	  top->wb_rst = main_time < 100;
 	  top->eval();
-	  if (tfp)
+	  if (dump)
 	    tfp->dump(main_time);
 	  if (baud_rate)
 	    do_uart(&uart_context, top->q);
diff --git a/servant.core b/servant.core
index 5d55d3b..5f441f1 100644
--- a/servant.core
+++ b/servant.core
@@ -102,7 +102,15 @@ targets:
   verilator_tb:
     default_tool: verilator
     filesets : [soc, verilator_tb]
-    parameters : [RISCV_FORMAL, firmware, memsize, signature, timeout, uart_baudrate, vcd]
+    parameters :
+      - RISCV_FORMAL
+      - firmware
+      - memsize
+      - signature
+      - timeout
+      - uart_baudrate
+      - vcd
+      - vcd_start
     tools:
       verilator:
         verilator_options : [--trace]
@@ -155,6 +163,11 @@ parameters:
     datatype : bool
     paramtype : plusarg
 
+  vcd_start:
+    datatype    : int
+    description : Delay start of VCD dumping until the specified time
+    paramtype   : plusarg
+
 generate:
   icebreaker_pll:
     generator: icepll