diff --git a/main_tb.sv b/main_tb.sv
index 56e9eb9..7486917 100644
--- a/main_tb.sv
+++ b/main_tb.sv
@@ -21,11 +21,17 @@ initial begin
 end
 
 // external device "asynchronous" clock
-logic clk33;
+logic clk33a;
 initial begin
-  #0 clk33 = 1'b0;
+  #0 clk33a = 1'b0;
   forever
-    #15.151 clk33 = ~clk33;
+    #7 clk33a = ~clk33a;
+end
+
+logic clk33;
+//assign clk33 = clk33a;
+always @(*) begin
+  clk33 = #($urandom_range(0, 2000)*10ps) clk33a;
 end
 
 logic rst;