module bit_error_rate(in,ref);
 input in,ref;
 voltage in,reg;

 parameter real period=1 from [0:inf),
                vth=2.5;

 integer bits,errors;

 analog
 begin
   @(initial_step)
   begin
     bits = 0;
     errors = 0;
   end

   @(timer(0,period))
   begin
     if ((V(in) > vth) != (V(ref) > vth))
       errors = errors+1;
     bits = bits+1;
   end

   @(final_step)
     $strobe("bit error rate = %f%%", 100*errors/bits);
 end
endmodule