// tail.v   tail, right, left, osc, right_light, left_light

`timescale 1ns/1ns // set time unit and time lsb
// `include "tail_lights.v"

module tail_lights(tail, right, left, osc, right_light, left_light);
  input  tail;
  input  right;
  input  left;
  input  osc;
  output right_light;  
  output left_light;  
  assign #1 right_light = (tail&~right)|(right&osc);
  assign #1 left_light = (osc&left)|(~left&tail);
endmodule // tail_lights

module tail;
  reg tail, right, left, osc;
  wire right_light, left_light;
  tail_lights tl(tail, right, left, osc, right_light, left_light);
   
  initial
    begin
      tail = 0;
      right = 0;
      left = 0;
      osc = 1; // should be 1010101010 ...
    end

  always
    begin       
      #2 $display("tail=%b, right=%b, left=%b, osc=%b, right_light=%b, left_light=%b",
               tail, right, left, osc, right_light, left_light);
      #3tail = 1;
      #4 $display("tail=%b, right=%b, left=%b, osc=%b, right_light=%b, left_light=%b",
               tail, right, left, osc, right_light, left_light);
      #5tail = 0;
      #5right = 1;
      #6 $display("tail=%b, right=%b, left=%b, osc=%b, right_light=%b, left_light=%b",
               tail, right, left, osc, right_light, left_light);

      #7right = 0;
      #7left = 1;
      #8 $display("tail=%b, right=%b, left=%b, osc=%b, right_light=%b, left_light=%b",
               tail, right, left, osc, right_light, left_light);
      
      $finish; 
    end
endmodule