
Build a 4-digit BCD (binary-coded decimal) counter. Each decimal digit is
encoded using 4 bits: q[3:0] is the ones digit, q[7:4] is the tens digit,
etc. For digits [3:1], also output an enable signal indicating when each
of the upper three digits should be incremented. Include a synchronous
active-high reset.

module TopModule (
  input clk,
  input reset,
  output [3:1] ena,
  output reg [15:0] q
);

