   @doc """
   Stop the UART GenServer.
   """
+  @spec stop(pid) :: :ok
   def stop(pid) do
     GenServer.stop(pid)
   end

  @doc """
  Write data to the opened UART with the default timeout.
  """
  def write(pid, data) do
    write(pid, data, 5000)
  end

  @doc """
  Start up a UART GenServer.
  """
  @spec start_link([keyword]) :: {:ok, pid} | {:error, term}
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, [], opts)
  end
