programmable parallel to serial converter

I try write a draft of code sample.

entity P2S is
    port ( Serial_out : out std_logic;
    clk : in std_logic;
    Parallel_data : in std_logic_vector(15 downto 0);
    Data_length : in std_logic_vector(3 downto 0);
    DataReady : in std_logic);
end P2S;
architecture Behavioral of P2S is
  signal temp : std_logic_vector(15 downto 0);
  signal counter: integer;
  begin
      process(rst, clk)
         begin
                if(clk='1' and clk'event) then
                     if (DataReady) then 
                           counter<=0;
 	        elsif (counter<Data_length) then
		   Serial_out<=Parallel_data(counter);
                           counter<=counter+1;
                    else
		Serial_out<='0':
                   end if;
              end if; 
       end process;
end Behavioral;