11.2.1.1.7 Rising Edge Flip-Flop with Asynchronous Reset and Clock Enable

library IEEE;
use IEEE.std_logic_1164.all;
entity dff_ck_en is
port (data, clk, reset, en : in std_logic;
q : out std_logic);
end dff_ck_en;
architecture behav of dff_ck_en is
begin
process (clk, reset) begin
if (reset = '0') then
q <= '0';
elsif (clk'event and clk = '1') then
if (en = '1') then
q <= data;
end if;
end if;
end process;
end behav;

module dff_ck_en (data, clk, reset, en, q);
input data, clk, reset, en;
output q;
reg q;
always @ (posedge clk or negedge reset)
if (~reset)
q = 1'b0;
else if (en)
q = data;
endmodule