计数器vhdl代码

计数器vhdl代码。
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY ZBF_CHECK IS
PORT(clk,reset:IN STD_LOGIC;
     q:OUT STD_LOGIC_VECTOR(3 DOWNTO 0));
END ZBF_CHECK;
ARCHITECTURE struc OF ZBF_CHECK IS
SIGNAL q_temp:STD_LOGIC_VECTOR(3 DOWNTO 0);
BEGIN
PROCESS(clk)
BEGIN
IF(clk'EVENT AND clk='1')
THEN
  IF reset='1'
    THEN
    q_temp<="0000";
  ELSIF q_temp="1001"THEN
    q_temp<="0000";
    ELSE
    q_temp<=q_temp+1;
  END IF;
END IF;
END PROCESS;
q<=q_temp;
END struc;