index_counter.vhd

--------------------------------------------------------------------------

-- FILENAME : index_counter.vhd

--

-- Count the number of INDEX pulses (the number of disk revolutions).  The

-- output is used as a timeout when searching for a particular sector.

--

-- AUTHOR       : Craig Dunn

-- DATE STARTED : 30 December 2003

-- TAB SETTING  : 4

-- RESET        : None

-- CLOCK        : INDEX

-- KNOWN BUGS   : None

-- VERSION      : 1.0

--

-- All of the design and code in this module is my own work.  No design or

-- code has been borrowed or copied from any source.

--------------------------------------------------------------------------

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;



entity index_counter is

    Port ( INDEX     : in std_logic;

           COUNT     : out std_logic_vector(3 downto 0)

         );

end index_counter;



architecture index_counter_arch of index_counter is

   signal sig_count : std_logic_vector(3 downto 0);

begin



   COUNT <= sig_count;



   main : process(INDEX)

   begin

      if rising_edge(INDEX) then

         if sig_count < "1111" then

            sig_count <= sig_count + '1';

         else

            sig_count <= (others => '0');

         end if;

      end if;

   end process main;



end index_counter_arch;