-- asynchronous use of lpm_rom
-- this program reads the values in a rom using a counter as an address indicator. The 
-- data read appear one clock cycle behind the change of address, and a delay.

library IEEE;
use  IEEE.STD_LOGIC_1164.all;
use  IEEE.STD_LOGIC_ARITH.all;
use  IEEE.STD_LOGIC_UNSIGNED.all;
LIBRARY lpm;				-- required for the use of lpm functions 
USE lpm.lpm_components.ALL;

entity rom is
	generic (	rom_data_width : positive := 3;		-- width of data in rom
				rom_address_width : positive := 4;	-- width of address in rom
				rom_data_size : positive := 10);	-- number of values in rom
	PORT(	clock : in std_logic;			--system clock
			rom_data: out std_logic_vector(rom_data_width -1 downto 0)); 
			-- data in address indicated by "counter"
end rom;

architecture behavior of rom is
signal counter : std_logic_vector(rom_address_width -1 downto 0) := "0000"; -- address counter

begin 

	obtain_rom : lpm_rom
	GENERIC MAP (lpm_widthad => rom_address_width,	-- size of address of rom
        lpm_numwords => 10,		-- total number of values
        lpm_outdata => "UNREGISTERED",
        lpm_address_control => "UNREGISTERED",
        lpm_file => "primes.mif",	-- file to be read
        lpm_width => rom_data_width)				-- width of data
      PORT MAP ( address => counter, q => rom_data);

	address_count : process(clock) is
	begin
		if rising_edge(clock) then
			if counter = "1001" then
				counter <= (others => '0');	-- counter wraps at nine
			else
				counter <= counter + 1;
			end if;
		end if;
	end process;

end behavior;