clkengenerator.vhd

ARM7核在FPGA中的VHDL代码实现

--****************************************************************************************************
-- Behavioural model of CLKEN generation for ARM core simualtion
-- Designed by Ruslan Lepetenok
-- Modified 01.01.2003
--****************************************************************************************************

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;

use Work.ARMSMSSPackage.all;
use WORK.ARMPackage.all;

entity CLKENGenerator is generic(SlowMemAdr : std_logic_vector(CSlowMemAdrWidth-1 downto 0);
								 NumberOfWS : positive
	                            );
	              port(
		     		   -- Global control signals
        			   nRESET  : in  std_logic;
					   CLK     : in  std_logic;
					   -- Memory request signals
					   TRANS   : in  std_logic_vector(1 downto 0);
					   -- ADDR and data
					   ADDR    : in  std_logic_vector(31 downto 0);
                       -- Output
					   CLKEN   : out std_logic
					   );
end CLKENGenerator;

architecture Beh of CLKENGenerator is

signal CLKEN_Int : std_logic := '0';

begin

CLKENGen:process(nRESET,CLK)
variable WSCnt : natural := 0;
begin
if nRESET='0' then                          -- Reset
 CLKEN_Int <= '1';
 WSCnt := 0;
  elsif CLK='1' and CLK'event then           -- Clock
   case CLKEN_Int is 
	when '1' =>
     if SlowMemAdr=ADDR(SlowMemAdr'range) and (TRANS=CTT_N or TRANS=CTT_S) then
      CLKEN_Int <= '0';	 	
	  WSCnt := NumberOfWS;
	 end if;

	 when '0' =>
	 if WSCnt=0 then
      CLKEN_Int <= '1';	 	
	 else 
	  WSCnt := WSCnt-1;
	 end if;
	
	when others => null;
   end case;	
	
end if;
end process;			

CLKEN <= CLKEN_Int;

end Beh;