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-- Copyright (c)2013, 2020 Jeremy Seth Henry

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-- VHDL Units :  o8_ram_1k

-- Description:  Provides a wrapper layer for a 1kx8 RAM model

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      04/16/20 Revision block added

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

library work;

  use work.open8_pkg.all;

entity o8_ram_4k is

generic(

  Address                    : ADDRESS_TYPE

);

port(

  Open8_Bus                  : in  OPEN8_BUS_TYPE;

  Rd_Data                    : out DATA_TYPE

);

end entity;

architecture behave of o8_ram_4k is

  alias Clock                is Open8_Bus.Clock;

  alias Reset                is Open8_Bus.Reset;

  constant User_Addr         : std_logic_vector(15 downto 12)

                               := Address(15 downto 12);

  alias Comp_Addr            is Open8_Bus.Address(15 downto 12);

  alias RAM_Addr             is Open8_Bus.Address(11 downto 0);

  signal Addr_Match          : std_logic := '0';

  signal Wr_En               : std_logic := '0';

  signal Rd_En               : std_logic := '0';

  signal Rd_Data_i           : DATA_TYPE := OPEN8_NULLBUS;

begin

  -- This decode needs to happen immediately, to give the RAM a chance to

  --  do the lookup before we have to set Rd_Data

  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';

  Wr_En                      <= Addr_Match and Open8_Bus.Wr_En;

  -- Note that this RAM should be created without an output FF (unregistered Q)

  U_RAM : entity work.ram_4k_core

  port map(

    address                  => RAM_Addr,

    clock                    => Clock,

    data                     => Open8_Bus.Wr_Data,

    wren                     => Wr_En,

    q                        => Rd_Data_i

  );

  RAM_proc: process( Reset, Clock )

  begin

    if( Reset = Reset_Level )then

      Rd_En                  <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

    elsif( rising_edge(Clock) )then

      Rd_En                  <= Addr_Match and Open8_Bus.Rd_En;

      Rd_Data                <= OPEN8_NULLBUS;

      if( Rd_En = '1' )then

        Rd_Data              <= Rd_Data_i;

      end if;

    end if;

  end process;

end architecture;