Subversion Repositories tinycpu

--Memory management component

--By having this separate, it should be fairly easy to add RAMs or ROMs later

--This basically lets the CPU not have to worry about how memory "Really" works

--currently just one RAM. 1024 byte blockram.vhd mapped as 0 - 1023

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.NUMERIC_STD.ALL;

entity memory is

  port(

    Address: in std_logic_vector(15 downto 0); --memory address (in bytes)

    WriteWord: in std_logic; --if set, will write a full 16-bit word instead of a byte. Address must be aligned to 16-bit address. (bottom bit must be 0)

    WriteEnable: in std_logic;

    Clock: in std_logic;

    DataIn: in std_logic_vector(15 downto 0);

    DataOut: out std_logic_vector(15 downto 0)

--    Reset: in std_logic

    --RAM/ROM interface (RAMA is built in to here

    --RAMBDataIn: out std_logic_vector(15 downto 0);

    --RAMBDataOut: in std_logic_vector(15 downto 0);

    --RAMBAddress: out std_logic_vector(15 downto 0);

    --RAMBWriteEnable: out std_logic_vector(1 downto 0);

  );

end memory;

architecture Behavioral of memory is

  component blockram

    port(

      Address: in std_logic_vector(7 downto 0); --memory address

      WriteEnable: in std_logic_vector(1 downto 0); --write or read

      Enable: in std_logic;

      Clock: in std_logic;

      DataIn: in std_logic_vector(15 downto 0);

      DataOut: out std_logic_vector(15 downto 0)

    );

  end component;

  constant R1START: integer := 0;

  constant R1END: integer := 1023;

  signal addr: std_logic_vector(15 downto 0) := (others => '0');

  signal R1addr: std_logic_vector(7 downto 0);

  signal we: std_logic_vector(1 downto 0);

  signal datawrite: std_logic_vector(15 downto 0);

  signal dataread: std_logic_vector(15 downto 0);

  --signal en: std_logic;

  signal R1we: std_logic_vector(1 downto 0);

  signal R1en: std_logic;

  signal R1in: std_logic_vector(15 downto 0);

  signal R1out: std_logic_vector(15 downto 0);

begin

  R1: blockram port map (R1addr, R1we, R1en, Clock, R1in, R1out);

  addrwe: process(Address, WriteWord, WriteEnable, DataIn)

  begin

    addr <= Address(15 downto 1) & '0';

    if WriteEnable='1' then

      if WriteWord='1' then

        we <= "11";

        datawrite <= DataIn;

      else

        if Address(0)='0' then

          we <= "01";

          datawrite <= x"00" & DataIn(7 downto 0); --not really necessary

        else

          we <= "10";

          datawrite <= DataIn(7 downto 0) & x"00";

        end if;

      end if;

    else

      we <= "00";

    end if;

  end process;

  assignram: process (we, datawrite, addr, r1out)

  variable tmp: integer;

  variable found: boolean := false;

  begin

    tmp := to_integer(unsigned(addr));

    if tmp >= R1START and tmp <= R1END then

      --map all to R1

      found := true;

      R1en <= '1';

      R1we <= we;

      R1in <= datawrite;

      dataread <= R1out;

      R1addr <= addr(8 downto 1);

    else

      R1en <= '0';

      R1we <= "00";

      R1in <= x"0000";

      R1addr <= x"00";

      dataread <= x"0000";

    end if;

  end process;

  readdata: process(Address, dataread)

  begin

    if Address(0) = '0' then

      DataOut <= dataread;

    else

      DataOut <= x"00" & dataread(15 downto 8);

    end if;

  end process;

end Behavioral;