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);

    Port0: inout std_logic_vector(7 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 := 15;

  constant R1END: integer := 1023+15;

  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);

  signal port0we: std_logic_vector(7 downto 0);

  signal port0temp: std_logic_vector(7 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

      datawrite <= x"0000";

      we <= "00";

    end if;

  end process;

  assignram: process (we, datawrite, addr, r1out, port0, WriteEnable, Address)

  variable tmp: integer;

  variable tmp2: integer;

  variable found: boolean := false;

  begin

    tmp := to_integer(unsigned(addr));

    tmp2 := to_integer(unsigned(Address));

    if tmp2 <= 15 then --internal registers/mapped IO

      if WriteWord='0' then

        if tmp2=0 then

          dataread <= x"0000";

          gen: for I in 0 to 7 loop

            if WriteEnable='1' then

              if port0we(I)='1' then --1-bit port set to WRITE mode

                port0(I) <= DataIn(I);

                port0temp(I) <= DataIn(I);

              else

                port0(I) <= 'Z';

              end if;

            else --not WE

              if port0we(I)='0' then --1-bit-port set to READ mode

                dataread(I) <= port0(I);

              else

                dataread(I) <= port0temp(I);

              end if;

            end if;

          end loop gen;

        elsif tmp2=1 then

          dataread <= x"00" & port0we;

          if WriteEnable='1' then

            port0we <= DataIn(7 downto 0);

            setwe: for I in 0 to 7 loop

              if DataIn(I)='0' then

                port0(I) <= 'Z';

              end if;

            end loop setwe;

          else

            dataread <= x"00" & port0we;

          end if;

        else

          --synthesis off

          report "Memory address is outside of bounds of RAM and registers" severity warning;

          --synthesis on

        end if;

      else

        --synthesis off

        report "WriteWord is not allowed in register area. Ignoring access" severity warning;

        --synthesis on

      end if;

    elsif tmp >= R1START and tmp <= R1END then --RAM bank1

      --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;