library bv_utilities;

use bv_utilities.bv_arithmetic.bv_to_natural,
    bv_utilities.bv_arithmetic.natural_to_bv,
    std.textio.all;

architecture file_loaded of memory is
begin

  mem_behavior : process is

    constant high_address : natural := mem_size - 1;

    type memory_array is
      array (natural range 0 to high_address / 4) of dlx_bv_word;

    variable mem : memory_array;

    variable byte_address, word_address : natural;
    variable write_access : boolean;


    procedure load is

      file binary_file : text open read_mode is load_file_name;
      variable L : line;
      variable ch : character;
      variable line_number : natural := 0;
      variable addr : natural;
      variable word : dlx_bv_word;

      procedure read_hex_natural ( L : inout line;  n : out natural ) is
        variable result : natural := 0;
      begin
        for i in 1 to 8 loop
          read(L, ch);
          if '0' <= ch and ch <= '9' then
            result := result*16 + character'pos(ch) - character'pos('0');
          elsif 'A' <= ch and ch <= 'F' then
            result := result*16 + character'pos(ch) - character'pos('A') + 10;
          elsif 'a' <= ch and ch <= 'f' then
            result := result*16 + character'pos(ch) - character'pos('a') + 10;
          else
            report "Format error in file " & load_file_name
                   & " on line " & integer'image(line_number) severity error;
          end if;
        end loop;
        n := result;
      end read_hex_natural;

      procedure read_hex_word ( L : inout line;  word : out dlx_bv_word ) is
        variable digit : natural;
        variable r : natural := 0;
      begin
        for i in 1 to 8 loop
          read(L, ch);
          if '0' <= ch and ch <= '9' then
            digit := character'pos(ch) - character'pos('0');
          elsif 'A' <= ch and ch <= 'F' then
            digit := character'pos(ch) - character'pos('A') + 10;
          elsif 'a' <= ch and ch <= 'f' then
            digit := character'pos(ch) - character'pos('a') + 10;
          else
            report "Format error in file " & load_file_name
                   & " on line " & integer'image(line_number)
                   severity error;
          end if;
          word(r to r+3) := natural_to_bv(digit, 4);
          r := r + 4;
        end loop;
      end read_hex_word;

    begin
      while not endfile(binary_file) loop
        readline(binary_file, L);
        line_number := line_number + 1;
        read_hex_natural(L, addr);
        read(L, ch);  -- the space between addr and data
        read_hex_word(L, word);
        mem(addr / 4) := word;
      end loop;
    end load;

    procedure do_write is
      subtype ls_2_bits is bit_vector(1 downto 0);
    begin
      case width is
        when dlx_mem_width_word =>
          mem(word_address) := to_bitvector(d);
        when dlx_mem_width_halfword =>
          if To_bit(a(1)) = '0' then  -- ms half word
            mem(word_address)(0 to 15) := to_bitvector( d(0 to 15) );
          else  -- ls half word
            mem(word_address)(16 to 31) := to_bitvector( d(16 to 31) );
          end if;
        when dlx_mem_width_byte =>
          case ls_2_bits'(To_bitvector(a(1 downto 0))) is
            when b"00" =>
              mem(word_address)(0 to 7) := to_bitvector( d(0 to 7) );
            when b"01" =>
              mem(word_address)(8 to 15) := to_bitvector( d(8 to 15) );
            when b"10" =>
              mem(word_address)(16 to 23) := to_bitvector( d(16 to 23) );
            when b"11" =>
              mem(word_address)(24 to 31) := to_bitvector( d(24 to 31) );
          end case;
        when others =>
          report "illegal width indicator in write" severity error;
      end case;
    end do_write;

    procedure do_read is
    begin
      d <= To_X01( mem(word_address) );
    end do_read;


  begin
    load;  -- read binary memory image into memory array
    -- initialize outputs
    d <= disabled_dlx_word;
    ready <= '0';

    -- process memory cycles
    loop
      -- wait for a command, valid on leading edge of phi2
      wait on phi2 until rising_edge(phi2) and To_bit(mem_enable) = '1';

      -- decode address and perform command if selected
      byte_address := bv_to_natural(To_bitvector(a));
      write_access := To_bit(write_enable) = '1';
      if byte_address <= high_address then
        word_address := byte_address / 4;
        if write_access then -- write cycle
          do_write;
          wait for Tac_first;  -- write access time, 1st cycle
        else -- read cycle
          wait for Tac_first;  -- read access time, 1st cycle
          do_read;
        end if;
        -- ready synchronous with phi2
        wait until rising_edge(phi2);
        ready <= '1' after Tpd_clk_out;
        wait until falling_edge(phi2);
        ready <= '0' after Tpd_clk_out;
        --  do subsequent cycles in burst
        while To_bit(burst) = '1' loop
          word_address := (word_address + 1) mod (mem_size / 4);
          wait until rising_edge(phi2);
          if write_access then -- write cycle
            do_write;
            wait for Tac_burst;  -- write access time, burst cycle
          else -- read cycle
            wait for Tac_burst;  -- read access time, burst cycle
            do_read;
          end if;
          -- ready synchronous with phi2
          wait until rising_edge(phi2);
          ready <= '1' after Tpd_clk_out;
          wait until falling_edge(phi2);
          ready <= '0' after Tpd_clk_out;
        end loop;
        if not write_access then  -- was read
          d <= disabled_dlx_word after Tpd_clk_out;
        end if;
      end if;
    end loop;
  end process mem_behavior;

end architecture file_loaded;

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