Subversion Repositories neo430

-- #################################################################################################

-- #  << NEO430 - Instruction memory ("IMEM") >>                                                   #

-- # ********************************************************************************************* #

-- # This memory includes the in-place executable image of the application. See the                #

-- # processor's documentary to get more information.                                              #

-- # Note: IMEM is split up into two 8-bit memories - some EDA tools have problems to synthesize   #

-- # a pre-initialized 16-bit memory with byte-enable signals.                                     #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #

-- #                                                                                               #

-- # Redistribution and use in source and binary forms, with or without modification, are          #

-- # permitted provided that the following conditions are met:                                     #

-- #                                                                                               #

-- # 1. Redistributions of source code must retain the above copyright notice, this list of        #

-- #    conditions and the following disclaimer.                                                   #

-- #                                                                                               #

-- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of     #

-- #    conditions and the following disclaimer in the documentation and/or other materials        #

-- #    provided with the distribution.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS   #

-- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF               #

-- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE    #

-- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,     #

-- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #

-- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED    #

-- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING     #

-- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED  #

-- # OF THE POSSIBILITY OF SUCH DAMAGE.                                                            #

-- # ********************************************************************************************* #

-- # The NEO430 Processor - https://github.com/stnolting/neo430                                    #

-- #################################################################################################

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neo430;

use neo430.neo430_package.all;

use neo430.neo430_application_image.all; -- this file is generated by the image generator

entity neo430_imem is

  generic (

    IMEM_SIZE   : natural := 4*1024; -- internal IMEM size in bytes

    IMEM_AS_ROM : boolean := false;  -- implement IMEM as read-only memory?

    BOOTLD_USE  : boolean := true    -- implement and use bootloader?

  );

  port (

    clk_i  : in  std_ulogic; -- global clock line

    rden_i : in  std_ulogic; -- read enable

    wren_i : in  std_ulogic_vector(01 downto 0); -- write enable

    upen_i : in  std_ulogic; -- update enable

    addr_i : in  std_ulogic_vector(15 downto 0); -- address

    data_i : in  std_ulogic_vector(15 downto 0); -- data in

    data_o : out std_ulogic_vector(15 downto 0)  -- data out

  );

end neo430_imem;

architecture neo430_imem_rtl of neo430_imem is

  -- ROM types --

  type imem_file8_t is array (0 to IMEM_SIZE/2-1) of std_ulogic_vector(07 downto 0);

  -- init function and split 1x16-bit memory into 2x8-bit memories --

  impure function init_imem(hilo : std_ulogic; init : application_init_image_t) return imem_file8_t is

    variable mem_v : imem_file8_t;

  begin

    for i in 0 to IMEM_SIZE/2-1 loop

      if (hilo = '0') then -- low byte

        mem_v(i) := init(i)(07 downto 00);

      else -- high byte

        mem_v(i) := init(i)(15 downto 08);

      end if;

    end loop; -- i

    return mem_v;

  end function init_imem;

  -- local signals --

  signal acc_en : std_ulogic;

  signal rdata  : std_ulogic_vector(15 downto 0);

  signal rden   : std_ulogic;

  signal addr   : integer;

  -- internal "RAM" type - implemented if bootloader is used and IMEM is RAM and initialized with app code --

  signal imem_file_init_ram_l : imem_file8_t := init_imem('0', application_init_image);

  signal imem_file_init_ram_h : imem_file8_t := init_imem('1', application_init_image);

  -- internal "ROM" type - implemented if bootloader is NOT used; always initialize with app code --

  constant imem_file_rom_l : imem_file8_t := init_imem('0', application_init_image);

  constant imem_file_rom_h : imem_file8_t := init_imem('1', application_init_image);

  -- internal "RAM" type - implemented if bootloader is used and IMEM is RAM --

  signal imem_file_ram_l : imem_file8_t;

  signal imem_file_ram_h : imem_file8_t;

  -- RAM attribute to inhibit bypass-logic - Intel only! --

  attribute ramstyle : string;

  attribute ramstyle of imem_file_init_ram_l : signal is "no_rw_check";

  attribute ramstyle of imem_file_init_ram_h : signal is "no_rw_check";

  attribute ramstyle of imem_file_ram_l : signal is "no_rw_check";

  attribute ramstyle of imem_file_ram_h : signal is "no_rw_check";

  -- RAM attribute to inhibit bypass-logic - Lattice only! --

  attribute syn_ramstyle : string;

  attribute syn_ramstyle of imem_file_init_ram_l : signal is "no_rw_check";

  attribute syn_ramstyle of imem_file_init_ram_h : signal is "no_rw_check";

  attribute syn_ramstyle of imem_file_ram_l : signal is "no_rw_check";

  attribute syn_ramstyle of imem_file_ram_h : signal is "no_rw_check";

begin

  -- Access Control -----------------------------------------------------------

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

  acc_en <= '1' when (addr_i >= imem_base_c) and (addr_i < std_ulogic_vector(unsigned(imem_base_c) + IMEM_SIZE)) else '0';

  addr   <= to_integer(unsigned(addr_i(index_size_f(IMEM_SIZE/2) downto 1))); -- word aligned

  -- Memory Access ------------------------------------------------------------

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

  imem_file_access: process(clk_i)

  begin

    -- check max size --

    if (IMEM_SIZE > imem_max_size_c) then

      assert false report "I-mem size out of range! Max 48kB!" severity error;

    end if;

    -- actual memory access --

    if rising_edge(clk_i) then

      rden <= rden_i and acc_en;

      if (acc_en = '1') then -- reduce switching activity when not accessed

        if (IMEM_AS_ROM = true) then -- implement IMEM as true ROM

          rdata(07 downto 0) <= imem_file_rom_l(addr);

          rdata(15 downto 8) <= imem_file_rom_h(addr);

        elsif (BOOTLD_USE = true) then -- implement IMEM as non-initialized RAM

          if (wren_i(0) = '1') and (upen_i = '1') then

            imem_file_ram_l(addr) <= data_i(07 downto 0);

          end if;

          rdata(07 downto 0) <= imem_file_ram_l(addr);

          if (wren_i(1) = '1') and (upen_i = '1') then

            imem_file_ram_h(addr) <= data_i(15 downto 8);

          end if;

          rdata(15 downto 8) <= imem_file_ram_h(addr);

        else -- implement IMEM as PRE-INITIALIZED RAM

          if (wren_i(0) = '1') and (upen_i = '1') then

            imem_file_init_ram_l(addr) <= data_i(07 downto 0);

          end if;

          rdata(07 downto 0) <= imem_file_init_ram_l(addr);

          if (wren_i(1) = '1') and (upen_i = '1') then

            imem_file_init_ram_h(addr) <= data_i(15 downto 8);

          end if;

          rdata(15 downto 8) <= imem_file_init_ram_h(addr);

        end if;

      end if;

    end if;

  end process imem_file_access;

  -- output gate --

  data_o <= rdata when (rden = '1') else (others => '0');

end neo430_imem_rtl;