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

-- # << NEORV32 - Processor-internal instruction memory (IMEM) >>                                  #

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

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

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

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

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2021, 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 NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neorv32;

use neorv32.neorv32_package.all;

use neorv32.neorv32_application_image.all; -- this file is generated by the image generator

architecture neorv32_imem_rtl of neorv32_imem is

  -- IO space: module base address --

  constant hi_abb_c : natural := 31; -- high address boundary bit

  constant lo_abb_c : natural := index_size_f(IMEM_SIZE); -- low address boundary bit

  -- local signals --

  signal acc_en : std_ulogic;

  signal rdata  : std_ulogic_vector(31 downto 0);

  signal rden   : std_ulogic;

  signal addr   : std_ulogic_vector(index_size_f(IMEM_SIZE/4)-1 downto 0);

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

  -- IMEM as pre-initialized ROM --

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

  -- application (image) size in bytes --

  constant imem_app_size_c : natural := (application_init_image'length)*4;

  -- ROM - initialized with executable code --

  constant mem_rom : mem32_t(0 to IMEM_SIZE/4-1) := mem32_init_f(application_init_image, IMEM_SIZE/4);

  -- read data --

  signal mem_rom_rd : std_ulogic_vector(31 downto 0);

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

  -- The memory (RAM) is built from 4 individual byte-wide memories b0..b3, since some synthesis tools have         --

  -- problems with 32-bit memories that provide dedicated byte-enable signals AND/OR with multi-dimensional arrays. --

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

  -- RAM - not initialized at all --

  signal mem_ram_b0 : mem8_t(0 to IMEM_SIZE/4-1);

  signal mem_ram_b1 : mem8_t(0 to IMEM_SIZE/4-1);

  signal mem_ram_b2 : mem8_t(0 to IMEM_SIZE/4-1);

  signal mem_ram_b3 : mem8_t(0 to IMEM_SIZE/4-1);

  -- read data --

  signal mem_b0_rd, mem_b1_rd, mem_b2_rd, mem_b3_rd : std_ulogic_vector(7 downto 0);

begin

  -- Sanity Checks --------------------------------------------------------------------------

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

  assert false report "NEORV32 PROCESSOR CONFIG NOTE: Using DEFAULT platform-agnostic IMEM." severity note;

  assert not (IMEM_AS_IROM = true)  report "NEORV32 PROCESSOR CONFIG NOTE: Implementing processor-internal IMEM as ROM (" & natural'image(IMEM_SIZE) &

  " bytes), pre-initialized with application (" & natural'image(imem_app_size_c) & " bytes)." severity note;

  --

  assert not (IMEM_AS_IROM = false) report "NEORV32 PROCESSOR CONFIG NOTE: Implementing processor-internal IMEM as blank RAM (" & natural'image(IMEM_SIZE) &

  " bytes)." severity note;

  --

  assert not ((IMEM_AS_IROM = true) and (imem_app_size_c > IMEM_SIZE)) report "NEORV32 PROCESSOR CONFIG ERROR: Application (image = " & natural'image(imem_app_size_c) &

  " bytes) does not fit into processor-internal IMEM (ROM = " & natural'image(IMEM_SIZE) & " bytes)!" severity error;

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

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

  acc_en <= '1' when (addr_i(hi_abb_c downto lo_abb_c) = IMEM_BASE(hi_abb_c downto lo_abb_c)) else '0';

  addr   <= addr_i(index_size_f(IMEM_SIZE/4)+1 downto 2); -- word aligned

  -- Implement IMEM as pre-initialized ROM --------------------------------------------------

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

  imem_rom:

  if (IMEM_AS_IROM = true) generate

    mem_access: process(clk_i)

    begin

      if rising_edge(clk_i) then

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

          mem_rom_rd <= mem_rom(to_integer(unsigned(addr)));

        end if;

      end if;

    end process mem_access;

    -- read data --

    rdata <= mem_rom_rd;

  end generate;

  -- Implement IMEM as not-initialized RAM --------------------------------------------------

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

  imem_ram:

  if (IMEM_AS_IROM = false) generate

    mem_access: process(clk_i)

    begin

      if rising_edge(clk_i) then

        -- this RAM style should not require "no_rw_check" attributes as the read-after-write behavior

        -- is intended to be defined implicitly via the if-WRITE-else-READ construct

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

          if (wren_i = '1') and (ben_i(0) = '1') then -- byte 0

            mem_ram_b0(to_integer(unsigned(addr))) <= data_i(07 downto 00);

          else

            mem_b0_rd <= mem_ram_b0(to_integer(unsigned(addr)));

          end if;

          if (wren_i = '1') and (ben_i(1) = '1') then -- byte 1

            mem_ram_b1(to_integer(unsigned(addr))) <= data_i(15 downto 08);

          else

            mem_b1_rd <= mem_ram_b1(to_integer(unsigned(addr)));

          end if;

          if (wren_i = '1') and (ben_i(2) = '1') then -- byte 2

            mem_ram_b2(to_integer(unsigned(addr))) <= data_i(23 downto 16);

          else

            mem_b2_rd <= mem_ram_b2(to_integer(unsigned(addr)));

          end if;

          if (wren_i = '1') and (ben_i(3) = '1') then -- byte 3

            mem_ram_b3(to_integer(unsigned(addr))) <= data_i(31 downto 24);

          else

            mem_b3_rd <= mem_ram_b3(to_integer(unsigned(addr)));

          end if;

        end if;

      end if;

    end process mem_access;

    -- read data --

    rdata <= mem_b3_rd & mem_b2_rd & mem_b1_rd & mem_b0_rd;

  end generate;

  -- Bus Feedback ---------------------------------------------------------------------------

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

  bus_feedback: process(clk_i)

  begin

    if rising_edge(clk_i) then

      rden <= acc_en and rden_i;

      if (IMEM_AS_IROM = true) then

        ack_o <= acc_en and rden_i;

      else

        ack_o <= acc_en and (rden_i or wren_i);

      end if;

    end if;

  end process bus_feedback;

  -- output gate --

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

end neorv32_imem_rtl;