-- #################################################################################################
-- # << NEORV32 - Processor-internal instruction memory (IMEM) >>                                  #
-- # ********************************************************************************************* #
-- # This version is intended for SIMULATION ONLY!                                                 #
-- # It implements the IMEM as pre-initialized RAM.                                                #
-- # ********************************************************************************************* #
-- # 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);

  -- ---------------------------------------------------- --
  -- << SIMULATION ONLY!!! >> IMEM as pre-initialized RAM --
  -- ---------------------------------------------------- --

  -- application (image) size in bytes --
  constant imem_app_size_c : natural := (application_init_image'length)*4;

  -- RAM - initialized with executable code --
  signal mem_ram : mem32_t(0 to IMEM_SIZE/4-1) := mem32_init_f(application_init_image, IMEM_SIZE/4);

  -- read data --
  signal mem_ram_rd : std_ulogic_vector(31 downto 0);

begin

  -- Sanity Checks --------------------------------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  assert false report "NEORV32 PROCESSOR CONFIG NOTE: Implementing processor-internal [SIM-only!] IMEM as RAM (" & natural'image(IMEM_SIZE) &
  " bytes), pre-initialized with application (" & natural'image(imem_app_size_c) & " bytes)." severity note;
  --
  assert not (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 (" & 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 RAM --------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  mem_access: process(clk_i)
  begin
    if rising_edge(clk_i) then
      if (acc_en = '1') then
        if (wren_i = '1') and (ben_i(0) = '1') then -- byte 0
          mem_ram(to_integer(unsigned(addr)))(07 downto 00) <= data_i(07 downto 00);
        else
          mem_ram_rd(07 downto 00) <= mem_ram(to_integer(unsigned(addr)))(07 downto 00);
        end if;
        if (wren_i = '1') and (ben_i(1) = '1') then -- byte 1
          mem_ram(to_integer(unsigned(addr)))(15 downto 08) <= data_i(15 downto 08);
        else
          mem_ram_rd(15 downto 08) <= mem_ram(to_integer(unsigned(addr)))(15 downto 08);
        end if;
        if (wren_i = '1') and (ben_i(2) = '1') then -- byte 2
          mem_ram(to_integer(unsigned(addr)))(23 downto 16) <= data_i(23 downto 16);
        else
          mem_ram_rd(23 downto 16) <= mem_ram(to_integer(unsigned(addr)))(23 downto 16);
        end if;
        if (wren_i = '1') and (ben_i(3) = '1') then -- byte 3
          mem_ram(to_integer(unsigned(addr)))(31 downto 24) <= data_i(31 downto 24);
        else
          mem_ram_rd(31 downto 24) <= mem_ram(to_integer(unsigned(addr)))(31 downto 24);
        end if;
      end if;
    end if;
  end process mem_access;

  -- read data --
  rdata <= mem_ram_rd;


  -- Bus Feedback ---------------------------------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  bus_feedback: process(clk_i)
  begin
    if rising_edge(clk_i) then
      rden  <= acc_en and rden_i;
      ack_o <= acc_en and (rden_i or wren_i);
    end if;
  end process bus_feedback;

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


end neorv32_imem_rtl;