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

-- # << NEORV32 - Processor-Internal Instruction Cache >>                                          #

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

-- # Direct mapped (ICACHE_NUM_SETS = 1) or 2-way set-associative (ICACHE_NUM_SETS = 2).           #

-- # Least recently used replacement policy (if ICACHE_NUM_SETS > 1).                              #

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

-- # 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;

entity neorv32_icache is

  generic (

    ICACHE_NUM_BLOCKS : natural := 4;  -- number of blocks (min 1), has to be a power of 2

    ICACHE_BLOCK_SIZE : natural := 16; -- block size in bytes (min 4), has to be a power of 2

    ICACHE_NUM_SETS   : natural := 1   -- associativity / number of sets (1=direct_mapped), has to be a power of 2

  );

  port (

    -- global control --

    clk_i         : in  std_ulogic; -- global clock, rising edge

    rstn_i        : in  std_ulogic; -- global reset, low-active, async

    clear_i       : in  std_ulogic; -- cache clear

    -- host controller interface --

    host_addr_i   : in  std_ulogic_vector(data_width_c-1 downto 0); -- bus access address

    host_rdata_o  : out std_ulogic_vector(data_width_c-1 downto 0); -- bus read data

    host_wdata_i  : in  std_ulogic_vector(data_width_c-1 downto 0); -- bus write data

    host_ben_i    : in  std_ulogic_vector(03 downto 0); -- byte enable

    host_we_i     : in  std_ulogic; -- write enable

    host_re_i     : in  std_ulogic; -- read enable

    host_cancel_i : in  std_ulogic; -- cancel current bus transaction

    host_ack_o    : out std_ulogic; -- bus transfer acknowledge

    host_err_o    : out std_ulogic; -- bus transfer error

    -- peripheral bus interface --

    bus_addr_o    : out std_ulogic_vector(data_width_c-1 downto 0); -- bus access address

    bus_rdata_i   : in  std_ulogic_vector(data_width_c-1 downto 0); -- bus read data

    bus_wdata_o   : out std_ulogic_vector(data_width_c-1 downto 0); -- bus write data

    bus_ben_o     : out std_ulogic_vector(03 downto 0); -- byte enable

    bus_we_o      : out std_ulogic; -- write enable

    bus_re_o      : out std_ulogic; -- read enable

    bus_cancel_o  : out std_ulogic; -- cancel current bus transaction

    bus_ack_i     : in  std_ulogic; -- bus transfer acknowledge

    bus_err_i     : in  std_ulogic  -- bus transfer error

  );

end neorv32_icache;

architecture neorv32_icache_rtl of neorv32_icache is

  -- cache layout --

  constant cache_offset_size_c : natural := index_size_f(ICACHE_BLOCK_SIZE/4); -- offset addresses full 32-bit words

  constant cache_index_size_c  : natural := index_size_f(ICACHE_NUM_BLOCKS);

  constant cache_tag_size_c    : natural := 32 - (cache_offset_size_c + cache_index_size_c + 2); -- 2 additonal bits for byte offset

  -- cache memory --

  component neorv32_icache_memory

  generic (

    ICACHE_NUM_BLOCKS : natural := 4;  -- number of blocks (min 1), has to be a power of 2

    ICACHE_BLOCK_SIZE : natural := 16; -- block size in bytes (min 4), has to be a power of 2

    ICACHE_NUM_SETS   : natural := 1   -- associativity; 0=direct-mapped, 1=2-way set-associative

  );

  port (

    -- global control --

    clk_i          : in  std_ulogic; -- global clock, rising edge

    invalidate_i   : in  std_ulogic; -- invalidate whole cache

    -- host cache access (read-only) --

    host_addr_i    : in  std_ulogic_vector(31 downto 0); -- access address

    host_re_i      : in  std_ulogic; -- read enable

    host_rdata_o   : out std_ulogic_vector(31 downto 0); -- read data

    -- access status (1 cycle delay to access) --

    hit_o          : out std_ulogic; -- hit access

    -- ctrl cache access (write-only) --

    ctrl_en_i      : in  std_ulogic; -- control interface enable

    ctrl_addr_i    : in  std_ulogic_vector(31 downto 0); -- access address

    ctrl_we_i      : in  std_ulogic; -- write enable (full-word)

    ctrl_wdata_i   : in  std_ulogic_vector(31 downto 0); -- write data

    ctrl_tag_we_i  : in  std_ulogic; -- write tag to selected block

    ctrl_valid_i   : in  std_ulogic; -- make selected block valid

    ctrl_invalid_i : in  std_ulogic  -- make selected block invalid

  );

  end component;

  -- cache interface --

  type cache_if_t is record

    clear           : std_ulogic; -- cache clear

    --

    host_addr       : std_ulogic_vector(31 downto 0); -- cpu access address

    host_rdata      : std_ulogic_vector(31 downto 0); -- cpu read data

    --

    hit             : std_ulogic; -- hit access

    --

    ctrl_en         : std_ulogic; -- control access enable

    ctrl_addr       : std_ulogic_vector(31 downto 0); -- control access address

    ctrl_we         : std_ulogic; -- control write enable

    ctrl_wdata      : std_ulogic_vector(31 downto 0); -- control write data

    ctrl_tag_we     : std_ulogic; -- control tag write enabled

    ctrl_valid_we   : std_ulogic; -- control valid flag set

    ctrl_invalid_we : std_ulogic; -- control valid flag clear

  end record;

  signal cache : cache_if_t;

  -- control engine --

  type ctrl_engine_state_t is (S_IDLE, S_CACHE_CLEAR, S_CACHE_CHECK, S_CACHE_MISS, S_BUS_DOWNLOAD_REQ, S_BUS_DOWNLOAD_GET,

                               S_CACHE_RESYNC_0, S_CACHE_RESYNC_1, S_BUS_ERROR, S_ERROR, S_HOST_CANCEL);

  type ctrl_t is record

    state          : ctrl_engine_state_t; -- current state

    state_nxt      : ctrl_engine_state_t; -- next state

    addr_reg       : std_ulogic_vector(31 downto 0); -- address register for block download

    addr_reg_nxt   : std_ulogic_vector(31 downto 0);

    --

    re_buf         : std_ulogic; -- read request buffer

    re_buf_nxt     : std_ulogic;

    cancel_buf     : std_ulogic; -- cancel request buffer

    cancel_buf_nxt : std_ulogic;

  end record;

  signal ctrl : ctrl_t;

begin

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

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

  -- configuration --

  assert not (is_power_of_two_f(ICACHE_NUM_BLOCKS) = false) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache number of blocks <ICACHE_NUM_BLOCKS> has to be a power of 2." severity error;

  assert not (is_power_of_two_f(ICACHE_BLOCK_SIZE) = false) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache block size <ICACHE_BLOCK_SIZE> has to be a power of 2." severity error;

  assert not ((is_power_of_two_f(ICACHE_NUM_SETS) = false)) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache associativity <ICACHE_NUM_SETS> has to be a power of 2." severity error;

  assert not (ICACHE_NUM_BLOCKS < 1) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache number of blocks <ICACHE_NUM_BLOCKS> has to be >= 1." severity error;

  assert not (ICACHE_BLOCK_SIZE < 4) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache block size <ICACHE_BLOCK_SIZE> has to be >= 4." severity error;

  assert not ((ICACHE_NUM_SETS = 0) or (ICACHE_NUM_SETS > 2)) report "NEORV32 PROCESSOR CONFIG ERROR! i-cache associativity <ICACHE_NUM_SETS> has to be 1 (direct-mapped) or 2 (2-way set-associative)." severity error;

  -- Control Engine FSM Sync ----------------------------------------------------------------

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

  -- registers that REQUIRE a specific reset state --

  ctrl_engine_fsm_sync_rst: process(rstn_i, clk_i)

  begin

    if (rstn_i = '0') then

      ctrl.state      <= S_CACHE_CLEAR;

      ctrl.re_buf     <= '0';

      ctrl.cancel_buf <= '0';

    elsif rising_edge(clk_i) then

      ctrl.state      <= ctrl.state_nxt;

      ctrl.re_buf     <= ctrl.re_buf_nxt;

      ctrl.cancel_buf <= ctrl.cancel_buf_nxt;

    end if;

  end process ctrl_engine_fsm_sync_rst;

  -- registers that do not require a specific reset state --

  ctrl_engine_fsm_sync: process(clk_i)

  begin

    if rising_edge(clk_i) then

      ctrl.addr_reg <= ctrl.addr_reg_nxt;

    end if;

  end process ctrl_engine_fsm_sync;

  -- Control Engine FSM Comb ----------------------------------------------------------------

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

  ctrl_engine_fsm_comb: process(ctrl, cache, clear_i, host_addr_i, host_re_i, host_cancel_i, bus_rdata_i, bus_ack_i, bus_err_i)

  begin

    -- control defaults --

    ctrl.state_nxt        <= ctrl.state;

    ctrl.addr_reg_nxt     <= ctrl.addr_reg;

    ctrl.re_buf_nxt       <= (ctrl.re_buf    or host_re_i) and (not host_cancel_i);

    ctrl.cancel_buf_nxt   <= ctrl.cancel_buf or host_cancel_i;

    -- cache defaults --

    cache.clear           <= '0';

    cache.host_addr       <= host_addr_i;

    cache.ctrl_en         <= '0';

    cache.ctrl_addr       <= ctrl.addr_reg;

    cache.ctrl_we         <= '0';

    cache.ctrl_wdata      <= bus_rdata_i;

    cache.ctrl_tag_we     <= '0';

    cache.ctrl_valid_we   <= '0';

    cache.ctrl_invalid_we <= '0';

    -- host interface defaults --

    host_ack_o            <= '0';

    host_err_o            <= '0';

    host_rdata_o          <= cache.host_rdata;

    -- peripheral bus interface defaults --

    bus_addr_o            <= ctrl.addr_reg;

    bus_wdata_o           <= (others => '0'); -- cache is read-only

    bus_ben_o             <= (others => '0'); -- cache is read-only

    bus_we_o              <= '0'; -- cache is read-only

    bus_re_o              <= '0';

    bus_cancel_o          <= '0';

    -- fsm --

    case ctrl.state is

      when S_IDLE => -- wait for host access request or cache control operation

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

        if (clear_i = '1') then -- cache control operation?

          ctrl.state_nxt <= S_CACHE_CLEAR;

        elsif (host_re_i = '1') or (ctrl.re_buf = '1') then -- cache access

          ctrl.re_buf_nxt     <= '0';

          ctrl.cancel_buf_nxt <= '0';

          ctrl.state_nxt      <= S_CACHE_CHECK;

        end if;

      when S_CACHE_CLEAR => -- invalidate all cache entries

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

        cache.clear    <= '1';

        ctrl.state_nxt <= S_IDLE;

      when S_CACHE_CHECK => -- finalize host access if cache hit

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

        if (cache.hit = '1') then -- cache HIT

          host_ack_o     <= not ctrl.cancel_buf; -- ACK if request has not been canceled

          ctrl.state_nxt <= S_IDLE;

        else -- cache MISS

          ctrl.state_nxt <= S_CACHE_MISS;

        end if;

      when S_CACHE_MISS => -- 

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

        -- compute block base address --

        ctrl.addr_reg_nxt <= host_addr_i;

        ctrl.addr_reg_nxt((2+cache_offset_size_c)-1 downto 2) <= (others => '0'); -- block-aligned

        ctrl.addr_reg_nxt(1 downto 0) <= "00"; -- word-aligned

        --

        if (host_cancel_i = '1') or (ctrl.cancel_buf = '1') then -- 'early' CPU cancel (abort before bus transaction has even started)

          ctrl.state_nxt <= S_IDLE;

        else

          ctrl.state_nxt <= S_BUS_DOWNLOAD_REQ;

        end if;

      when S_BUS_DOWNLOAD_REQ => -- download new cache block: request new word

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

        bus_re_o       <= '1'; -- request new read transfer

        ctrl.state_nxt <= S_BUS_DOWNLOAD_GET;

      when S_BUS_DOWNLOAD_GET => -- download new cache block: wait for bus response

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

        cache.ctrl_en <= '1'; -- we are in cache control mode

        --

        if (bus_err_i = '1') then -- bus error

          ctrl.state_nxt <= S_BUS_ERROR;

        elsif (ctrl.cancel_buf = '1') then -- 'late' CPU cancel (timeout?)

          ctrl.state_nxt <= S_HOST_CANCEL;

        elsif (bus_ack_i = '1') then -- ACK = write to cache and get next word

          cache.ctrl_we <= '1'; -- write to cache

          if (and_all_f(ctrl.addr_reg((2+cache_offset_size_c)-1 downto 2)) = '1') then -- block complete?

            cache.ctrl_tag_we   <= '1'; -- current block is valid now

            cache.ctrl_valid_we <= '1'; -- write tag of current address

            ctrl.state_nxt      <= S_CACHE_RESYNC_0;

          else -- get next word

            ctrl.addr_reg_nxt <= std_ulogic_vector(unsigned(ctrl.addr_reg) + 4);

            ctrl.state_nxt    <= S_BUS_DOWNLOAD_REQ;

          end if;

        end if;

      when S_CACHE_RESYNC_0 => -- re-sync host/cache access: cache read-latency

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

        ctrl.state_nxt <= S_CACHE_RESYNC_1;

      when S_CACHE_RESYNC_1 => -- re-sync host/cache access: finalize CPU request

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

        host_ack_o     <= not ctrl.cancel_buf; -- ACK if request has not been canceled

        ctrl.state_nxt <= S_IDLE;

      when S_BUS_ERROR => -- bus error during download

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

        host_err_o     <= '1';

        ctrl.state_nxt <= S_ERROR;

      when S_ERROR => -- wait for CPU to cancel faulting transfer

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

        if (host_cancel_i = '1') then

          bus_cancel_o   <= '1';

          ctrl.state_nxt <= S_IDLE;

        end if;

      when S_HOST_CANCEL => -- host cancels transfer

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

        cache.ctrl_en         <= '1'; -- we are in cache control mode

        cache.ctrl_invalid_we <= '1'; -- invalidate current cache block

        bus_cancel_o          <= '1';

        ctrl.state_nxt        <= S_IDLE;

      when others => -- undefined

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

        ctrl.state_nxt <= S_IDLE;

    end case;

  end process ctrl_engine_fsm_comb;

        -- Cache Memory ---------------------------------------------------------------------------

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

  neorv32_icache_memory_inst: neorv32_icache_memory

  generic map (

    ICACHE_NUM_BLOCKS => ICACHE_NUM_BLOCKS,     -- number of blocks (min 1), has to be a power of 2

    ICACHE_BLOCK_SIZE => ICACHE_BLOCK_SIZE,     -- block size in bytes (min 4), has to be a power of 2

    ICACHE_NUM_SETS   => ICACHE_NUM_SETS        -- associativity; 0=direct-mapped, 1=2-way set-associative

  )

  port map (

    -- global control --

    clk_i            => clk_i,                -- global clock, rising edge

    invalidate_i     => cache.clear,          -- invalidate whole cache

    -- host cache access (read-only)          --

    host_addr_i      => cache.host_addr,      -- access address

    host_re_i        => host_re_i,            -- read enable

    host_rdata_o     => cache.host_rdata,     -- read data

    -- access status (1 cycle delay to access) --

    hit_o            => cache.hit,            -- hit access

    -- ctrl cache access (write-only) --

    ctrl_en_i        => cache.ctrl_en,        -- control interface enable

    ctrl_addr_i      => cache.ctrl_addr,      -- access address

    ctrl_we_i        => cache.ctrl_we,        -- write enable (full-word)

    ctrl_wdata_i     => cache.ctrl_wdata,     -- write data

    ctrl_tag_we_i    => cache.ctrl_tag_we,    -- write tag to selected block

    ctrl_valid_i     => cache.ctrl_valid_we,  -- make selected block valid

    ctrl_invalid_i   => cache.ctrl_invalid_we -- make selected block invalid

  );

end neorv32_icache_rtl;

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

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

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

-- # << NEORV32 - Cache Memory >>                                                                  #

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

-- # Direct mapped (ICACHE_NUM_SETS = 1) or 2-way set-associative (ICACHE_NUM_SETS = 2).           #

-- # Least recently used replacement policy (if ICACHE_NUM_SETS > 1).                              #

-- # Read-only for host, write-only for control. All output signals have one cycle latency.        #

-- #                                                                                               #

-- # Cache sets are mapped to individual memory components - no multi-dimensional memory arrays    #

-- # are used as some synthesis tools have problems to map these to actual BRAM primitives.        #

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

-- # 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 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;

entity neorv32_icache_memory is

  generic (

    ICACHE_NUM_BLOCKS : natural := 4;  -- number of blocks (min 1), has to be a power of 2

    ICACHE_BLOCK_SIZE : natural := 16; -- block size in bytes (min 4), has to be a power of 2

    ICACHE_NUM_SETS   : natural := 1   -- associativity; 1=direct-mapped, 2=2-way set-associative

  );

  port (

    -- global control --

    clk_i            : in  std_ulogic; -- global clock, rising edge

    invalidate_i     : in  std_ulogic; -- invalidate whole cache

    -- host cache access (read-only) --

    host_addr_i      : in  std_ulogic_vector(31 downto 0); -- access address

    host_re_i        : in  std_ulogic; -- read enable

    host_rdata_o     : out std_ulogic_vector(31 downto 0); -- read data

    -- access status (1 cycle delay to access) --

    hit_o            : out std_ulogic; -- hit access

    -- ctrl cache access (write-only) --

    ctrl_en_i        : in  std_ulogic; -- control interface enable

    ctrl_addr_i      : in  std_ulogic_vector(31 downto 0); -- access address

    ctrl_we_i        : in  std_ulogic; -- write enable (full-word)

    ctrl_wdata_i     : in  std_ulogic_vector(31 downto 0); -- write data

    ctrl_tag_we_i    : in  std_ulogic; -- write tag to selected block

    ctrl_valid_i     : in  std_ulogic; -- make selected block valid

    ctrl_invalid_i   : in  std_ulogic  -- make selected block invalid

  );

end neorv32_icache_memory;

architecture neorv32_icache_memory_rtl of neorv32_icache_memory is

  -- cache layout --

  constant cache_offset_size_c : natural := index_size_f(ICACHE_BLOCK_SIZE/4); -- offset addresses full 32-bit words

  constant cache_index_size_c  : natural := index_size_f(ICACHE_NUM_BLOCKS);

  constant cache_tag_size_c    : natural := 32 - (cache_offset_size_c + cache_index_size_c + 2); -- 2 additonal bits for byte offset

  constant cache_entries_c     : natural := ICACHE_NUM_BLOCKS * (ICACHE_BLOCK_SIZE/4); -- number of 32-bit entries (per set)

  -- status flag memory --

  signal valid_flag_s0 : std_ulogic_vector(ICACHE_NUM_BLOCKS-1 downto 0);

  signal valid_flag_s1 : std_ulogic_vector(ICACHE_NUM_BLOCKS-1 downto 0);

  signal valid         : std_ulogic_vector(1 downto 0); -- valid flag read data

  -- tag memory --

  type tag_mem_t is array (0 to ICACHE_NUM_BLOCKS-1) of std_ulogic_vector(cache_tag_size_c-1 downto 0);

  signal tag_mem_s0 : tag_mem_t;

  signal tag_mem_s1 : tag_mem_t;

  type tag_rd_t is array (0 to 1) of std_ulogic_vector(cache_tag_size_c-1 downto 0);

  signal tag : tag_rd_t; -- tag read data

  -- access status --

  signal hit : std_ulogic_vector(1 downto 0);

  -- access address decomposition --

  type acc_addr_t is record

    tag    : std_ulogic_vector(cache_tag_size_c-1 downto 0);

    index  : std_ulogic_vector(cache_index_size_c-1 downto 0);

    offset : std_ulogic_vector(cache_offset_size_c-1 downto 0);

  end record;

  signal host_acc_addr, ctrl_acc_addr : acc_addr_t;

  -- cache data memory --

  type cache_mem_t is array (0 to cache_entries_c-1) of std_ulogic_vector(31 downto 0);

  signal cache_data_memory_s0 : cache_mem_t; -- set 0

  signal cache_data_memory_s1 : cache_mem_t; -- set 1

  -- cache data memory access --

  type cache_rdata_t is array (0 to 1) of std_ulogic_vector(31 downto 0);

  signal cache_rdata  : cache_rdata_t;

  signal cache_index  : std_ulogic_vector(cache_index_size_c-1 downto 0);

  signal cache_offset : std_ulogic_vector(cache_offset_size_c-1 downto 0);

  signal cache_addr   : std_ulogic_vector((cache_index_size_c+cache_offset_size_c)-1 downto 0); -- index & offset

  signal cache_we     : std_ulogic; -- write enable (full-word)

  signal set_select   : std_ulogic;

  -- access history --

  type history_t is record

    re_ff          : std_ulogic;

    last_used_set  : std_ulogic_vector(ICACHE_NUM_BLOCKS-1 downto 0);

    to_be_replaced : std_ulogic;

  end record;

  signal history : history_t;

begin

        -- Access Address Decomposition -----------------------------------------------------------

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

  host_acc_addr.tag    <= host_addr_i(31 downto 31-(cache_tag_size_c-1));

  host_acc_addr.index  <= host_addr_i(31-cache_tag_size_c downto 2+cache_offset_size_c);

  host_acc_addr.offset <= host_addr_i(2+(cache_offset_size_c-1) downto 2); -- discard byte offset

  ctrl_acc_addr.tag    <= ctrl_addr_i(31 downto 31-(cache_tag_size_c-1));

  ctrl_acc_addr.index  <= ctrl_addr_i(31-cache_tag_size_c downto 2+cache_offset_size_c);

  ctrl_acc_addr.offset <= ctrl_addr_i(2+(cache_offset_size_c-1) downto 2); -- discard byte offset

        -- Cache Access History -------------------------------------------------------------------

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

  access_history: process(clk_i)

  begin

    if rising_edge(clk_i) then

      history.re_ff <= host_re_i;

      if (invalidate_i = '1') then -- invalidate whole cache

        history.last_used_set <= (others => '1');

      elsif (history.re_ff = '1') and (or_all_f(hit) = '1') then -- store last accessed set that caused a hit

        history.last_used_set(to_integer(unsigned(cache_index))) <= not hit(0);

      end if;

      history.to_be_replaced <= history.last_used_set(to_integer(unsigned(cache_index)));

    end if;

  end process access_history;

  -- which set is going to be replaced? -> opposite of last used set = least recently used set --

  set_select <= '0' when (ICACHE_NUM_SETS = 1) else (not history.to_be_replaced);

        -- Status flag memory ---------------------------------------------------------------------

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

  status_memory: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- write access --

      if (invalidate_i = '1') then -- invalidate whole cache

        valid_flag_s0 <= (others => '0');

        valid_flag_s1 <= (others => '0');

      elsif (ctrl_en_i = '1') then

        if (ctrl_invalid_i = '1') then -- make current block invalid

          if (set_select = '0') then

            valid_flag_s0(to_integer(unsigned(cache_index))) <= '0';

          else

            valid_flag_s1(to_integer(unsigned(cache_index))) <= '0';

          end if;

        elsif (ctrl_valid_i = '1') then -- make current block valid

          if (set_select = '0') then

            valid_flag_s0(to_integer(unsigned(cache_index))) <= '1';

          else

            valid_flag_s1(to_integer(unsigned(cache_index))) <= '1';

          end if;

        end if;

      end if;

      -- read access (sync) --

      valid(0) <= valid_flag_s0(to_integer(unsigned(cache_index)));

      valid(1) <= valid_flag_s1(to_integer(unsigned(cache_index)));

    end if;

  end process status_memory;

        -- Tag memory -----------------------------------------------------------------------------

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

  tag_memory: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (ctrl_en_i = '1') and (ctrl_tag_we_i = '1') then -- write access

        if (set_select = '0') then

          tag_mem_s0(to_integer(unsigned(cache_index))) <= ctrl_acc_addr.tag;

        else

          tag_mem_s1(to_integer(unsigned(cache_index))) <= ctrl_acc_addr.tag;

        end if;

      else -- read access

        tag(0) <= tag_mem_s0(to_integer(unsigned(cache_index)));

        tag(1) <= tag_mem_s1(to_integer(unsigned(cache_index)));

      end if;

    end if;

  end process tag_memory;

  -- comparator --

  comparator: process(host_acc_addr, tag, valid)

  begin

    hit <= (others => '0');

    for i in 0 to ICACHE_NUM_SETS-1 loop

      if (host_acc_addr.tag = tag(i)) and (valid(i) = '1') then

        hit(i) <= '1';

      end if;

    end loop; -- i

  end process comparator;

  -- global hit --

  hit_o <= or_all_f(hit);

        -- Cache Data Memory ----------------------------------------------------------------------

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

  cache_mem_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (cache_we = '1') then -- write access from control (full-word)

        if (set_select = '0') then

          cache_data_memory_s0(to_integer(unsigned(cache_addr))) <= ctrl_wdata_i;

        else

          cache_data_memory_s1(to_integer(unsigned(cache_addr))) <= ctrl_wdata_i;

        end if;

      else -- read access from host (full-word)

        cache_rdata(0) <= cache_data_memory_s0(to_integer(unsigned(cache_addr)));

        cache_rdata(1) <= cache_data_memory_s1(to_integer(unsigned(cache_addr)));

      end if;

    end if;

  end process cache_mem_access;

  -- data output --

  host_rdata_o <= cache_rdata(0) when (hit(0) = '1') or (ICACHE_NUM_SETS = 1) else cache_rdata(1);

  -- cache block ram access address --

  cache_addr <= cache_index & cache_offset;

  -- cache access select --

  cache_index  <= host_acc_addr.index  when (ctrl_en_i = '0') else ctrl_acc_addr.index;

  cache_offset <= host_acc_addr.offset when (ctrl_en_i = '0') else ctrl_acc_addr.offset;

  cache_we     <= '0'                  when (ctrl_en_i = '0') else ctrl_we_i;

end neorv32_icache_memory_rtl;