Subversion Repositories neorv32

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

-- # << NEORV32 - Processor-internal bootloader ROM (BOOTROM) >>                                   #

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-- # BSD 3-Clause License                                                                          #

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

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-- # 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_bootloader_image.all; -- this file is generated by the image generator

entity neorv32_boot_rom is

  generic (

    BOOTROM_BASE : std_ulogic_vector(31 downto 0) := x"FFFF0000"; -- boot ROM base address

    BOOTROM_SIZE : natural := 4*1024  -- processor-internal boot ROM memory size in bytes

  );

  port (

    clk_i  : in  std_ulogic; -- global clock line

    rden_i : in  std_ulogic; -- read enable

    addr_i : in  std_ulogic_vector(31 downto 0); -- address

    data_o : out std_ulogic_vector(31 downto 0); -- data out

    ack_o  : out std_ulogic -- transfer acknowledge

  );

end neorv32_boot_rom;

architecture neorv32_boot_rom_rtl of neorv32_boot_rom is

  -- local types --

  type boot_img_t is array (0 to BOOTROM_SIZE/4-1) of std_ulogic_vector(31 downto 0);

  -- init function --

  -- impure function: returns NOT the same result every time it is evaluated with the same arguments since the source file might have changed

  impure function init_boot_rom(init : bootloader_init_image_t) return boot_img_t is

    variable mem_v : boot_img_t;

  begin

    mem_v := (others => (others => '0'));

    for i in 0 to init'length-1 loop -- init only in range of source data array

      mem_v(i) := init(i);

    end loop; -- i

    return mem_v;

  end function init_boot_rom;

  -- local signals --

  signal acc_en : std_ulogic;

  signal rden   : std_ulogic;

  signal rdata  : std_ulogic_vector(31 downto 0);

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

  -- bootloader image --

  constant boot_img : boot_img_t := init_boot_rom(bootloader_init_image);

begin

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

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

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

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

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

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

  mem_file_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      rden <= rden_i and acc_en;

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

        rdata <= boot_img(to_integer(unsigned(addr)));

      end if;

    end if;

  end process mem_file_access;

  -- output gate --

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

  ack_o  <= rden;

end neorv32_boot_rom_rtl;