Subversion Repositories neorv32

-- #################################################################################################
-- # << NEORV32 - Processor-internal bootloader ROM (BOOTROM) >>                                   #
-- # ********************************************************************************************* #
-- # BSD 3-Clause License                                                                          #
-- #                                                                                               #
-- # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #
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-- # permitted provided that the following conditions are met:                                     #
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-- #    conditions and the following disclaimer in the documentation and/or other materials        #
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-- #    permission.                                                                                #
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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;