Subversion Repositories neorv32

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

-- # << NEORV32 - External Bus Interface (WISHBONE) >>                                             #

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

-- # The interface is either unregistered (INTERFACE_REG_STAGES = 0), only outgoing signals are    #

-- # registered (INTERFACE_REG_STAGES = 1) or incoming and outgoing signals are registered         #

-- # (INTERFACE_REG_STAGES = 2).                                                                   #

-- #                                                                                               #

-- # All bus accesses from the CPU, which do not target the internal IO region, the internal boot- #

-- # loader or the internal instruction & data memories (if implemented), are delegated via this   #

-- # Wishbone gateway to the external bus interface.                                               #

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

-- # 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_wishbone is

  generic (

    INTERFACE_REG_STAGES : natural := 2; -- number of interface register stages (0,1,2)

    -- Memory configuration: Instruction memory --

    MEM_ISPACE_BASE      : std_ulogic_vector(31 downto 0) := x"00000000"; -- base address of instruction memory space

    MEM_ISPACE_SIZE      : natural := 8*1024; -- total size of instruction memory space in byte

    MEM_INT_IMEM_USE     : boolean := true;   -- implement processor-internal instruction memory

    MEM_INT_IMEM_SIZE    : natural := 8*1024; -- size of processor-internal instruction memory in bytes

    -- Memory configuration: Data memory --

    MEM_DSPACE_BASE      : std_ulogic_vector(31 downto 0) := x"80000000"; -- base address of data memory space

    MEM_DSPACE_SIZE      : natural := 4*1024; -- total size of data memory space in byte

    MEM_INT_DMEM_USE     : boolean := true;   -- implement processor-internal data memory

    MEM_INT_DMEM_SIZE    : natural := 4*1024  -- size of processor-internal data memory in bytes

  );

  port (

    -- global control --

    clk_i    : in  std_ulogic; -- global clock line

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

    -- host access --

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

    rden_i   : in  std_ulogic; -- read enable

    wren_i   : in  std_ulogic; -- write enable

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

    data_i   : in  std_ulogic_vector(31 downto 0); -- data in

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

    ack_o    : out std_ulogic; -- transfer acknowledge

    err_o    : out std_ulogic; -- transfer error

    -- wishbone interface --

    wb_adr_o : out std_ulogic_vector(31 downto 0); -- address

    wb_dat_i : in  std_ulogic_vector(31 downto 0); -- read data

    wb_dat_o : out std_ulogic_vector(31 downto 0); -- write data

    wb_we_o  : out std_ulogic; -- read/write

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

    wb_stb_o : out std_ulogic; -- strobe

    wb_cyc_o : out std_ulogic; -- valid cycle

    wb_ack_i : in  std_ulogic; -- transfer acknowledge

    wb_err_i : in  std_ulogic  -- transfer error

  );

end neorv32_wishbone;

architecture neorv32_wishbone_rtl of neorv32_wishbone is

  -- access control --

  signal int_imem_acc, int_imem_acc_real : std_ulogic;

  signal int_dmem_acc, int_dmem_acc_real : std_ulogic;

  signal int_boot_acc, int_io_acc        : std_ulogic;

  signal wb_access                       : std_ulogic;

  -- bus arbiter --

  signal wb_stb_ff0 : std_ulogic;

  signal wb_stb_ff1 : std_ulogic;

  signal wb_cyc_ff  : std_ulogic;

  signal wb_ack_ff  : std_ulogic;

  signal wb_err_ff  : std_ulogic;

begin

  -- Sanity Check ---------------------------------------------------------------------------

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

  sanity_check: process(clk_i)

  begin

    if rising_edge(clk_i) then -- just for simulation

      if (INTERFACE_REG_STAGES > 2) then

        assert false report "NEORV32 CONFIG ERROR! Number of external memory interface buffer stages must be 0, 1 or 2." severity error;

      end if;

    end if;

  end process sanity_check;

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

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

  -- access to internal IMEM or DMEM? --

  int_imem_acc <= '1' when (addr_i >= MEM_ISPACE_BASE) and (addr_i < std_ulogic_vector(unsigned(MEM_ISPACE_BASE) + MEM_INT_IMEM_SIZE)) else '0';

  int_dmem_acc <= '1' when (addr_i >= MEM_DSPACE_BASE) and (addr_i < std_ulogic_vector(unsigned(MEM_DSPACE_BASE) + MEM_INT_DMEM_SIZE)) else '0';

  int_imem_acc_real <= int_imem_acc when (MEM_INT_IMEM_USE = true) else '0';

  int_dmem_acc_real <= int_dmem_acc when (MEM_INT_DMEM_USE = true) else '0';

  int_boot_acc <= '1' when (addr_i >= boot_base_c) else '0';

  int_io_acc   <= '1' when (addr_i >= io_base_c)   else '0';

  -- actual external bus access? --

  wb_access <= (not int_imem_acc_real) and (not int_dmem_acc_real) and (not int_boot_acc) and (not int_io_acc) and (wren_i or rden_i);

  -- Bus Arbiter -----------------------------------------------------------------------------

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

  bus_arbiter: process(rstn_i, clk_i)

  begin

    if (rstn_i = '0') then

      wb_cyc_ff  <= '0';

      wb_stb_ff1 <= '0';

      wb_stb_ff0 <= '0';

      wb_ack_ff  <= '0';

      wb_err_ff  <= '0';

    elsif rising_edge(clk_i) then

      -- bus cycle --

      if (INTERFACE_REG_STAGES = 0) then

        wb_cyc_ff <= '0'; -- unused

      elsif (INTERFACE_REG_STAGES = 1) then

        wb_cyc_ff <= wb_access and ((not wb_ack_i) or (not wb_err_i));

      elsif (INTERFACE_REG_STAGES = 2) then

        wb_cyc_ff <= wb_access and ((not wb_ack_ff) or (not wb_err_ff));

      end if;

      -- bus strobe --

      wb_stb_ff1 <= wb_stb_ff0;

      wb_stb_ff0 <= wb_access;

      -- bus ack --

      wb_ack_ff <= wb_ack_i;

      -- bus err --

      wb_err_ff <= wb_err_i;

    end if;

  end process bus_arbiter;

  -- bus cycle --

  wb_cyc_o <= wb_access when (INTERFACE_REG_STAGES = 0) else wb_cyc_ff;

  -- bus_strobe: rising edge detector --

  wb_stb_o <= (wb_access and (not wb_stb_ff0)) when (INTERFACE_REG_STAGES = 0) else (wb_stb_ff0 and (not wb_stb_ff1));

  -- cpu ack --

  ack_o <= wb_ack_ff when (INTERFACE_REG_STAGES = 2) else wb_ack_i;

  -- cpu err --

  err_o <= wb_err_ff when (INTERFACE_REG_STAGES = 2) else wb_err_i;

  -- Bus Buffer -----------------------------------------------------------------------------

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

  interface_reg_level_zero:

  if (INTERFACE_REG_STAGES = 0) generate -- 0 register levels: direct connection

    data_o   <= wb_dat_i;

    wb_adr_o <= addr_i;

    wb_dat_o <= data_i;

    wb_sel_o <= ben_i;

    wb_we_o  <= wren_i;

  end generate;

  interface_reg_level_one:

  if (INTERFACE_REG_STAGES = 1) generate -- 1 register levels: buffer outgoing signals

    buffer_stages_one: process(clk_i)

    begin

      if rising_edge(clk_i) then

        wb_adr_o <= addr_i;

        wb_dat_o <= data_i;

        wb_sel_o <= ben_i;

        wb_we_o  <= wren_i;

      end if;

    end process buffer_stages_one;

    data_o <= wb_dat_i;

  end generate;

  interface_reg_level_two:

  if (INTERFACE_REG_STAGES = 2) generate -- 2 register levels: buffer incoming and outgoing signals

    buffer_stages_two: process(clk_i)

    begin

      if rising_edge(clk_i) then

        wb_adr_o <= addr_i;

        wb_dat_o <= data_i;

        wb_sel_o <= ben_i;

        wb_we_o  <= wren_i;

        data_o   <= wb_dat_i;

      end if;

    end process buffer_stages_two;

  end generate;

end neorv32_wishbone_rtl;