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 or 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)

    -- Internal instruction memory --

    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

    -- Internal data memory --

    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

    cancel_i : in  std_ulogic; -- cancel current bus transaction

    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                    : std_ulogic;

  signal wb_access                       : std_ulogic;

  signal wb_access_ff, wb_access_ff_ff   : std_ulogic;

  signal rb_en                           : 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;

  -- data read-back --

  signal wb_rdata : std_ulogic_vector(31 downto 0);

begin

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

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

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

  assert (INTERFACE_REG_STAGES /= 0) report "NEORV32 CONFIG WARNING! External memory interface without register stages is still experimental for peripherals with more than 1 cycle latency." severity warning;

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

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

  -- access to internal IMEM or DMEM? --

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

  int_dmem_acc <= '1' when (addr_i >= dmem_base_c) and (addr_i < std_ulogic_vector(unsigned(dmem_base_c) + 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_rom_base_c) else '0'; -- this also covers access to the IO space

--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 (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';

      wb_access_ff    <= '0';

      wb_access_ff_ff <= '0';

    elsif rising_edge(clk_i) then

      -- bus cycle --

      if (INTERFACE_REG_STAGES = 0) then

        wb_cyc_ff <= '0'; -- unused

      else

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

      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;

      -- access still active? --

      wb_access_ff_ff <= wb_access_ff;

      if (wb_access = '1') then

        wb_access_ff <= '1';

      elsif ((wb_ack_i or wb_err_i or cancel_i) = '1') then

        wb_access_ff <= '0';

      end if;

    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;

  -- cpu read-data --

  rb_en  <= wb_access_ff_ff when (INTERFACE_REG_STAGES = 2) else wb_access_ff;

  data_o <= wb_rdata when (rb_en = '1') else (others => '0');

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

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

  interface_reg_level_zero:

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

    wb_rdata <= 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

        if (wb_cyc_ff = '0') then

          wb_adr_o <= addr_i;

          wb_dat_o <= data_i;

          wb_sel_o <= ben_i;

          wb_we_o  <= wren_i;

        end if;

      end if;

    end process buffer_stages_one;

    wb_rdata <= 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

        if (wb_cyc_ff = '0') then

          wb_adr_o <= addr_i;

          wb_dat_o <= data_i;

          wb_sel_o <= ben_i;

          wb_we_o  <= wren_i;

        end if;

        if (wb_ack_i = '1') then

          wb_rdata <= wb_dat_i;

        end if;

      end if;

    end process buffer_stages_two;

  end generate;

end neorv32_wishbone_rtl;