Subversion Repositories neorv32

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

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

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

-- # The interface provides registers for all outgoing signals. If the host cancels a running      #

-- # transfer, the Wishbone arbiter still waits some time for the bus system to ACK to transfer.   #

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

-- # 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.                                               #

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

-- # This interface supports classic/standard Wishbone transactions (WB_PIPELINED_MODE = false)    #

-- # and also pipelined transactions (WB_PIPELINED_MODE = true).                                   #

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

-- # 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 (

    WB_PIPELINED_MODE : boolean := false; -- false: classic/standard wishbone mode, true: pipelined wishbone mode

    -- 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

  -- constants --

  constant wb_timeout_c : natural := bus_timeout_c/2;

  -- 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;

  -- bus arbiter

  type ctrl_state_t is (IDLE, BUSY, CANCELED);

  type ctrl_t is record

    state      : ctrl_state_t;

    state_prev : ctrl_state_t;

    we         : std_ulogic;

    rd_req     : std_ulogic;

    wr_req     : std_ulogic;

    adr        : std_ulogic_vector(31 downto 0);

    wdat       : std_ulogic_vector(31 downto 0);

    rdat       : std_ulogic_vector(31 downto 0);

    sel        : std_ulogic_vector(3 downto 0);

    ack        : std_ulogic;

    err        : std_ulogic;

    timeout    : std_ulogic_vector(index_size_f(wb_timeout_c)-1 downto 0);

  end record;

  signal ctrl : ctrl_t;

  signal stb_int, cyc_int : std_ulogic;

begin

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

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

  assert not (bus_timeout_c <= 15) report "NEORV32 PROCESSOR CONFIG ERROR: Bus timeout (bus_timeout_c) should be >16 for interfacing external modules." severity error;

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

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

  -- access to internal IMEM or DMEM? --

  int_imem_acc <= '1' when (addr_i(31 downto index_size_f(MEM_INT_IMEM_SIZE)) = imem_base_c(31 downto index_size_f(MEM_INT_IMEM_SIZE))) else '0';

  int_dmem_acc <= '1' when (addr_i(31 downto index_size_f(MEM_INT_DMEM_SIZE)) = dmem_base_c(31 downto index_size_f(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';

  -- access to internal BOOTROM or IO devices? --

  int_boot_acc <= '1' when (addr_i >= boot_rom_base_c) else '0'; -- this also covers access to the IO space

--int_boot_acc <= '1' when (addr_i(31 downto index_size_f(2*boot_rom_max_size_c)) = boot_rom_base_c(31 downto index_size_f(2*boot_rom_max_size_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);

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

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

  bus_arbiter: process(rstn_i, clk_i)

  begin

    if (rstn_i = '0') then

      ctrl.state      <= IDLE;

      ctrl.state_prev <= IDLE;

      ctrl.we         <= '0';

      ctrl.rd_req     <= '0';

      ctrl.wr_req     <= '0';

      ctrl.adr        <= (others => '0');

      ctrl.wdat       <= (others => '0');

      ctrl.rdat       <= (others => '0');

      ctrl.sel        <= (others => '0');

      ctrl.timeout    <= (others => '0');

      ctrl.ack        <= '0';

      ctrl.err        <= '0';

    elsif rising_edge(clk_i) then

      -- defaults --

      ctrl.state_prev <= ctrl.state;

      ctrl.rdat       <= (others => '0');

      ctrl.ack        <= '0';

      ctrl.err        <= '0';

      ctrl.timeout    <= std_ulogic_vector(to_unsigned(wb_timeout_c, index_size_f(wb_timeout_c)));

      -- state machine --

      case ctrl.state is

        when IDLE => -- waiting for host request

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

          ctrl.rd_req <= '0';

          ctrl.wr_req <= '0';

          -- buffer all outgoing signals --

          ctrl.we   <= wren_i;

          ctrl.adr  <= addr_i;

          ctrl.wdat <= data_i;

          ctrl.sel  <= ben_i;

          -- valid read/write access --

          if ((wb_access and (wren_i or ctrl.wr_req or rden_i or ctrl.rd_req)) = '1') then

            ctrl.state <= BUSY;

          end if;

        when BUSY => -- transfer in progress

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

          ctrl.rdat <= wb_dat_i;

          if (cancel_i = '1') then -- transfer canceled by host

            ctrl.state <= CANCELED;

          elsif (wb_err_i = '1') then -- abnormal bus termination

            ctrl.err   <= '1';

            ctrl.state <= CANCELED;

          elsif (wb_ack_i = '1') then -- normal bus termination

            ctrl.ack   <= '1';

            ctrl.state <= IDLE;

          end if;

        when CANCELED => -- 

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

          ctrl.wr_req <= ctrl.wr_req or wren_i; -- buffer new request

          ctrl.rd_req <= ctrl.rd_req or rden_i; -- buffer new request

          -- wait for bus.peripheral to ACK transfer (as "aborted" but still somehow "completed")

          -- or wait for a timeout and force termination

          ctrl.timeout <= std_ulogic_vector(unsigned(ctrl.timeout) - 1); -- timeout counter

          if (wb_ack_i = '1') or (or_all_f(ctrl.timeout) = '0') then

            ctrl.state <= IDLE;

          end if;

        when others => -- undefined

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

          ctrl.state <= IDLE;

      end case;

    end if;

  end process bus_arbiter;

  -- host access --

  data_o   <= ctrl.rdat;

  ack_o    <= ctrl.ack;

  err_o    <= ctrl.err;

  -- wishbone interface --

  wb_adr_o <= ctrl.adr;

  wb_dat_o <= ctrl.wdat;

  wb_we_o  <= ctrl.we;

  wb_sel_o <= ctrl.sel;

  wb_stb_o <= stb_int when (WB_PIPELINED_MODE = true) else cyc_int;

  wb_cyc_o <= cyc_int;

  stb_int  <= '1' when ((ctrl.state = BUSY) and (ctrl.state_prev = IDLE)) else '0';

  cyc_int  <= '0' when (ctrl.state = IDLE) else '1';

end neorv32_wishbone_rtl;