Subversion Repositories minimips

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

--                                                                                --

--    Copyright (c) 2004, Hangouet Samuel                                         --

--                  , Jan Sebastien                                               --

--                  , Mouton Louis-Marie                                          --

--                  , Schneider Olivier     all rights reserved                   --

--                                                                                --

--    This file is part of miniMIPS.                                              --

--                                                                                --

--    miniMIPS is free software; you can redistribute it and/or modify            --

--    it under the terms of the GNU Lesser General Public License as published by --

--    the Free Software Foundation; either version 2.1 of the License, or         --

--    (at your option) any later version.                                         --

--                                                                                --

--    miniMIPS is distributed in the hope that it will be useful,                 --

--    but WITHOUT ANY WARRANTY; without even the implied warranty of              --

--    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               --

--    GNU Lesser General Public License for more details.                         --

--                                                                                --

--    You should have received a copy of the GNU Lesser General Public License    --

--    along with miniMIPS; if not, write to the Free Software                     --

--    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA   --

--                                                                                --

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

-- If you encountered any problem, please contact :

--

--   lmouton@enserg.fr

--   oschneid@enserg.fr

--   shangoue@enserg.fr

--

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

--                                                                      --

--                                                                      --

--             miniMIPS Processor : bus controler                       --

--                                                                      --

--                                                                      --

--                                                                      --

-- Authors : Hangouet  Samuel                                           --

--           Jan       Sébastien                                        --

--           Mouton    Louis-Marie                                      --

--           Schneider Olivier                                          --

--                                                                      --

--                                                          june 2003   --

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library work;

use work.pack_mips.all;

entity bus_ctrl is

port

(

    clock : std_logic;

    reset : std_logic;

    -- Interruption in the pipeline

    interrupt      : in std_logic;

    -- Interface for the Instruction Extraction Stage

    adr_from_ei    : in bus32;      -- The address of the data to read

    instr_to_ei    : out bus32;     -- Instruction from the memory

    -- Interface with the MEMory Stage

    req_from_mem   : in std_logic;  -- Request to access the ram

    r_w_from_mem   : in std_logic;  -- Read/Write request

    adr_from_mem   : in bus32;      -- Address in ram

    data_from_mem  : in bus32;      -- Data to write in ram

    data_to_mem    : out bus32;     -- Data from the ram to the MEMory stage

    -- RAM interface signals

    req_to_ram     : out std_logic;  -- Request to ram

    adr_to_ram     : out bus32;     -- Address of the data to read or write

    r_w_to_ram     : out std_logic; -- Read/Write request

    ack_from_ram   : in std_logic;  -- Acknowledge from the memory

    data_inout_ram : inout bus32;   -- Data from/to the memory

    -- Pipeline progress control signal

    stop_all       : out std_logic

);

end bus_ctrl;

architecture rtl of bus_ctrl is

    type ctrl_state is ( ST1, ST2 );

    signal cs, ns : ctrl_state;

    signal ei_buffer : bus32;       -- Buffer storing the data for EI

    signal r_w : std_logic;         -- Current utilisation of the tristate bus

    signal data_in : bus32;         -- Data read on the tristate bus

    signal req_allowed : std_logic;

begin

    -- Read/write on the tristate bus

    process (r_w, data_from_mem, data_inout_ram)

    begin

        r_w_to_ram <= r_w;

        if r_w='0' then -- Reads bus

            data_inout_ram <= (others => 'Z');

            data_in <= data_inout_ram;

        else            -- Writing of the data from the MEM stage

            data_inout_ram <= data_from_mem;

            data_in <= (others => '0');

        end if;

    end process;

    process (clock)

    begin

        if clock='1' and clock'event then

            if reset='1' then

                cs <= ST1;

                ei_buffer <= (others => '0');

            else

                if cs=ST1 then

                    -- Storing of the data to send to EI stage

                    ei_buffer <= data_in;

                end if;

                cs <= ns;

            end if;

        end if;

    end process;

    process (clock, ack_from_ram)

    begin

        if ack_from_ram = '0' then

            req_allowed <= '0';

        elsif clock='1' and clock'event then

            if ack_from_ram = '1' then

                req_allowed <= '1';

            end if;

        end if;

    end process;

    process (req_allowed, ack_from_ram)

    begin

        if req_allowed = '1' then

            req_to_ram <= '1';

        elsif ack_from_ram = '0' then

            req_to_ram <= '1';

        else

            req_to_ram <= '0';

        end if;

    end process;

    process (cs, interrupt, adr_from_ei, req_from_mem, r_w_from_mem, adr_from_mem, ack_from_ram)

    begin

        if interrupt = '1' then -- An interruption is detected

            ns <= ST1;       -- Get back to the reading request

            stop_all <= '0'; -- The pipeline is unlock for taking in account the interruption

            adr_to_ram <= adr_from_ei;

            r_w <= '0';

        else

            case cs is

                when ST1 => -- First step the reading for EI

                    adr_to_ram <= adr_from_ei;

                    r_w <= '0';

                    if ack_from_ram='1' then

                        if req_from_mem='1' then

                            -- If request from MEM, then step 2

                            ns <= ST2;

                            stop_all <= '1';

                        else

                            -- else next reading for EI

                            ns <= ST1;

                            stop_all <= '0';

                        end if;

                    else

                        -- Wait the end of the reading

                        ns <= ST1;

                        stop_all <= '1';

                    end if;

                when ST2 => -- Treat the request from the MEM stage

                    adr_to_ram <= adr_from_mem;

                    r_w <= r_w_from_mem;

                    -- Wait the acknowledge from the RAM

                    if ack_from_ram='1' then

                        ns <= ST1;

                        stop_all <= '0';

                    else

                        ns <= ST2;

                        stop_all <= '1';

                    end if;

            end case;

        end if;

    end process;

    data_to_mem <= data_in;

    instr_to_ei <= ei_buffer when cs=ST2 else data_in;

end rtl;