syscop.vhd

这是一个基于mips-I结构的处理器,32bit,冯诺依曼结构

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--                                                                                --
--    Copyright (c) 2004, Hangouet Samuel                                         --
--                  , Jan Sebastien                                               --
--                  , Mouton Louis-Marie                                          --
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--------------------------------------------------------------------------
--                                                                      --
--                                                                      --
--        miniMIPS Processor : Coprocessor system (cop0)                --
--                                                                      --
--                                                                      --
--                                                                      --
-- Authors : Hangouet  Samuel                                           --
--           Jan       S閎astien                                        --
--           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;

-- By convention in the commentary, the term interruption means hardware interruptions and software exceptions

entity syscop is
port
(
    clock         : in std_logic;
    reset         : in std_logic;

    -- Datas from the pipeline
    MEM_adr       : in bus32;       -- Address of the current instruction in the pipeline end -> responsible of the exception
    MEM_exc_cause : in bus32;       -- Potential cause exception of that instruction
    MEM_it_ok     : in std_logic;   -- Allow hardware interruptions

    -- Hardware interruption
    it_mat        : in std_logic;   -- Hardware interruption detected

    -- Interruption controls
    interrupt     : out std_logic;  -- Interruption to take into account
    vecteur_it    : out bus32;      -- Interruption vector

    -- Writing request in register bank
    write_data    : in bus32;       -- Data to write
    write_adr     : in bus5;        -- Address of the register to write
    write_SCP     : in std_logic;   -- Writing request

    -- Reading request in register bank
    read_adr1     : in bus5;        -- Address of the first register
    read_adr2     : in bus5;        -- Address of the second register
    read_data1    : out bus32;      -- Value of register 1
    read_data2    : out bus32       -- Value of register 2
);
end syscop;


architecture rtl of syscop is

    subtype adr_scp_reg is integer range 12 to 15;

    type scp_reg_type is array (integer range adr_scp_reg'low to adr_scp_reg'high) of bus32;

    -- Constants to define the coprocessor registers
    constant COMMAND   : integer      := 0;   -- False register to command the coprocessor system
    constant STATUS    : adr_scp_reg  := 12;  -- Registre 12 of the coprocessor system
    constant CAUSE     : adr_scp_reg  := 13;  -- Registre 13 of the coprocessor system
    constant ADRESSE   : adr_scp_reg  := 14;  -- Registre 14 of the coprocessor system
    constant VECTIT    : adr_scp_reg  := 15;  -- Registre 15 of the coprocessor system

    signal scp_reg : scp_reg_type;          -- Internal register bank
    signal pre_reg : scp_reg_type;          -- Register bank preparation

    signal adr_src1 : integer range 0 to 31;
    signal adr_src2 : integer range 0 to 31;
    signal adr_dest : integer range 0 to 31;

    signal exception : std_logic;           -- Set to '1' when exception detected
    signal interruption : std_logic;        -- Set to '1' when interruption detected
    signal cmd_itret    : std_logic;        -- Set to '1' when interruption return command is detected

    signal save_msk  : std_logic;           -- Save the mask state when an interruption occurs

begin

    -- Detection of the interruptions
    exception <= '1' when MEM_exc_cause/=IT_NOEXC else '0';
    interruption <= '1' when it_mat='1' and scp_reg(STATUS)(0)='1' and MEM_it_ok='1' else '0';

    -- Update asynchronous outputs
    interrupt <= exception or interruption; -- Detection of interruptions
    vecteur_it <= scp_reg(ADRESSE) when cmd_itret = '1' else -- Send the return adress when a return instruction appears
                  scp_reg(VECTIT);                           -- Send the interruption vector in other cases


    -- Decode the address of the registers
    adr_src1 <= to_integer(unsigned(read_adr1));
    adr_src2 <= to_integer(unsigned(read_adr2));
    adr_dest <= to_integer(unsigned(write_adr));

    -- Read the two registers
    read_data1 <= (others => '0') when (adr_src1<scp_reg'low or adr_src1>scp_reg'high) else
                  scp_reg(adr_src1);
    read_data2 <= (others => '0') when adr_src2<scp_reg'low or adr_src2>scp_reg'high else
                  scp_reg(adr_src2);

    -- Define the pre_reg signal, next value for the registers
    process (scp_reg, adr_dest, write_SCP, write_data, interruption,
             exception, MEM_exc_cause, MEM_adr, reset)
    begin
        pre_reg <= scp_reg;
        cmd_itret <= '0'; -- No IT return in most cases

        -- Potential writing in a register
        if (write_SCP='1' and adr_dest>=pre_reg'low and adr_dest<=pre_reg'high) then
            pre_reg(adr_dest) <= write_data;
        end if;

        -- Command from the core
        if write_SCP='1' and adr_dest=COMMAND then
            case write_data is -- Different operations
                when SYS_UNMASK => pre_reg(STATUS)(0) <= '1'; -- Unamsk command
                when SYS_MASK   => pre_reg(STATUS)(0) <= '0'; -- Mask command
                when SYS_ITRET  => -- Interruption return command
                                   pre_reg(STATUS)(0) <= save_msk; -- Restore the mask before the interruption
                                   cmd_itret          <= '1';      -- False interruption request (to clear the pipeline)
                when others     => null;
            end case;
        end if;

        -- Modifications from the interruptions
        if interruption='1' then
            pre_reg(STATUS)(0) <= '0';       -- Mask the interruptions
            pre_reg(CAUSE) <= IT_ITMAT;      -- Save the interruption cause
            pre_reg(ADRESSE) <= MEM_adr;     -- Save the return address
        end if;

        -- Modifications from the exceptions
        if exception='1' then
            pre_reg(STATUS)(0) <= '0';       -- Mask the interruptions
            pre_reg(CAUSE) <= MEM_exc_cause; -- Save the exception cause
            pre_reg(ADRESSE) <= MEM_adr;     -- Save the return address
        end if;

        -- The reset has the priority on the other cuases
        if reset='1' then
            pre_reg <= (others => (others => '0'));
            -- NB : The processor is masked after a reset
            --      The exception handler is set at address 0
        end if;
    end process;

    -- Memorisation of the modifications in the register bank
    process(clock)
    begin
        if clock='1' and clock'event then

            -- Save the mask when an interruption appears
            if (exception='1') or (interruption='1') then
                save_msk <= scp_reg(STATUS)(0);
            end if;

            scp_reg <= pre_reg;
            
        end if;
    end process;

end rtl;