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-- Synthesizable MPU -- CPU + cache + bootstrap ROM (BRAM) + UART

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-- Copyright (C) 2011 Jose A. Ruiz

--                                                              

-- This source file may be used and distributed without         

-- restriction provided that this copyright statement is not    

-- removed from the file and that any derivative work contains  

-- the original copyright notice and the associated disclaimer. 

--                                                              

-- This source file 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.                                               

--                                                              

-- This source 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 this source; if not, download it   

-- from http://www.opencores.org/lgpl.shtml

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

use work.mips_pkg.all;

use work.code_rom_pkg.all;

entity mips_mpu is

    generic (

        CLOCK_FREQ     : integer := 50000000;

        SRAM_ADDR_SIZE : integer := 17

    );

    port(

        clk             : in std_logic;

        reset           : in std_logic;

        interrupt       : in std_logic_vector(7 downto 0);

        -- interface to FPGA i/o devices

        io_rd_data      : in std_logic_vector(31 downto 0);

        io_rd_addr      : out std_logic_vector(31 downto 2);

        io_wr_addr      : out std_logic_vector(31 downto 2);

        io_wr_data      : out std_logic_vector(31 downto 0);

        io_rd_vma       : out std_logic;

        io_byte_we      : out std_logic_vector(3 downto 0);

        -- interface to asynchronous 16-bit-wide EXTERNAL SRAM

        sram_address    : out std_logic_vector(SRAM_ADDR_SIZE downto 1);

        sram_data_wr    : out std_logic_vector(15 downto 0);

        sram_data_rd    : in std_logic_vector(15 downto 0);

        sram_byte_we_n  : out std_logic_vector(1 downto 0);

        sram_oe_n       : out std_logic;

        -- UART 

        uart_rxd        : in std_logic;

        uart_txd        : out std_logic;

        -- Debug info

        debug_info      : out t_debug_info

    );

end; --entity mips_mpu

architecture rtl of mips_mpu is

-- interface cpu-cache

signal cpu_data_addr :      t_word;

signal cpu_data_rd_vma :    std_logic;

signal cpu_data_rd :        t_word;

signal cpu_code_rd_addr :   t_pc;

signal cpu_code_rd :        t_word;

signal cpu_code_rd_vma :    std_logic;

signal cpu_data_wr :        t_word;

signal cpu_byte_we :        std_logic_vector(3 downto 0);

signal cpu_mem_wait :       std_logic;

signal cpu_ic_invalidate :  std_logic;

signal cpu_cache_enable :   std_logic;

signal unmapped_access :    std_logic;

-- interface to i/o

signal mpu_io_rd_data :     std_logic_vector(31 downto 0);

signal mpu_io_wr_data :     std_logic_vector(31 downto 0);

signal mpu_io_rd_addr :     std_logic_vector(31 downto 2);

signal mpu_io_wr_addr :     std_logic_vector(31 downto 2);

signal mpu_io_rd_vma :      std_logic;

signal mpu_io_byte_we :     std_logic_vector(3 downto 0);

-- interface to UARTs

signal uart_rd_word :       t_word;

signal uart_tx_rdy :        std_logic := '1';

signal uart_rx_rdy :        std_logic := '1';

signal uart_write :         std_logic;

signal uart_read :          std_logic;

signal uart_read_rx :       std_logic;

signal uart_data_rx :       std_logic_vector(7 downto 0);

-- interface to bootstrap code BRAM

-- NOTE: 'write' signals are a remnant from a previous version, to be removed

signal bram_rd_addr :       t_bram_address;

signal bram_wr_addr :       t_bram_address;

signal bram_rd_data :       t_word;

signal bram_wr_data :       t_word;

signal bram_byte_we :       std_logic_vector(3 downto 0);

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

begin

cpu: entity work.mips_cpu

    port map (

        interrupt   => interrupt,

        data_addr   => cpu_data_addr,

        data_rd_vma => cpu_data_rd_vma,

        data_rd     => cpu_data_rd,

        code_rd_addr=> cpu_code_rd_addr,

        code_rd     => cpu_code_rd,

        code_rd_vma => cpu_code_rd_vma,

        data_wr     => cpu_data_wr,

        byte_we     => cpu_byte_we,

        mem_wait    => cpu_mem_wait,

        cache_enable=> cpu_cache_enable,

        ic_invalidate=>cpu_ic_invalidate,

        clk         => clk,

        reset       => reset

    );

cache: entity work.mips_cache

    generic map (

        BRAM_ADDR_SIZE => CODE_BRAM_ADDR_SIZE,

        SRAM_ADDR_SIZE => SRAM_ADDR_SIZE

    )

    port map (

        clk             => clk,

        reset           => reset,

        -- Interface to CPU core

        data_addr       => cpu_data_addr,

        data_rd         => cpu_data_rd,

        data_rd_vma     => cpu_data_rd_vma,

        code_rd_addr    => cpu_code_rd_addr,

        code_rd         => cpu_code_rd,

        code_rd_vma     => cpu_code_rd_vma,

        byte_we         => cpu_byte_we,

        data_wr         => cpu_data_wr,

        mem_wait        => cpu_mem_wait,

        cache_enable    => cpu_cache_enable,

        ic_invalidate   => cpu_ic_invalidate,

        unmapped        => unmapped_access,

        -- interface to FPGA i/o devices

        io_rd_data      => mpu_io_rd_data,

        io_wr_data      => mpu_io_wr_data,

        io_rd_addr      => mpu_io_rd_addr,

        io_wr_addr      => mpu_io_wr_addr,

        io_rd_vma       => mpu_io_rd_vma,

        io_byte_we      => mpu_io_byte_we,

        -- interface to synchronous 32-bit-wide FPGA BRAM

        bram_rd_data    => bram_rd_data,

        bram_wr_data    => bram_wr_data,

        bram_rd_addr    => bram_rd_addr,

        bram_wr_addr    => bram_wr_addr,

        bram_byte_we    => bram_byte_we,

        -- interface to asynchronous 16-bit-wide external SRAM

        sram_address    => sram_address,

        sram_data_rd    => sram_data_rd,

        sram_data_wr    => sram_data_wr,

        sram_byte_we_n  => sram_byte_we_n,

        sram_oe_n       => sram_oe_n

    );

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

-- BRAM interface 

fpga_ram_block:

process(clk)

begin

    if clk'event and clk='1' then

        bram_rd_data <= code_bram(conv_integer(unsigned(bram_rd_addr)));

    end if;

end process fpga_ram_block;

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

-- Debug stuff

-- Register some debug signals. These are meant to be connected to LEDs on a 

-- dev board, or maybe to logic analyzer probes. They are not useful once

-- the core is fully debugged.

debug_info_register:

process(clk)

begin

    if clk'event and clk='1' then

        if reset='1' then

            debug_info.unmapped_access <= '0';

        else

            if unmapped_access='1' then

                -- This flag will be asserted permanently after any kind of 

                -- unmapped access (code, data read or data write).

                debug_info.unmapped_access <= '1';

            end if;

        end if;

        debug_info.cache_enabled <= cpu_cache_enable;

    end if;

end process debug_info_register;

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

serial_rx : entity work.rs232_rx

    generic map (

        CLOCK_FREQ => CLOCK_FREQ

    )

    port map(

        rxd =>      uart_rxd,

        data_rx =>  uart_data_rx,

        rx_rdy =>   uart_rx_rdy,

        read_rx =>  uart_read_rx,

        clk =>      clk,

        reset =>    reset

    );

-- '1'-> Read some UART register (0x2---0---)

uart_read <= '1'

    when mpu_io_rd_vma='1' and

         mpu_io_rd_addr(31 downto 28)=X"2" and

         mpu_io_rd_addr(15 downto 12)=X"0"

    else '0';

-- '1'-> Read UART Rx data (0x2---0-0-)

-- (This signal clears the RX 1-char buffer)

uart_read_rx <= '1'

    when uart_read='1' and

         mpu_io_rd_addr( 7 downto  4)=X"0"

    else '0';

-- '1'-> Write UART Tx register (trigger UART Tx)  (0x20000000)

uart_write <= '1'

    when mpu_io_byte_we/="0000" and

         mpu_io_wr_addr(31 downto 28)=X"2" and

         mpu_io_wr_addr(15 downto 12)=X"0"

    else '0';

serial_tx : entity work.rs232_tx

    generic map (

        CLOCK_FREQ => CLOCK_FREQ

    )

    port map(

        clk =>      clk,

        reset =>    reset,

        rdy =>      uart_tx_rdy,

        load =>     uart_write,

        data_i =>   mpu_io_wr_data(7 downto 0),

        txd =>      uart_txd

    );

-- Both UART rd addresses 000 and 020 read the same word (save a mux), but only

-- address 000 clears the rx buffer.

uart_rd_word <= uart_data_rx & X"00000" & "00" & uart_tx_rdy & uart_rx_rdy;

-- IO Rd mux: either the UART data/status word od the IO coming from outside

mpu_io_rd_data <=

    uart_rd_word when mpu_io_rd_addr(15 downto 12)=X"0" else

    io_rd_data;

-- io_rd_data 

io_rd_addr <= mpu_io_rd_addr;

io_wr_addr <= mpu_io_wr_addr;

io_wr_data <= mpu_io_wr_data;

io_rd_vma <= mpu_io_rd_vma;

io_byte_we <= mpu_io_byte_we;

end architecture rtl;