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-- Copyright 2015, Jürgen Defurne

--

-- This file is part of the Experimental Unstable CPU System.

--

-- The Experimental Unstable CPU System 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 3 of the

-- License, or (at your option) any later version.

--

-- The Experimental Unstable CPU System 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 Experimental Unstable CPU System. If not, see

-- http://www.gnu.org/licenses/lgpl.txt.

LIBRARY ieee;

USE ieee.std_logic_1164.ALL;

USE ieee.numeric_std.ALL;

PACKAGE ram_parts IS

  COMPONENT generic_ram IS

    GENERIC (

      filename : STRING                := "";

      w_data   : NATURAL RANGE 1 TO 32 := 16;

      w_addr   : NATURAL RANGE 8 TO 14 := 10);

    PORT (

      clk : IN  STD_LOGIC;

      we  : IN  STD_LOGIC;

      a1  : IN  STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);  -- Data port address

      a2  : IN  STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);  -- Instruction port address

      d1  : IN  STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);  -- Data port input

      q1  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);  -- Data port output

      q2  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0));  -- Instruction port output

  END COMPONENT generic_ram;

  COMPONENT RAM32K IS

    GENERIC (

      w_data : NATURAL RANGE 1 TO 32 := 16;

      file_1 : STRING                := "";

      file_2 : STRING                := "";

      file_3 : STRING                := "";

      file_4 : STRING                := "");

    PORT (

      clk : IN  STD_LOGIC;

      we  : IN  STD_LOGIC;

      a1  : IN  STD_LOGIC_VECTOR(14 DOWNTO 0);  -- Data port address

      a2  : IN  STD_LOGIC_VECTOR(14 DOWNTO 0);  -- Instruction port address

      d1  : IN  STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);   -- Data port input

      q1  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);   -- Data port output

      q2  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0));  -- Instruction port output

  END COMPONENT RAM32K;

END PACKAGE ram_parts;

LIBRARY ieee;

USE ieee.std_logic_1164.ALL;

USE ieee.numeric_std.ALL;

USE std.textio.ALL;

USE ieee.std_logic_textio.ALL;

USE work.arrayio.ALL;

ENTITY generic_ram IS

  -- Memory component based upon Xilinx Spartan-6 block RAM

  -- Maximum capacity is 16k words

  -- This component can be initialised by passing a file name as a generic

  -- parameter.

  GENERIC (

    filename : STRING                := "";

    w_data   : NATURAL RANGE 1 TO 32 := 16;

    w_addr   : NATURAL RANGE 8 TO 14 := 10);

  PORT (

    clk : IN  STD_LOGIC;

    we  : IN  STD_LOGIC;

    a1  : IN  STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);  -- Data port address

    a2  : IN  STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);  -- Instruction port address

    d1  : IN  STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);  -- Data port input

    q1  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);  -- Data port output

    q2  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0));  -- Instruction port output

END generic_ram;

ARCHITECTURE Behavioral OF generic_ram IS

  SIGNAL mem : cstr_array_type(0 TO (2**w_addr) - 1) := init_cstr(2**w_addr, filename);

  SIGNAL address_reg_1 : STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);

  SIGNAL address_reg_2 : STD_LOGIC_VECTOR(w_addr - 1 DOWNTO 0);

BEGIN  -- Behavioral

  -- purpose: Try to describe a proper block ram without needing to instantiate a BRAM

  -- type   : sequential

  -- inputs : clk, we, a1, a2, d1

  -- outputs: q1, q2

  MP1 : PROCESS (clk, address_reg_1, address_reg_2, mem)

  BEGIN  -- PROCESS MP1

    -- Reading

    q1 <= STD_LOGIC_VECTOR(to_unsigned(mem(to_integer(UNSIGNED(address_reg_1))), w_data));

    q2 <= STD_LOGIC_VECTOR(to_unsigned(mem(to_integer(UNSIGNED(address_reg_2))), w_data));

    IF rising_edge(clk) THEN            -- rising clock edge

      -- These work like the block RAM registers

      address_reg_1 <= a1;

      address_reg_2 <= a2;

      -- Writing

      IF we = '1' THEN

        mem(to_integer(UNSIGNED(a1))) <= to_integer(UNSIGNED(d1));

      END IF;

    END IF;

  END PROCESS MP1;

END Behavioral;

LIBRARY ieee;

USE ieee.std_logic_1164.ALL;

USE ieee.numeric_std.ALL;

USE work.mux_parts.ALL;

USE work.ram_parts.ALL;

ENTITY RAM32K IS

  -- This component is based upon the above defined generic_ram

  -- It is constructed using a 4-to-1 multiplexer and 4 8k word

  -- generic_rams.

  -- In order to initialise it, a filename can be passed, which is then

  -- used to generate the names of four files which should have been

  -- prepared previously: filename_{0|1|2|3}.txt

  -- These will be used to initialise the four RAM components.

  GENERIC (

    w_data : NATURAL RANGE 1 TO 32 := 16;

    file_1 : STRING                := "";

    file_2 : STRING                := "";

    file_3 : STRING                := "";

    file_4 : STRING                := "");

  PORT (

    clk : IN  STD_LOGIC;

    we  : IN  STD_LOGIC;

    a1  : IN  STD_LOGIC_VECTOR(14 DOWNTO 0);  -- Data port address

    a2  : IN  STD_LOGIC_VECTOR(14 DOWNTO 0);  -- Instruction port address

    d1  : IN  STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);   -- Data port input

    q1  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);   -- Data port output

    q2  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0));  -- Instruction port output

END RAM32K;

ARCHITECTURE Structural OF RAM32K IS

  SIGNAL data_address  : STD_LOGIC_VECTOR(12 DOWNTO 0);

  SIGNAL data_select   : STD_LOGIC_VECTOR(1 DOWNTO 0);

  SIGNAL instr_address : STD_LOGIC_VECTOR(12 DOWNTO 0);

  SIGNAL instr_select  : STD_LOGIC_VECTOR(1 DOWNTO 0);

  SIGNAL wr_sel : STD_LOGIC_VECTOR(3 DOWNTO 0);

  TYPE bus_array_t IS ARRAY(0 TO 3) OF STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);

  SIGNAL data : bus_array_t;

  SIGNAL inst : bus_array_t;

  TYPE file_array IS ARRAY(INTEGER RANGE <>) OF STRING(1 TO 100);

  CONSTANT i_file : file_array(0 TO 3) := (file_1, file_2, file_3, file_4);

BEGIN  -- Structural

  data_address <= a1(12 DOWNTO 0);

  data_select  <= a1(14 DOWNTO 13);

  instr_address <= a2(12 DOWNTO 0);

  instr_select  <= a2(14 DOWNTO 13);

  wr_sel <= "0001" WHEN data_select = "00" AND we = '1' ELSE

            "0010" WHEN data_select = "01" AND we = '1' ELSE

            "0100" WHEN data_select = "10" AND we = '1' ELSE

            "1000" WHEN data_select = "11" AND we = '1' ELSE

            "0000";

  M1 : mux4to1

    PORT MAP (

      SEL => data_select,

      S0  => data(0),

      S1  => data(1),

      S2  => data(2),

      S3  => data(3),

      Y   => q1);

  M2 : mux4to1

    PORT MAP (

      SEL => instr_select,

      S0  => inst(0),

      S1  => inst(1),

      S2  => inst(2),

      S3  => inst(3),

      Y   => q2);

  RAM : FOR i IN 0 TO 3 GENERATE

    R0 : generic_ram

      GENERIC MAP (

        filename => i_file(i),

        w_data   => w_data,

        w_addr   => 13)

      PORT MAP (

        clk => clk,

        we  => wr_sel(i),

        a1  => data_address,

        a2  => instr_address,

        d1  => d1,

        q1  => data(i),

        q2  => inst(i));

  END GENERATE RAM;

END Structural;