Subversion Repositories open8_urisc

-- Copyright (c)2020 Jeremy Seth Henry

-- All rights reserved.

--

-- Redistribution and use in source and binary forms, with or without

-- modification, are permitted provided that the following conditions are met:

--     * Redistributions of source code must retain the above copyright

--       notice, this list of conditions and the following disclaimer.

--     * 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,

--       where applicable (as part of a user interface, debugging port, etc.)

--

-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``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 JEREMY SETH HENRY 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.

--

-- VHDL Units :  o8_register_wide

-- Description:  Provides a single addressible 16-bit output register

--

-- Register Map:

-- Offset  Bitfield Description                        Read/Write

--   0x00  AAAAAAAA Registered Outputs                    (RW)

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      05/24/20 Design copied and modified from o8_register

library ieee;

  use ieee.std_logic_1164.all;

  use ieee.std_logic_unsigned.all;

  use ieee.std_logic_arith.all;

  use ieee.std_logic_misc.all;

library work;

  use work.open8_pkg.all;

entity o8_register_wide is

generic(

  Default_Reg0               : DATA_TYPE := x"00";

  Default_Reg1               : DATA_TYPE := x"00";

  Default_Reg2               : DATA_TYPE := x"00";

  Default_Reg3               : DATA_TYPE := x"00";

  Address                    : ADDRESS_TYPE

);

port(

  Open8_Bus                  : in  OPEN8_BUS_TYPE;

  Write_Qual                 : in  std_logic := '1';

  Rd_Data                    : out DATA_TYPE;

  --

  Register_0                 : out DATA_TYPE;

  Register_1                 : out DATA_TYPE;

  Register_2                 : out DATA_TYPE;

  Register_3                 : out DATA_TYPE

);

end entity;

architecture behave of o8_register_wide is

  alias Clock                is Open8_Bus.Clock;

  alias Reset                is Open8_Bus.Reset;

  constant User_Addr         : std_logic_vector(15 downto 2)

                               := Address(15 downto 2);

  alias  Comp_Addr           is Open8_Bus.Address(15 downto 2);

  signal Addr_Match          : std_logic;

  alias  Reg_Sel_d           is Open8_Bus.Address(1 downto 0);

  signal Reg_Sel_q           : std_logic_vector(1 downto 0) := "00";

  signal Wr_En_d             : std_logic := '0';

  signal Wr_En_q             : std_logic := '0';

  alias  Wr_Data_d           is Open8_Bus.Wr_Data;

  signal Wr_Data_q           : DATA_TYPE := x"00";

  signal Rd_En_d             : std_logic := '0';

  signal Rd_En_q             : std_logic := '0';

  signal Reg0_Out            : DATA_TYPE := x"00";

  signal Reg1_Out            : DATA_TYPE := x"00";

  signal Reg2_Out            : DATA_TYPE := x"00";

  signal Reg3_Out            : DATA_TYPE := x"00";

begin

  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';

  Wr_En_d                    <= Addr_Match and Open8_Bus.Wr_En;

  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Reg_Sel_q              <= "00";

      Wr_En_q                <= '0';

      Wr_Data_q              <= x"00";

      Reg0_Out               <= Default_Reg0;

      Reg1_Out               <= Default_Reg1;

      Reg2_Out               <= Default_Reg2;

      Reg3_Out               <= Default_Reg3;

      Rd_En_q                <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

    elsif( rising_edge( Clock ) )then

      Reg_Sel_q              <= Reg_Sel_d;

      Wr_En_q                <= Wr_En_d;

      Wr_Data_q              <= Wr_Data_d;

      if( Wr_En_q = '1' and Write_Qual = '1' )then

        case( Reg_Sel_q )is

          when "00" =>

            Reg0_Out         <= Wr_Data_q;

          when "01" =>

            Reg1_Out         <= Wr_Data_q;

          when "10" =>

            Reg2_Out         <= Wr_Data_q;

          when "11" =>

            Reg3_Out         <= Wr_Data_q;

          when others =>

            null;

        end case;

      end if;

      Rd_Data                <= OPEN8_NULLBUS;

      Rd_En_q                <= Rd_En_d;

      if( Rd_En_q = '1' )then

        case( Reg_Sel_q )is

          when "00" =>

            Rd_Data          <= Reg0_Out;

          when "01" =>

            Rd_Data          <= Reg1_Out;

          when "10" =>

            Rd_Data          <= Reg2_Out;

          when "11" =>

            Rd_Data          <= Reg3_Out;

          when others =>

            null;

        end case;

      end if;

    end if;

  end process;

  Register_0                 <= Reg0_Out;

  Register_1                 <= Reg1_Out;

  Register_2                 <= Reg2_Out;

  Register_3                 <= Reg3_Out;

end architecture;