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--===========================================================================--

--                                                                           --

--  xula_ioport.vhd - Synthesizable Dual Bidirectionsal I/O Port             --

--                                                                           --

--===========================================================================--

--

--  File name      : xula_ioport.vhd

--

--  Purpose        : Implements a dual 8 bit bidirectional I/O port

--                   modified for the XuLA implementation of System09

--                   Port A supports a full 8 bit bidirectional port

--                   Port B supports a 5 bit bidirectional port with 3 inputs 

-- 

--  Dependencies   : ieee.std_logic_1164

--                   ieee.std_logic_unsigned

--                   unisim.vcomponents

--

--  Author         : John E. Kent

--

--  Email          : dilbert57@opencores.org      

--

--  Web            : http://opencores.org/project,system09

--

--  xula_ioport.vhd is a dual bi-directional 8 bit I/O port written in VHDL.

--

--  address  function

--  =======  ========

--  base+0   port a data register

--           bits 0 - 7 = i/o

--  base+1   port b data register

--           bits 0 - 4 = i/o

--           bits 5 - 7 - inputs

--  base+2   port a direction register 

--           0 => port a bit = input

--           1 => port a bit = output

--  base+3   port b direction

--           For bits 0 to 4:

--           0 => port b bit = input

--           1 => port b bit = output

--           For bits 5 to 7:

--           0 => port b bit = interrupt disable

--           1 => port b bit = interrupt enable

--           interrupt inputs on port b bits 5 to 7 are active high

--

--  Copyright (C) 2002 - 2011 John Kent

--

--  This program is free software: you can redistribute it and/or modify

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

--  the Free Software Foundation, either version 3 of the License, or

--  (at your option) any later version.

--

--  This program 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 General Public License for more details.

--

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

--  along with this program.  If not, see <http://www.gnu.org/licenses/>.

--

--===========================================================================--

--                                                                           --

--                              Revision  History                            --

--                                                                           --

--===========================================================================--

--

-- Version  Author        Date               Description

-- 0.1      John E. Kent  11 October 2002    Used a loop counter for 

--                                           data direction & read port signals

-- 0.2      John E. Kent  5 September 2003   Reduced to 2 x 8 bit ports

-- 1.0      John E. Kent  6 September 2003   Changed Clock Edge

-- 1.1      John E. Kent  25 Februrary 2007  Modified sensitivity lists

-- 1.2      John E. Kent  30 May 2010        Updated Header, added unisim library

-- 2.0      John E. Kent  30 April 2011      modified for XuLA System09 I/O

--===========================================================================

--

library ieee;

  use ieee.std_logic_1164.all;

  use ieee.std_logic_unsigned.all;

--library unisim;

--  use unisim.vcomponents.all;

entity xula_ioport is

  port (

    clk       : in    std_logic;

    rst       : in    std_logic;

    cs        : in    std_logic;

    rw        : in    std_logic;

    addr      : in    std_logic_vector(1 downto 0);

    data_in   : in    std_logic_vector(7 downto 0);

    data_out  : out   std_logic_vector(7 downto 0);

    porta_io  : inout std_logic_vector(7 downto 0);

    portb_io  : inout std_logic_vector(4 downto 0);

    portc_in  : in    std_logic_vector(7 downto 5);

    irq       : out   std_logic

  );

end;

architecture rtl of xula_ioport is

signal porta_ddr : std_logic_vector(7 downto 0);

signal portb_ddr : std_logic_vector(7 downto 0);

signal porta_data : std_logic_vector(7 downto 0);

signal portb_data : std_logic_vector(7 downto 0);

begin

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

--

-- read I/O port

--

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

ioport_read : process( addr,

                     porta_ddr, portb_ddr,

                                                        porta_data, portb_data,

                                                   porta_io, portb_io )

variable count : integer;

begin

  case addr is

  when "00" =>

    for count in 0 to 7 loop

      if porta_ddr(count) = '1' then

        data_out(count) <= porta_data(count);

      else

        data_out(count) <= porta_io(count);

      end if;

    end loop;

  when "01" =>

    for count in 0 to 7 loop

      if portb_ddr(count) = '1' then

        data_out(count) <= portb_data(count);

      else

                  if count < 5 then

          data_out(count) <= portb_io(count);

                  else

          data_out(count) <= portc_in(count);

                  end if;

      end if;

    end loop;

  when "10" =>

    data_out <= porta_ddr;

  when "11" =>

    data_out <= portb_ddr;

  when others =>

    null;

  end case;

end process;

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

--

-- Write I/O ports

--

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

ioport_write : process( clk, rst, addr, cs, rw, data_in,

                        porta_data, portb_data,

                                                                porta_ddr, portb_ddr )

begin

  if clk'event and clk = '0' then

    if rst = '1' then

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

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

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

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

    else

      if cs = '1' and rw = '0' then

        case addr is

        when "00" =>

           porta_data <= data_in;

        when "01" =>

           portb_data <= data_in;

        when "10" =>

           porta_ddr  <= data_in;

        when "11" =>

           portb_ddr  <= data_in;

        when others =>

           null;

        end case;

      end if;

    end if;

  end if;

end process;

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

--

-- direction control port a

--

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

porta_direction : process ( porta_data, porta_ddr )

variable count : integer;

begin

  for count in 0 to 7 loop

    if porta_ddr(count) = '1' then

      porta_io(count) <= porta_data(count);

    else

      porta_io(count) <= 'Z';

    end if;

  end loop;

end process;

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

--

-- direction control port b

--

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

portb_direction : process ( portb_data, portb_ddr, portb_io )

variable count : integer;

variable irq_temp : std_logic;

begin

  --

  -- For bit 0 to 4 DDR determines the direction of the port

  --

  for count in 0 to 4 loop

    if portb_ddr(count) = '1' then

      portb_io(count) <= portb_data(count);

    else

      portb_io(count) <= 'Z';

    end if;

  end loop;

  --

  -- For bit 5 to 7 DDR is an interrupt enable

  --

  irq_temp := '0';

  for count in 5 to 7 loop

    irq_temp := (portc_in(count) AND portb_ddr(count)) OR irq_temp;

  end loop;

  irq <= irq_temp;

end process;

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

end rtl;