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

--                                                                           --

--  keyboard.vhd - Synthesizable Interface to PS/2 Keyboard Module           --

--                                                                           --

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

--

--  File name      : keyboard.vhd

--

--  Entity name    : keyboard

--

--  Purpose        : Implements a CPU interface to John Clayton's PS/2 Keyboard

--                  

--  Dependencies   : ieee.std_logic_1164

--                   ieee.std_logic_arith

--                   ieee.std_logic_unsigned

--                   ieee.numeric_std

--                   unisim.vcomponents

--

--  Uses           : ps2_keyboard_interface

--

--  Author         : John E. Kent

--

--  Email          : dilbert57@opencores.org      

--

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

--

--  Registers      :

--

--  IO address + 0 read - Status Register

--

--      Bit[0] - RX Data Ready

--      Bit[1] - TX Data Empty

--      Bit[2] - Extended

--      Bit[3] - Released

--      Bit[4] - Shift On

--      Bit[5] - Error (no keyboard acknowledge received)

--      Bit[6] - TX Interrupt Flag

--      Bit[7] - RX Interrupt Flag

--

--  IO address + 0 write - Control Register

--

--      Bit[0] - Undefined

--      Bit[1] - Undefined

--      Bit[2] - Undefined

--      Bit[3] - Undefined

--      Bit[4] - Undefined

--      Bit[5] - Undefined

--      Bit[6] - TX Interrupt Enable

--      Bit[7] - RX Interrupt Enable

--

--  IO address + 1 read - Receive Data Register

--

--  IO address + 1 write - Transmit Data Register

--

--  Copyright (C) 2004 - 2010 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 Kent  2nd April 2004     Interface to John Clayton's PS2 keyboard

-- 0.2      John Kent  7th Februaury 2007 Added Generics for Keyboard Timing

-- 0.3      John Kent  30th May 2010      Updated Header, added unisim library

-- 0.4      John Kent  17th June 2010     Cleaned up signal names, 

--                                        added TX interrupt enable

--                                        Modified assignment of status register

--                                        Revised hanshake control and input registers

--                                        

library ieee;

   use ieee.std_logic_1164.all;

   use ieee.std_logic_arith.all;

   use ieee.std_logic_unsigned.all;

   use ieee.numeric_std.all;

library unisim;

   use unisim.vcomponents.all;

entity keyboard is

  generic (

  KBD_CLK_FREQ : integer

  );

  port(

  --

  -- CPU Interface Signals

  --

  clk             : in    std_logic;

  rst             : in    std_logic;

  cs              : in    std_logic;

  addr            : in    std_logic;

  rw              : in    std_logic;

  data_in         : in    std_logic_vector(7 downto 0);

  data_out        : out   std_logic_vector(7 downto 0);

  irq             : out   std_logic;

  --

  -- Keyboard Interface Signals

  --

  kbd_clk         : inout std_logic;

  kbd_data        : inout std_logic

  );

end keyboard;

architecture rtl of keyboard is

constant CLK_FREQ_MHZ : integer := KBD_CLK_FREQ / 1000000;

signal kbd_status     : std_logic_vector(7 downto 0);

signal kbd_control    : std_logic_vector(7 downto 0);

signal kbd_rx_data    : std_logic_vector(7 downto 0);

signal kbd_tx_data    : std_logic_vector(7 downto 0);

signal kbd_read       : std_logic;

signal kbd_write      : std_logic;

signal kbd_data_ready : std_logic; --  => kbd_status(0)

signal kbd_data_empty : std_logic; --  => kbd_status(1)

signal kbd_extended   : std_logic; --  => kbd_status(2)

signal kbd_released   : std_logic; --  => kbd_status(3)

signal kbd_shift_on   : std_logic; --  => kbd_status(4)

signal kbd_error      : std_logic; --  => kbd_status(5) (No receive acknowledge)

component ps2_keyboard

  generic (

  CLK_FREQ_MHZ    : integer := CLK_FREQ_MHZ

  );

  port(

  clk             : in    std_logic;

  reset           : in    std_logic;

  rx_data         : out   std_logic_vector(7 downto 0);

  rx_read         : in    std_logic;

  rx_data_ready   : out   std_logic;

  rx_extended     : out   std_logic;

  rx_released     : out   std_logic;

  rx_shift_on     : out   std_logic;

  tx_data         : in    std_logic_vector(7 downto 0);

  tx_write        : in    std_logic;

  tx_data_empty   : out   std_logic;

  tx_error        : out   std_logic;

  ps2_clk         : inout std_logic;

  ps2_data        : inout std_logic

  );

end component;

begin

my_ps2_keyboard : ps2_keyboard

  generic map (

  CLK_FREQ_MHZ   => CLK_FREQ_MHz

  )

  port map(

  clk             => clk,

  reset           => rst,

  rx_data         => kbd_rx_data,

  rx_read         => kbd_read,

  rx_data_ready   => kbd_data_ready,

  rx_extended     => kbd_extended,

  rx_released     => kbd_released,

  rx_shift_on     => kbd_shift_on,

  tx_data         => kbd_tx_data,

  tx_write        => kbd_write,

  tx_data_empty   => kbd_data_empty,

  tx_error        => kbd_error,

  ps2_clk         => kbd_clk,

  ps2_data        => kbd_data

  );

  --

  -- Keyboard Read strobe

  --

  keyboard_read : process( clk, rst, cs, rw, kbd_data_ready  )

  begin

    if rst = '1' then

      kbd_read <= '0';

    elsif( clk'event and clk='0' ) then

      if( cs = '1' and addr = '1' and rw = '1' ) then

        kbd_read <= '1';

      elsif kbd_data_ready = '1' then

        kbd_read <= '0';

      end if;

    end if;

  end process;

  --

  -- Keyboard Write strobe

  --

  keyboard_write : process( clk, rst, cs, rw, addr,

                                                                         kbd_write, kbd_data_empty )

  begin

    if rst = '1' then

                kbd_write   <= '0';

    elsif( clk'event and clk='0' ) then

                if( cs = '1' and addr = '1' and rw = '0' ) then

         kbd_write <= '1';

      elsif kbd_data_empty = '1' then

         kbd_write <= '0';

      end if;

    end if;

  end process;

  --

  -- Keyboard register input

  --

  keyboard_in : process( clk, rst, cs, rw, addr, data_in, kbd_rx_data )

  begin

    if rst = '1' then

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

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

    elsif( clk'event and clk='0' ) then

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

         if addr = '0' then

            kbd_control <= data_in;

         else

            kbd_tx_data <= data_in;

         end if;

      end if;

    end if;

  end process;

  --

  -- Keyboard register output

  --

  keyboard_out : process( addr, kbd_rx_data, kbd_status )

  begin

    if( addr = '0' ) then

      data_out <= kbd_status;

    else

      data_out <= kbd_rx_data;

    end if;

  end process;

  --

  -- Assign Keyboard Status bits

  --

  keyboard_status : process( kbd_data_ready, kbd_data_empty,

                             kbd_extended, kbd_released, kbd_shift_on, kbd_error,

                             kbd_control)

  begin

    kbd_status(0) <= kbd_data_ready;

    kbd_status(1) <= kbd_data_empty;

    kbd_status(2) <= kbd_extended;

    kbd_status(3) <= kbd_released;

    kbd_status(4) <= kbd_shift_on;

    kbd_status(5) <= kbd_error;

    kbd_status(6) <= kbd_control(6) and kbd_data_empty; -- TX Interrupt Flag

    kbd_status(7) <= kbd_control(7) and kbd_data_ready; -- RX Interrupt Flag

    irq           <= kbd_status(7) or kbd_status(6);

  end process;

end rtl;