Subversion Repositories open8_urisc

-- Copyright (c)2006, 2016, 2019, 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

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-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

--

-- VHDL Units :  o8_datalatch

-- Description:  Latches a byte of external data and issues an interrupt on

--                capture.

--

--

-- Register Map:

-- Offset  Bitfield Description                        Read/Write

--   0x00  AAAAAAAA Latched Value                      (RW)

--

-- Note: Cut the path between LData_q1 and L_Data for timing analysis

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      01/22/20 Design Start

-- Seth Henry      04/16/20 Modified to use Open8 bus record

library ieee;

use ieee.std_logic_1164.all;

library work;

  use work.open8_pkg.all;

entity o8_datalatch is

generic(

  Address                    : ADDRESS_TYPE

);

port(

  Open8_Bus                  : in  OPEN8_BUS_TYPE;

  Rd_Data                    : out DATA_TYPE;

  Interrupt                  : out std_logic;

  --

  L_Strobe                   : in  std_logic;

  L_Data                     : in  DATA_TYPE

);

end entity;

architecture behave of o8_datalatch is

  alias Clock                is Open8_Bus.Clock;

  alias Reset                is Open8_Bus.Reset;

  constant User_Addr         : std_logic_vector(15 downto 0) := Address;

  alias  Comp_Addr           is Open8_Bus.Address(15 downto 0);

  signal Addr_Match          : std_logic := '0';

  signal Rd_En_d             : std_logic := '0';

  signal Rd_En_q             : std_logic := '0';

  signal Strobe_sr           : std_logic_vector(3 downto 0) := "0000";

  signal Strobe_re           : std_logic := '0';

  signal LData_q1            : DATA_TYPE := x"00";

  signal LData_q2            : DATA_TYPE := x"00";

  signal LData_q3            : DATA_TYPE := x"00";

begin

  Addr_Match                 <= Open8_Bus.Rd_En when Comp_Addr = User_Addr else '0';

  Strobe_re                  <= Strobe_sr(2) and not Strobe_sr(3);

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Rd_En_q                <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

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

      Interrupt              <= '0';

      LData_q1               <= x"00";

      LData_q2               <= x"00";

      LData_q3               <= x"00";

    elsif( rising_edge( Clock ) )then

      Strobe_sr              <= Strobe_sr(2 downto 0) & L_Strobe;

      LData_q1               <= L_Data;

      LData_q2               <= LData_q1;

      Interrupt              <= Strobe_re;

      if( Strobe_re = '1' )then

        LData_q3             <= LData_q2;

      end if;

      Rd_Data                <= OPEN8_NULLBUS;

      Rd_En_q                <= Rd_En_d;

      if( Rd_En_q = '1' )then

        Rd_Data              <= LData_q3;

      end if;

    end if;

  end process;

end architecture;