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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_gpin.vhd] - Blame information for rev 213

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-- Copyright (c)2011, 2019 Jeremy Seth Henry
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-- All rights reserved.
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--
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-- Redistribution and use in source and binary forms, with or without
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-- modification, are permitted provided that the following conditions are met:
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--     * Redistributions of source code must retain the above copyright
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--       notice, this list of conditions and the following disclaimer.
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--     * Redistributions in binary form must reproduce the above copyright
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--       notice, this list of conditions and the following disclaimer in the
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--       documentation and/or other materials provided with the distribution,
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--       where applicable (as part of a user interface, debugging port, etc.)
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--
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-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``AS IS'' AND ANY
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-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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-- DISCLAIMED. IN NO EVENT SHALL JEREMY SETH HENRY BE LIABLE FOR ANY
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-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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--
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-- VHDL Units :  o8_gpin
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-- Description:  Provides a single 8-bit input register
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--
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-- Note: Cut the path between GPIN and GPIN_q1 for timing analysis
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--
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-- Revision History
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-- Author          Date     Change
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------------------ -------- ---------------------------------------------------
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-- Seth Henry      07/28/11 Design Start
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-- Seth Henry      12/19/19 Renamed to "o8_gpin" to fit "theme"
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-- Seth Henry      12/20/19 Added metastability registers
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-- Seth Henry      04/10/20 Code Cleanup
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library ieee;
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use ieee.std_logic_1164.all;
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library work;
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  use work.open8_pkg.all;
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entity o8_gpin is
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generic(
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  Reset_Level                : std_logic;
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  Address                    : ADDRESS_TYPE
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);
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port(
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  Clock                      : in  std_logic;
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  Reset                      : in  std_logic;
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  --
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  Bus_Address                : in  ADDRESS_TYPE;
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  Rd_Enable                  : in  std_logic;
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  Rd_Data                    : out DATA_TYPE;
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  --
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  GPIN                       : in  DATA_TYPE
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);
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end entity;
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architecture behave of o8_gpin is
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  constant User_Addr         : std_logic_vector(15 downto 0) := Address;
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  alias  Comp_Addr           is Bus_Address(15 downto 0);
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  signal Addr_Match          : std_logic;
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  signal Rd_En               : std_logic;
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  signal GPIN_q1             : DATA_TYPE;
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  signal GPIN_q2             : DATA_TYPE;
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  signal User_In             : DATA_TYPE;
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begin
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  Addr_Match                 <= Rd_Enable when Comp_Addr = User_Addr else '0';
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  io_reg: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      Rd_En                  <= '0';
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      Rd_Data                <= OPEN8_NULLBUS;
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      GPIN_q1                <= x"00";
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      GPIN_q2                <= x"00";
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      User_In                <= x"00";
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    elsif( rising_edge( Clock ) )then
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      GPIN_q1                <= GPIN;
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      GPIN_q2                <= GPIN_q1;
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      User_In                <= GPIN_q2;
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      Rd_Data                <= OPEN8_NULLBUS;
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      Rd_En                  <= Addr_Match;
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      if( Rd_En = '1' )then
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        Rd_Data              <= User_In;
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      end if;
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    end if;
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  end process;
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end architecture;

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