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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_register.vhd] - Blame information for rev 215

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Line No. Rev Author Line
1 194 jshamlet
-- Copyright (c)2006, 2016, 2019, 2020 Jeremy Seth Henry
2 180 jshamlet
-- 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
21 194 jshamlet
-- (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_register
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-- Description:  Provides a single addressible 8-bit output register
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--
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-- Register Map:
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-- Offset  Bitfield Description                        Read/Write
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--   0x00  AAAAAAAA Registered Outputs                    (RW)
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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      12/20/19 Design Start
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library ieee;
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  use ieee.std_logic_1164.all;
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  use ieee.std_logic_unsigned.all;
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  use ieee.std_logic_arith.all;
40 191 jshamlet
  use ieee.std_logic_misc.all;
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library work;
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  use work.open8_pkg.all;
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entity o8_register is
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generic(
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  Default_Value         : DATA_TYPE := x"00";
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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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  Wr_Enable             : in  std_logic;
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  Wr_Data               : in  DATA_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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  Register_Out          : out DATA_TYPE
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);
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end entity;
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architecture behave of o8_register is
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  function ceil_log2 (x : in natural) return natural is
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    variable retval     : natural;
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  begin
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    retval              := 1;
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    while ((2**retval) - 1) < x loop
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      retval            := retval + 1;
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    end loop;
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    return retval;
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  end function;
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  constant User_Addr    : std_logic_vector(15 downto 0)
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                          := Address(15 downto 0);
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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 Wr_En          : std_logic;
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  signal Wr_Data_q      : DATA_TYPE;
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  signal Reg_Out        : DATA_TYPE;
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  signal Rd_En          : std_logic;
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begin
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  Addr_Match            <= '1' 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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      Wr_En             <= '0';
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      Wr_Data_q         <= (others => '0');
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      Reg_Out           <= Default_Value;
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      Rd_En             <= '0';
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      Rd_Data           <= OPEN8_NULLBUS;
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    elsif( rising_edge( Clock ) )then
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      Wr_En             <= Addr_Match and Wr_Enable;
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      Wr_Data_q         <= Wr_Data;
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      if( Wr_En = '1' )then
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        Reg_Out         <= Wr_Data_q;
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      end if;
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      Rd_Data           <= OPEN8_NULLBUS;
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      Rd_En             <= Addr_Match and Rd_Enable;
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      if( Rd_En = '1' )then
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        Rd_Data         <= Reg_Out;
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      end if;
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    end if;
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  end process;
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  Register_Out          <= Reg_Out;
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end architecture;

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