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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_ram_1k.vhd] - Blame information for rev 298

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-- Copyright (c)2013, 2020 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_ram_1k
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-- Description:  Provides a wrapper layer for a 1kx8 RAM model with interface
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--            :   logic for the Open8 CPU. Also provides an optional write
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--            :   enable register that prevents regions from being written
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--            :   by non-ISR code (uses the I flag) as a way to prevent tasks
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--            :   from inadvertently writing outside of their designated
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--            :   memory space.
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--            :  When enabled, the write mask logically divides the memory into
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--            :   16, 64 byte regions, corresponding to the 16 bits in the WPR
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--            :   register.
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--
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-- WP Register Map:
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-- Offset  Bitfield Description                        Read/Write
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--   0x00  AAAAAAAA Region Enables  7:0                  (RW)
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--   0x01  AAAAAAAA Region Enables 15:8                  (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      04/16/20 Revision block added
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-- Seth Henry      05/12/20 Added write protect logic
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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;
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library work;
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  use work.open8_pkg.all;
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entity o8_ram_1k is
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generic(
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  Write_Protect              : boolean := FALSE;
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  Default_Mask               : ADDRESS_TYPE := x"0000";
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  Address_WPR                : ADDRESS_TYPE := x"0400";
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  Address_RAM                : ADDRESS_TYPE
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);
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port(
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  Open8_Bus                  : in  OPEN8_BUS_TYPE;
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  Rd_Data                    : out DATA_TYPE;
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  Write_Fault                : out std_logic
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);
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end entity;
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architecture behave of o8_ram_1k is
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  alias  Clock               is Open8_Bus.Clock;
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  alias  Reset               is Open8_Bus.Reset;
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  alias  ISR_En              is Open8_Bus.GP_Flags(EXT_ISR);
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  alias  Wr_En               is Open8_Bus.Wr_En;
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  alias  Rd_En               is Open8_Bus.Rd_En;
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  constant WPR_User_Addr     : std_logic_vector(15 downto 1)
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                               := Address_WPR(15 downto 1);
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  constant RAM_User_Addr     : std_logic_vector(15 downto 10)
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                               := Address_RAM(15 downto 10);
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  alias  WPR_Comp_Addr       is Open8_Bus.Address(15 downto 1);
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  signal WPR_Addr_Match      : std_logic := '0';
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  alias  WPR_Reg_Sel_d       is Open8_Bus.Address(0);
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  signal WPR_Reg_Sel_q       : std_logic := '0';
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  alias  Wr_Data_d           is Open8_Bus.Wr_Data;
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  signal WPR_Wr_Data_q       : DATA_TYPE := x"00";
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  signal Write_Mask          : std_logic_vector(15 downto 0) :=
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                                x"0000";
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  alias  Write_Mask_0        is Write_Mask(7 downto 0);
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  alias  Write_Mask_1        is Write_Mask(15 downto 8);
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  signal WPR_Wr_En_d         : std_logic := '0';
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  signal WPR_Wr_En_q         : std_logic := '0';
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  signal WPR_Rd_En_d         : std_logic := '0';
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  signal WPR_Rd_En_q         : std_logic := '0';
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  alias  RAM_Base_Addr       is Open8_Bus.Address(15 downto 10);
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  alias  RAM_Addr            is Open8_Bus.Address(9 downto 0);
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  alias  RAM_Rgn_Addr        is Open8_Bus.Address(9 downto 6);
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  signal RAM_Region_Match    : std_logic := '0';
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  signal RAM_Addr_Match      : std_logic := '0';
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  signal RAM_Wr_En_d         : std_logic := '0';
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  signal RAM_Rd_En_d         : std_logic := '0';
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  signal RAM_Rd_En_q         : std_logic := '0';
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  signal RAM_Rd_Data         : DATA_TYPE := OPEN8_NULLBUS;
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  signal Write_Fault_d       : std_logic := '0';
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begin
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Write_Protect_On : if( Write_Protect )generate
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  WPR_Addr_Match             <= '1' when WPR_Comp_Addr = WPR_User_Addr else '0';
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  WPR_Wr_En_d                <= WPR_Addr_Match and Wr_En and ISR_En;
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  WPR_Rd_En_d                <= WPR_Addr_Match and Rd_En;
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  RAM_Addr_Match             <= '1' when RAM_Base_Addr = RAM_User_Addr else '0';
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  RAM_Region_Match           <= Write_Mask(conv_integer(RAM_Rgn_Addr)) or
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                                ISR_En;
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  RAM_Rd_En_d                <= RAM_Addr_Match and Rd_En;
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  RAM_Wr_En_d                <= RAM_Addr_Match and RAM_Region_Match and Wr_En;
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  Write_Fault_d              <= RAM_Addr_Match and (not RAM_Region_Match) and Wr_En;
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  RAM_proc: process( Reset, Clock )
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  begin
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    if( Reset = Reset_Level )then
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      WPR_Reg_Sel_q          <= '0';
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      WPR_Wr_Data_q          <= x"00";
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      WPR_Wr_En_q            <= '0';
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      WPR_Rd_En_q            <= '0';
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      Write_Mask             <= Default_Mask;
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      RAM_Rd_En_q            <= '0';
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      Rd_Data                <= OPEN8_NULLBUS;
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      Write_Fault            <= '0';
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    elsif( rising_edge(Clock) )then
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      WPR_Reg_Sel_q          <= WPR_Reg_Sel_d;
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      WPR_Wr_En_q            <= WPR_Wr_En_d;
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      WPR_Wr_Data_q          <= Wr_Data_d;
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      if( WPR_Wr_En_q = '1' )then
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        case( WPR_Reg_Sel_q )is
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          when '0' =>
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            Write_Mask_0     <= WPR_Wr_Data_q;
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          when '1' =>
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            Write_Mask_1     <= WPR_Wr_Data_q;
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          when others =>
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            null;
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        end case;
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      end if;
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      WPR_Rd_En_q            <= WPR_Rd_En_d;
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      RAM_Rd_En_q            <= RAM_Rd_En_d;
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      Rd_Data                <= OPEN8_NULLBUS;
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      if( RAM_Rd_En_q = '1' )then
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        Rd_Data              <= RAM_Rd_Data;
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      elsif( WPR_Rd_En_q = '1'  )then
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        case( WPR_Reg_Sel_q )is
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          when '0' =>
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            Rd_Data          <= Write_Mask_0;
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          when '1' =>
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            Rd_Data          <= Write_Mask_1;
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          when others =>
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            null;
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        end case;
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      end if;
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      Write_Fault            <= Write_Fault_d;
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    end if;
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  end process;
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end generate;
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Write_Protect_Off : if( not Write_Protect )generate
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  Write_Fault                <= '0';
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  RAM_Addr_Match             <= '1' when RAM_Base_Addr = RAM_User_Addr else '0';
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  RAM_Rd_En_d                <= RAM_Addr_Match and Open8_Bus.Rd_En;
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  RAM_Wr_En_d                <= RAM_Addr_Match and Open8_Bus.Wr_En;
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  RAM_proc: process( Reset, Clock )
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  begin
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    if( Reset = Reset_Level )then
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      RAM_Rd_En_q            <= '0';
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      Rd_Data                <= OPEN8_NULLBUS;
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    elsif( rising_edge(Clock) )then
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      RAM_Rd_En_q            <= RAM_Rd_En_d;
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      Rd_Data                <= OPEN8_NULLBUS;
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      if( RAM_Rd_En_q = '1' )then
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        Rd_Data              <= RAM_Rd_Data;
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      end if;
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    end if;
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  end process;
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end generate;
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  -- Note that this RAM should be created without an output FF (unregistered Q)
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  U_RAM : entity work.ram_1k_core
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  port map(
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    address                  => RAM_Addr,
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    clock                    => Clock,
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    data                     => Wr_Data_d,
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    wren                     => RAM_Wr_En_d,
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    q                        => RAM_Rd_Data
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  );
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end architecture;

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