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[/] [t48/] [tags/] [rel_0_6_beta/] [rtl/] [vhdl/] [db_bus.vhd] - Rev 292
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------------------------------------------------------------------------------- -- -- The BUS unit. -- Implements the BUS port logic. -- -- $Id: db_bus.vhd,v 1.5 2005-06-11 10:08:43 arniml Exp $ -- -- Copyright (c) 2004, Arnim Laeuger (arniml@opencores.org) -- -- All rights reserved -- -- Redistribution and use in source and synthezised 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 synthesized 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. -- -- Neither the name of the author nor the names of other contributors may -- be used to endorse or promote products derived from this software without -- specific prior written permission. -- -- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 THE AUTHOR OR CONTRIBUTORS 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 (INCLUDING NEGLIGENCE OR OTHERWISE) -- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE -- POSSIBILITY OF SUCH DAMAGE. -- -- Please report bugs to the author, but before you do so, please -- make sure that this is not a derivative work and that -- you have the latest version of this file. -- -- The latest version of this file can be found at: -- http://www.opencores.org/cvsweb.shtml/t48/ -- ------------------------------------------------------------------------------- library ieee; use ieee.std_logic_1164.all; use work.t48_pack.word_t; entity t48_db_bus is port ( -- Global Interface ------------------------------------------------------- clk_i : in std_logic; res_i : in std_logic; en_clk_i : in boolean; ea_i : in std_logic; -- T48 Bus Interface ------------------------------------------------------ data_i : in word_t; data_o : out word_t; write_bus_i : in boolean; read_bus_i : in boolean; -- BUS Interface ---------------------------------------------------------- output_pcl_i : in boolean; bidir_bus_i : in boolean; pcl_i : in word_t; db_i : in word_t; db_o : out word_t; db_dir_o : out std_logic ); end t48_db_bus; use work.t48_pack.clk_active_c; use work.t48_pack.res_active_c; use work.t48_pack.bus_idle_level_c; use work.t48_pack.to_stdLogic; architecture rtl of t48_db_bus is -- the BUS output register signal bus_q : word_t; -- BUS direction marker signal db_dir_q, db_dir_qq : std_logic; begin ----------------------------------------------------------------------------- -- Process bus_regs -- -- Purpose: -- Implements the BUS output register. -- bus_regs: process (res_i, clk_i) begin if res_i = res_active_c then bus_q <= (others => '0'); db_dir_q <= '0'; db_dir_qq <= '0'; elsif clk_i'event and clk_i = clk_active_c then if en_clk_i then if write_bus_i then db_dir_qq <= '1'; else -- extend bus direction by one machine cycle db_dir_qq <= db_dir_q; end if; if write_bus_i then bus_q <= data_i; db_dir_q <= '1'; elsif ea_i = '1' or bidir_bus_i then db_dir_q <= '0'; end if; end if; end if; end process bus_regs; -- ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- -- Output Mapping. ----------------------------------------------------------------------------- db_o <= pcl_i when output_pcl_i else bus_q; db_dir_o <= db_dir_qq or to_stdLogic(output_pcl_i); data_o <= (others => bus_idle_level_c) when not read_bus_i else db_i; end rtl; ------------------------------------------------------------------------------- -- File History: -- -- $Log: not supported by cvs2svn $ -- Revision 1.4 2005/06/09 22:16:26 arniml -- Implement db_dir_o glitch-safe -- -- Revision 1.3 2004/10/25 20:30:18 arniml -- delay db_dir_o by one machine cycle -- this fixes the timing relation between BUS data and WR' -- -- Revision 1.2 2004/04/04 14:15:45 arniml -- add dump_compare support -- -- Revision 1.1 2004/03/23 21:31:52 arniml -- initial check-in -- -------------------------------------------------------------------------------