Subversion Repositories open8_urisc

-- Copyright (c)2013, 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
-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--
-- VHDL Units :  o8_gpout
-- Description:  Provides a single 8-bit GP output register with selectable
--            :   tri-state control.
-- Notes      :  Requires 1 bit from the address bus (two locations).
--            :  Sequential instantiations should be separated by 2.
 
library ieee;
use ieee.std_logic_1164.all;
 
library work;
  use work.open8_pkg.all;
 
entity o8_gpout is
generic(
  Default_Out           : DATA_TYPE := x"00";
  Default_En            : DATA_TYPE := x"00";
  Disable_Tristate      : boolean   := false;
  Reset_Level           : std_logic;
  Address               : ADDRESS_TYPE
);
port(
  Clock                 : in  std_logic;
  Reset                 : in  std_logic;
  --
  Bus_Address           : in  ADDRESS_TYPE;
  Wr_Enable             : in  std_logic;
  Wr_Data               : in  DATA_TYPE;
  Rd_Enable             : in  std_logic;
  Rd_Data               : out DATA_TYPE;
  --
  GPO                   : out DATA_TYPE
);
end entity;
 
architecture behave of o8_gpout is
 
  constant User_Addr    : std_logic_vector(15 downto 1)
                          := Address(15 downto 1);
  alias  Comp_Addr      is Bus_Address(15 downto 1);
  alias  Reg_Addr       is Bus_Address(0);
  signal Reg_Sel        : std_logic;
  signal Addr_Match     : std_logic;
  signal Wr_En          : std_logic;
  signal Wr_Data_q      : DATA_TYPE;
  signal Rd_En          : std_logic;
 
  signal User_Out       : DATA_TYPE;
  signal User_En        : DATA_TYPE;
 
begin
 
  Addr_Match            <= '1' when Comp_Addr = User_Addr else '0';
 
  io_reg: process( Clock, Reset )
  begin
    if( Reset = Reset_Level )then
      Reg_Sel           <= '0';
      Wr_En             <= '0';
      Wr_Data_q         <= x"00";
      Rd_En             <= '0';
      Rd_Data           <= OPEN8_NULLBUS;
      User_Out          <= Default_Out;
      if( not Disable_Tristate)then
        User_En         <= Default_En;
      end if;
    elsif( rising_edge( Clock ) )then
      Reg_Sel           <= Reg_Addr;
      Wr_En             <= Addr_Match and Wr_Enable;
      Wr_Data_q         <= Wr_Data;
      if( Wr_En = '1' )then
        if( Disable_Tristate )then
          User_Out      <= Wr_Data_q;
        else
          if( Reg_Sel = '0' )then
            User_Out    <= Wr_Data_q;
          else
            User_En     <= Wr_Data_q;
          end if;
        end if;
      end if;
 
      Rd_Data           <= OPEN8_NULLBUS;
      Rd_En             <= Addr_Match and Rd_Enable;
      if( Rd_En = '1' )then
        Rd_Data         <= User_Out;
        if( (Reg_Sel = '1') and (not Disable_Tristate) )then
          Rd_Data       <= User_En;
        end if;
      end if;
    end if;
  end process;
 
No_Tristates: if( Disable_Tristate )generate
  GPO                   <= User_Out;
end generate;
 
Tristates: if( not Disable_Tristate )generate
 
  Output_Ctl_proc: process( User_Out, User_En )
  begin
    for i in 0 to 7 loop
      GPO(i)            <= 'Z';
      if( User_En(i) = '1' )then
        GPO(i)          <= User_Out(i);
      end if;
    end loop;
  end process;
 
end generate;
 
end architecture;