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[/] [System09/] [trunk/] [rtl/] [System09_Xess_XuLA/] [xula_iobus.vhd] - Rev 134
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--===========================================================================-- -- -- -- xula_iobus.vhd - Synthesizable Dual Bidirectionsal I/O Port -- -- -- --===========================================================================-- -- -- File name : xula_iobusi.vhd -- -- Purpose : Implements a dual 8 bit bidirectional I/O bus -- for the XuLA implementation of System09 -- Allows the XuLA System09 port to talk to -- -- Dependencies : ieee.std_logic_1164 -- ieee.std_logic_unsigned -- unisim.vcomponents -- -- Author : John E. Kent -- -- Email : dilbert57@opencores.org -- -- Web : http://opencores.org/project,system09 -- -- Description -- -- system09 clk /-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\_/-\ -- -- system09 cs ---\_______________________________/-------------------- -- -- bus release ______________________________/------------------------- -- -- system09 hold ____/---------------------------\_______________________ -- -- bus cs_n ----\______________________________/-------------------- -- -- bus rd_n ---------------------\_____________/-------------------- -- -- bus ds _____________________/-------------\____________________ -- -- -- Copyright (C) 2002 - 2011 John Kent -- -- This program is free software: you can redistribute it and/or modify -- it under the terms of the GNU General Public License as published by -- the Free Software Foundation, either version 3 of the License, or -- (at your option) any later version. -- -- This program is distributed in the hope that it will be useful, -- but WITHOUT ANY WARRANTY; without even the implied warranty of -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -- GNU General Public License for more details. -- -- You should have received a copy of the GNU General Public License -- along with this program. If not, see <http://www.gnu.org/licenses/>. -- --===========================================================================-- -- -- -- Revision History -- -- -- --===========================================================================-- -- -- Version Author Date Description -- 0.1 John E. Kent 1 May 2011 Initial version --=========================================================================== -- library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; --library unisim; -- use unisim.vcomponents.all; entity xula_iobus is port ( clk : in std_logic; rst : in std_logic; cs : in std_logic; rw : in std_logic; addr : in std_logic_vector(4 downto 0); data_in : in std_logic_vector(7 downto 0); data_out : out std_logic_vector(7 downto 0); hold : out std_logic; irq : out std_logic; bus_cs : out std_logic; bus_ds_rdn : out std_logic; bus_rw_wrn : out std_logic; bus_addr : out std_logic_vector(3 downto 0); bus_data : inout std_logic_vector(7 downto 0); bus_irq : in std_logic; ); end; architecture rtl of xula_iobus is begin -------------------------------- -- -- read I/O bus control registers -- -------------------------------- iobus_read : process( addr, bus_data, bus_reg ) begin if addr(4) = '0' then data_out <= bus_data; else data_out <= bus_reg; end if; end process; --------------------------------- -- -- Write bus data / register -- --------------------------------- iobus_write : process( clk, rst, addr, cs, rw, data_in ) begin if clk'event and clk = '0' then if rst = '1' then bus_data <= (others=>'Z'); bus_reg <= (others=>'0'); else if cs = '1' then if addr(4) = '0' then if bus_release = '0' and bus_hold = '0' then bus_hold <= '1'; if rw = '0' then bus_data <= data_in; else bus_data <= (other=>'Z'); end if; else if bus_release = '1' and bus_hold = '1' then bus_hold <= '0'; end if; end if; else if rw = '0' then bus_reg <= data_in; end if; end if; end if; end if; end if; end process; --------------------------------- -- -- Write bus register -- --------------------------------- iobus_reg_write : process( clk, rst, addr, cs, rw, data_in ) begin if clk'event and clk = '0' then if rst = '1' then else if cs = '1' and addr(4) = '1' then if rw = '0' then bus_reg <= data_in; else bus_data <= (other=>'Z'); end if; end if; end if; end if; end process; --------------------------------- -- -- direction control port a -- --------------------------------- iobus_ctrl : process ( clk, rst, ) begin if clk'event and clk = '0' then if rst = '1' then bus_data <= (others=>'0'); bus_reg <= (others=>'0'); else end process; --------------------------------- -- -- hold CPU for one external bus cycle -- --------------------------------- iobus_hold : process ( portb_data, portb_ddr, portb_io ) begin end process; --------------------------------- ---------------------------------------------------------- -- -- Generate a bus clock with half cycle period -- equal to the cpu clock cycle count -- in the bus register bits 6 downto 0. -- -- Generate a time out signal for one cpu clock cycle -- when the bus timer reaches zero -- ---------------------------------------------------------- iobus_clk : process ( clk, rst ) begin if clk'event and clk = '0' then if rst = '1' then bus_timer <= (others=>'0'); bus_clk <= '0'; bus_to <= '0'; else if bus_timer = "0000000" then bus_timer <= bus_reg(6 downto 0); bus_clk <= not bus_clk; bus_to <= '1'; else bus_timer <= bus_timer - "0000001"; bus_to <= '0'; end if; end if; end if; end process; ---------------------------------------------------------- -- -- Bus Request -- -- Synchronize I/O bus cycle request to the start of the bus clock -- -- The start of the io bus cycle is defined as there being -- a bus timer timeout and the bus clock is low. -- -- If there is a bus request wait for the start of the -- io bus cycle before acknowledging -- -- If the bus request is removed, wait for the start of the -- io bus cycle before removing the acknowledge. -- ---------------------------------------------------------- iobus_req : process ( clk, rst, bus_req, bus_ack, bus_clk, bus_to ) begin if clk'event and clk = '0' then if rst = '1' then bus_ack <= '0'; else if bus_req = '1' and bus_ack = '0' then if bus_clk = '0' and bus_to = '1' then bus_ack <= '1'; end if; elsif bus_req = '0' and bus_ack = '1' then if bus_clk = '0' and bus_to = '1' then bus_ack <= '0'; end if; end if; end if; end if; end process; end rtl;
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