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-- $Id: pia_timer.vhd,v 1.2 2008-03-14 15:52:46 dilbert57 Exp $
--===========================================================================--
--
--  S Y N T H E Z I A B L E    I/O Port   C O R E
--
--  www.OpenCores.Org - May 2004
--  This core adheres to the GNU public license  
--
-- File name      : pia_timer.vhd
--
-- Purpose        : Implements 2 x 8 bit parallel I/O ports
--                  with 8 bit presetable counter.
--                  port a = output connected to presettable counter input
--                  port b = input connected to counter output
--                  
-- Dependencies   : ieee.Std_Logic_1164
--                  ieee.std_logic_unsigned
--
-- Author         : John E. Kent      
--
--===========================================================================----
--
-- Revision History:
--
-- Date:          Revision         Author
-- 1 May 2004     0.0              John Kent
-- Initial version developed from ioport.vhd
--
-- 22 April 2006  1.0              John Kent
-- Removed I/O ports and hard wired a binary
-- down counter. Port A is the preset output.
-- Port B is the timer count input.
-- CA1 & CB1 are interrupt inputs
-- CA2 is the counter load (active low)
-- CB2 is the counter reset (active high)
-- It may be necessary to offset the counter
-- to compensate for differences in cpu cycle
-- times between FPGA and real 6809 systems.
--
-- 24 May 2006	1.1					John Kent
-- Modified counter to subtract one from preset
-- so FPGA version of the CMC_BUG monitor is
-- compatible with the reference design.
--
--===========================================================================----
--
-- Memory Map
--
-- IO + $00 - Port A Data & Direction register
-- IO + $01 - Port A Control register
-- IO + $02 - Port B Data & Direction Direction Register
-- IO + $03 - Port B Control Register
--
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
 
entity pia_timer is
	port (	
	 clk       : in    std_logic;
    rst       : in    std_logic;
    cs        : in    std_logic;
    rw        : in    std_logic;
    addr      : in    std_logic_vector(1 downto 0);
    data_in   : in    std_logic_vector(7 downto 0);
	 data_out  : out   std_logic_vector(7 downto 0);
	 irqa      : out   std_logic;
	 irqb      : out   std_logic
	 );
end;
 
architecture pia_arch of pia_timer is
 
signal pa          : std_logic_vector(7 downto 0);
signal porta_ddr   : std_logic_vector(7 downto 0);
signal porta_data  : std_logic_vector(7 downto 0);
signal porta_ctrl  : std_logic_vector(5 downto 0);
signal porta_read  : std_logic;
 
signal pb          : std_logic_vector(7 downto 0);
signal portb_ddr   : std_logic_vector(7 downto 0);
signal portb_data  : std_logic_vector(7 downto 0);
signal portb_ctrl  : std_logic_vector(5 downto 0);
signal portb_read  : std_logic;
signal portb_write : std_logic;
 
signal ca1         : std_logic;
signal ca1_del     : std_logic;
signal ca1_rise    : std_logic;
signal ca1_fall    : std_logic;
signal ca1_edge    : std_logic;
signal irqa1       : std_logic;
 
signal ca2         : std_logic;
signal ca2_del     : std_logic;
signal ca2_rise    : std_logic;
signal ca2_fall    : std_logic;
signal ca2_edge    : std_logic;
signal irqa2       : std_logic;
signal ca2_out     : std_logic;
 
signal cb1         : std_logic;
signal cb1_del     : std_logic;
signal cb1_rise    : std_logic;
signal cb1_fall    : std_logic;
signal cb1_edge    : std_logic;
signal irqb1       : std_logic;
 
signal cb2         : std_logic;
signal cb2_del     : std_logic;
signal cb2_rise    : std_logic;
signal cb2_fall    : std_logic;
signal cb2_edge    : std_logic;
signal irqb2       : std_logic;
signal cb2_out     : std_logic;
 
-- 74193 down counter
signal timer       : std_logic_vector(7 downto 0);
 
begin
 
--------------------------------
--
-- read I/O port
--
--------------------------------
 
pia_read : process(  addr,	cs,
                     irqa1, irqa2, irqb1, irqb2,
                     porta_ddr,  portb_ddr,
							porta_data, portb_data,
							porta_ctrl, portb_ctrl,
						   pa,         pb )
variable count : integer;
begin
      case addr is
	     when "00" =>
		    for count in 0 to 7 loop
			   if porta_ctrl(2) = '0' then
				  data_out(count) <= porta_ddr(count);
			     porta_read <= '0';
            else
				  if porta_ddr(count) = '1' then
                data_out(count) <= porta_data(count);
              else
                data_out(count) <= pa(count);
              end if;
			     porta_read <= cs;
            end if;
			 end loop;
			 portb_read <= '0';
 
	     when "01" =>
		    data_out <= irqa1 & irqa2 & porta_ctrl;
			 porta_read <= '0';
			 portb_read <= '0';
 
		  when "10" =>
		    for count in 0 to 7 loop
			   if portb_ctrl(2) = '0' then
				  data_out(count) <= portb_ddr(count);
				  portb_read <= '0';
            else
				  if portb_ddr(count) = '1' then
                data_out(count) <= portb_data(count);
              else
                data_out(count) <= pb(count);
				  end if;
				  portb_read <= cs;
            end if;
			 end loop;
			 porta_read <= '0';
 
		  when "11" =>
		    data_out <= irqb1 & irqb2 & portb_ctrl;
			 porta_read <= '0';
			 portb_read <= '0';
 
		  when others =>
		    data_out <= "00000000";
			 porta_read <= '0';
			 portb_read <= '0';
 
		end case;
end process;
 
---------------------------------
--
-- Write I/O ports
--
---------------------------------
 
pia_write : process( clk, rst, addr, cs, rw, data_in,
                        porta_ctrl, portb_ctrl,
                        porta_data, portb_data,
								porta_ctrl, portb_ctrl,
								porta_ddr, portb_ddr )
begin
  if rst = '1' then
      porta_ddr   <= "00000000";
      porta_data  <= "00000000";
      porta_ctrl  <= "000000";
      portb_ddr   <= "00000000";
      portb_data  <= "00000000";
		portb_ctrl  <= "000000";
		portb_write <= '0';
  elsif clk'event and clk = '1' then
    if cs = '1' and rw = '0' then
      case addr is
	     when "00" =>
		    if porta_ctrl(2) = '0' then
		       porta_ddr  <= data_in;
		       porta_data <= porta_data;
			 else
		       porta_ddr  <= porta_ddr;
		       porta_data <= data_in;
			 end if;
			 porta_ctrl  <= porta_ctrl;
		    portb_ddr   <= portb_ddr;
		    portb_data  <= portb_data;
			 portb_ctrl  <= portb_ctrl;
			 portb_write <= '0';
		  when "01" =>
		    porta_ddr   <= porta_ddr;
		    porta_data  <= porta_data;
			 porta_ctrl  <= data_in(5 downto 0);
		    portb_ddr   <= portb_ddr;
		    portb_data  <= portb_data;
			 portb_ctrl  <= portb_ctrl;
			 portb_write <= '0';
	     when "10" =>
		    porta_ddr   <= porta_ddr;
		    porta_data  <= porta_data;
			 porta_ctrl  <= porta_ctrl;
		    if portb_ctrl(2) = '0' then
		       portb_ddr   <= data_in;
		       portb_data  <= portb_data;
			    portb_write <= '0';
			 else
		       portb_ddr   <= portb_ddr;
		       portb_data  <= data_in;
			    portb_write <= '1';
			 end if;
			 portb_ctrl  <= portb_ctrl;
		  when "11" =>
		    porta_ddr   <= porta_ddr;
		    porta_data  <= porta_data;
			 porta_ctrl  <= porta_ctrl;
		    portb_ddr   <= portb_ddr;
		    portb_data  <= portb_data;
			 portb_ctrl  <= data_in(5 downto 0);
			 portb_write <= '0';
		  when others =>
		    porta_ddr   <= porta_ddr;
		    porta_data  <= porta_data;
			 porta_ctrl  <= porta_ctrl;
		    portb_ddr   <= portb_ddr;
		    portb_data  <= portb_data;
			 portb_ctrl  <= portb_ctrl;
			 portb_write <= '0';
		end case;
	 else
		    porta_ddr   <= porta_ddr;
		    porta_data  <= porta_data;
			 porta_ctrl  <= porta_ctrl;
		    portb_data  <= portb_data;
		    portb_ddr   <= portb_ddr;
			 portb_ctrl  <= portb_ctrl;
			 portb_write <= '0';
	 end if;
  end if;
end process;
 
---------------------------------
--
-- CA1 Edge detect
--
---------------------------------
ca1_input : process( clk, rst, ca1, ca1_del,
                     ca1_rise, ca1_fall, ca1_edge,
							irqa1, porta_ctrl, porta_read )
begin
  if rst = '1' then
    ca1_del  <= '0';
	 ca1_rise <= '0';
    ca1_fall <= '0';
	 ca1_edge <= '0';
	 irqa1    <= '0';
  elsif clk'event and clk = '0' then
    ca1_del  <= ca1;
    ca1_rise <= (not ca1_del) and ca1;
    ca1_fall <= ca1_del and (not ca1);
	 if ca1_edge = '1' then
	    irqa1 <= '1';
	 elsif porta_read = '1' then
	    irqa1 <= '0';
    else
	    irqa1 <= irqa1;
    end if;
  end if;  
 
  if porta_ctrl(1) = '0' then
	 ca1_edge <= ca1_fall;
  else
	 ca1_edge <= ca1_rise;
  end if;
end process;
 
---------------------------------
--
-- CA2 Edge detect
--
---------------------------------
ca2_input : process( clk, rst, ca2, ca2_del,
                     ca2_rise, ca2_fall, ca2_edge,
							irqa2, porta_ctrl, porta_read )
begin
  if rst = '1' then
    ca2_del  <= '0';
	 ca2_rise <= '0';
    ca2_fall <= '0';
	 ca2_edge <= '0';
	 irqa2    <= '0';
  elsif clk'event and clk = '0' then
    ca2_del  <= ca2;
    ca2_rise <= (not ca2_del) and ca2;
    ca2_fall <= ca2_del and (not ca2);
	 if porta_ctrl(5) = '0' and ca2_edge = '1' then
	    irqa2 <= '1';
	 elsif porta_read = '1' then
	    irqa2 <= '0';
    else
	    irqa2 <= irqa2;
    end if;
  end if;  
 
  if porta_ctrl(4) = '0' then
	 ca2_edge <= ca2_fall;
  else
	 ca2_edge <= ca2_rise;
  end if;
end process;
 
---------------------------------
--
-- CA2 output control
--
---------------------------------
ca2_output : process( clk, rst, porta_ctrl, porta_read, ca1_edge, ca2_out )
begin
  if rst='1' then
    ca2_out <= '0';
  elsif clk'event and clk='0' then
    case porta_ctrl(5 downto 3) is
    when "100" => -- read PA clears, CA1 edge sets
      if porta_read = '1' then
	     ca2_out <= '0';
      elsif ca1_edge = '1' then
	     ca2_out <= '1';
      else
	     ca2_out <= ca2_out;
      end if;
    when "101" => -- read PA clears, E sets
      ca2_out <= not porta_read;
    when "110" =>	-- set low
	   ca2_out <= '0';
    when "111" =>	-- set high
	   ca2_out <= '1';
    when others => -- no change
	   ca2_out <= ca2_out;
    end case;
  end if;
end process;
 
 
---------------------------------
--
-- CB1 Edge detect
--
---------------------------------
cb1_input : process( clk, rst, cb1, cb1_del,
                     cb1_rise, cb1_fall, cb1_edge,
							irqb1, portb_ctrl, portb_read )
begin
  if rst = '1' then
    cb1_del  <= '0';
	 cb1_rise <= '0';
    cb1_fall <= '0';
	 cb1_edge <= '0';
	 irqb1    <= '0';
  elsif clk'event and clk = '0' then
    cb1_del  <= cb1;
    cb1_rise <= (not cb1_del) and cb1;
    cb1_fall <= cb1_del and (not cb1);
	 if cb1_edge = '1' then
	    irqb1 <= '1';
	 elsif portb_read = '1' then
	    irqb1 <= '0';
    else
	    irqb1 <= irqb1;
    end if;
  end if;
 
  if portb_ctrl(1) = '0' then
	 cb1_edge <= cb1_fall;
  else
	 cb1_edge <= cb1_rise;
  end if;
end process;
 
---------------------------------
--
-- CB2 Edge detect
--
---------------------------------
cb2_input : process( clk, rst, cb2, cb2_del,
                     cb2_rise, cb2_fall, cb2_edge,
							irqb2, portb_ctrl, portb_read )
begin
  if rst = '1' then
    cb2_del  <= '0';
	 cb2_rise <= '0';
    cb2_fall <= '0';
	 cb2_edge <= '0';
	 irqb2    <= '0';
  elsif clk'event and clk = '0' then
    cb2_del  <= cb2;
    cb2_rise <= (not cb2_del) and cb2;
    cb2_fall <= cb2_del and (not cb2);
	 if portb_ctrl(5) = '0' and cb2_edge = '1' then
	    irqb2 <= '1';
	 elsif portb_read = '1' then
	    irqb2 <= '0';
    else
	    irqb2 <= irqb2;
    end if;
  end if;
 
  if portb_ctrl(4) = '0' then
	 cb2_edge <= cb2_fall;
  else
	 cb2_edge <= cb2_rise;
  end if;
 
end process;
 
---------------------------------
--
-- CB2 output control
--
---------------------------------
cb2_output : process( clk, rst, portb_ctrl, portb_write, cb1_edge, cb2_out )
begin
  if rst='1' then
    cb2_out <= '0';
  elsif clk'event and clk='0' then
    case portb_ctrl(5 downto 3) is
    when "100" => -- write PB clears, CA1 edge sets
      if portb_write = '1' then
	     cb2_out <= '0';
      elsif cb1_edge = '1' then
	     cb2_out <= '1';
      else
	     cb2_out <= cb2_out;
      end if;
    when "101" => -- write PB clears, E sets
      cb2_out <= not portb_write;
    when "110" =>	-- set low
	   cb2_out <= '0';
    when "111" =>	-- set high
	   cb2_out <= '1';
    when others => -- no change
	   cb2_out <= cb2_out;
    end case;
  end if;
end process;
 
---------------------------------
--
-- IRQ control
--
---------------------------------
pia_irq : process( irqa1, irqa2, irqb1, irqb2, porta_ctrl, portb_ctrl )
begin
  irqa <= (irqa1 and porta_ctrl(0)) or (irqa2 and porta_ctrl(3));
  irqb <= (irqb1 and portb_ctrl(0)) or (irqb2 and portb_ctrl(3));
end process;
 
---------------------------------
--
-- 2 x 74193 binary down counter
--
---------------------------------
--
-- On the reference 6809 board, 
-- RTI takes one more clock cycle than System09
-- So subtract 1 from the porta_data preset value.
-- 11th July 2006 John Kent
-- RTI in CPU09 has been extended by one bus cycle
-- so remove the subtract by one offset on porta_data
--
pia_counter : process( clk, timer, porta_data, ca2_out, cb2_out)
begin
  if cb2_out = '1' then
    timer <= "00000000";
  elsif ca2_out = '0' then
--    timer <= porta_data - "00000001";
    timer <= porta_data;
  elsif clk'event and clk='1' then
    timer <= timer - "00000001";
  end if;
  pa  <= "00000000";
  pb  <= timer;
  ca1 <= timer(7);
  cb1 <= timer(7);
  ca2 <= '0';
  cb2 <= '0';
end process;
 
end pia_arch;