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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;