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--************************************************************************************************

-- Internal I/O registers (implemented inside the core) decoder/multiplexer 

-- for AVR core

-- Version 1.3 (Special version for the JTAG OCD)

-- Designed by Ruslan Lepetenok

-- Modified 22.04.2004

--************************************************************************************************

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.std_logic_unsigned.all;

use WORK.AVRuCPackage.all;

entity io_reg_file is port (

                                    --Clock and reset

                                cp2           : in std_logic;

                                                        cp2en         : in std_logic;

                            ireset        : in std_logic;

                            adr           : in std_logic_vector(5 downto 0);

                            iowe          : in std_logic;

                            dbusout       : in std_logic_vector(7 downto 0);

                            sreg_fl_in    : in std_logic_vector(7 downto 0);

                            sreg_out      : out std_logic_vector(7 downto 0);

                            sreg_fl_wr_en : in  std_logic_vector (7 downto 0);   --FLAGS WRITE ENABLE SIGNALS       

                            spl_out       : out std_logic_vector(7 downto 0);

                            sph_out       : out std_logic_vector(7 downto 0);

                            sp_ndown_up   : in std_logic; -- DIRECTION OF CHANGING OF STACK POINTER SPH:SPL 0->UP(+) 1->DOWN(-)

                            sp_en         : in std_logic; -- WRITE ENABLE(COUNT ENABLE) FOR SPH AND SPL REGISTERS

                            rampz_out    : out std_logic_vector(7 downto 0));

end io_reg_file;

architecture rtl of io_reg_file is

signal sreg    : std_logic_vector(7 downto 0);

signal sph     : std_logic_vector(7 downto 0);

signal spl     : std_logic_vector(7 downto 0);

signal rampz   : std_logic_vector(7 downto 0);

signal sp_int  : std_logic_vector(15 downto 0);

signal sp_intp : std_logic_vector(15 downto 0);

signal sp_intm : std_logic_vector(15 downto 0);

signal sp_res : std_logic_vector(15 downto 0);

begin

sreg_write:process(cp2,ireset)

begin

if ireset='0' then

sreg <= (others => '0');

elsif (cp2='1' and cp2'event) then

 if (cp2en='1') then                                                      -- Clock enable       

  for i in sreg'range loop

   if (sreg_fl_wr_en(i)='1' or (adr=SREG_Address and iowe='1')) then    -- CLOCK ENABLE

    if iowe='1' then

     sreg(i) <= dbusout(i);                        -- FROM THE INTERNAL DATA BUS

    else

     sreg(i) <= sreg_fl_in(i);                  -- FROM ALU FLAGS

    end if;

   end if;

  end loop;

 end if;

end if;

end process;

sreg_out <= sreg;

sp_intp<=(sph&spl)+1;

sp_intm<=(sph&spl)-1;

sp_res<= sp_intm when sp_ndown_up='0' else sp_intp;

spl_write:process(cp2,ireset)

begin

if ireset='0' then

spl <= (others => '0');

elsif (cp2='1' and cp2'event) then

if (sp_en='1' or (adr=SPL_Address and iowe='1')) then    -- CLOCK ENABLE

 if iowe='1' then

  spl <= dbusout;                                        -- FROM THE INTERNAL DATA BUS

   else

    spl <= sp_res(7 downto 0);                          -- FROM SPL BUS

     end if;

 end if;

end if;

end process;

spl_out <= spl;

sph_write:process(cp2,ireset)

begin

if ireset='0' then

sph <= (others => '0');

elsif (cp2='1' and cp2'event) then

if (sp_en='1' or (adr=SPH_Address and iowe='1')) then    -- CLOCK ENABLE

 if iowe='1' then

  sph <= dbusout;                        -- FROM THE INTERNAL DATA BUS

   else

    sph <= sp_res(15 downto 8);                          -- FROM SPH BUS

     end if;

 end if;

end if;

end process;

sph_out <= sph;

rampz_write:process(cp2,ireset)

begin

if ireset='0' then

rampz <= (others => '0');

elsif (cp2='1' and cp2'event) then

if (adr=RAMPZ_Address and iowe='1') then    -- CLOCK ENABLE

  rampz <= dbusout;                      -- FROM THE INTERNAL DATA BUS

 end if;

end if;

end process;

rampz_out <= rampz;

end rtl;