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

-- "Bit processor" for AVR core

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

-- Designed by Ruslan Lepetenok

-- Modified 29.08.2003

-- Unused inputs(sreg_bit_num[2..0],idc_sbi,idc_cbi,idc_bld) was removed.

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

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.std_logic_unsigned.all;

entity bit_processor is port(

                                                          --Clock and reset

                              cp2             : in  std_logic;

                                                          cp2en           : in  std_logic;

                              ireset          : in  std_logic;

                              bit_num_r_io    : in  std_logic_vector(2 downto 0); -- BIT NUMBER FOR CBI/SBI/BLD/BST/SBRS/SBRC/SBIC/SBIS INSTRUCTIONS

                              dbusin          : in  std_logic_vector(7 downto 0); -- SBI/CBI/SBIS/SBIC  IN

                              bitpr_io_out    : out std_logic_vector(7 downto 0); -- SBI/CBI OUT        

                              sreg_out        : in  std_logic_vector(7 downto 0); -- BRBS/BRBC/BLD IN 

                              branch          : in  std_logic_vector(2 downto 0); -- NUMBER (0..7) OF BRANCH CONDITION FOR BRBS/BRBC INSTRUCTION

                              bit_pr_sreg_out : out std_logic_vector(7 downto 0); -- BCLR/BSET/BST(T-FLAG ONLY)             

                              bld_op_out      : out std_logic_vector(7 downto 0); -- BLD OUT (T FLAG)

                              reg_rd_out      : in  std_logic_vector(7 downto 0); -- BST/SBRS/SBRC IN    

                              bit_test_op_out : out std_logic;                    -- OUTPUT OF SBIC/SBIS/SBRS/SBRC/BRBC/BRBS

                              -- Instructions and states

                              sbi_st          : in  std_logic;

                              cbi_st          : in  std_logic;

                              idc_bst         : in  std_logic;

                              idc_bset        : in  std_logic;

                              idc_bclr        : in  std_logic;

                              idc_sbic        : in  std_logic;

                              idc_sbis        : in  std_logic;

                              idc_sbrs        : in  std_logic;

                              idc_sbrc        : in  std_logic;

                              idc_brbs        : in  std_logic;

                              idc_brbc        : in  std_logic;

                              idc_reti        : in  std_logic

                                                          );

end bit_processor;

architecture RTL of bit_processor is

signal sreg_t_flag     : std_logic;                      --  FOR  BLD INSTRUCTION

signal temp_in_data    : std_logic_vector(7 downto 0);

signal sreg_t_temp     : std_logic_vector(7 downto 0);

signal bit_num_decode   : std_logic_vector(7 downto 0);

signal bit_pr_sreg_out_int : std_logic_vector(7 downto 0);

-- SBIS/SBIC/SBRS/SBRC SIGNALS

signal bit_test_in      : std_logic_vector(7 downto 0);

signal bit_test_mux_out : std_logic_vector(7 downto 0);

-- BRBS/BRBC SIGNALS

signal branch_decode    : std_logic_vector(7 downto 0);

signal branch_mux       : std_logic_vector(7 downto 0);

begin

sreg_t_flag <= sreg_out(6);

-- SBI/CBI STORE REGISTER

sbi_cbi:process(cp2,ireset)

begin

if ireset='0' then

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

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

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

  temp_in_data <= dbusin;

 end if;

end if;

end process;

sbi_cbi_logic:for i in dbusin'range generate

bitpr_io_out(i) <= '1' when (sbi_st='1' and bit_num_decode(i)='1') else  -- SBI

                                   '0' when (cbi_st='1' and bit_num_decode(i)='1') else   -- CBI

                                   temp_in_data(i);                                                                          -- ???

end generate;

-- ########################################################################################

-- BST PART (LOAD T BIT OF SREG FROM THE GENERAL PURPOSE REGISTER)

bit_num_decode_logic:for i in bit_num_decode'range generate

bit_num_decode(i) <= '1' when (i=bit_num_r_io) else '0';

end generate;

sreg_t_temp(0) <= reg_rd_out(0) when bit_num_decode(0)='1' else '0';

bld_logic:for i in 1 to 7 generate

sreg_t_temp(i)<= reg_rd_out(i) when bit_num_decode(i)='1' else sreg_t_temp(i-1);

end generate;

-- BLD LOGIC

bld_inst:for i in reg_rd_out'range generate

bld_op_out(i) <= sreg_t_flag when (i=bit_num_r_io) else reg_rd_out(i);

end generate;

-- ########################################################################################

-- BCLR/BSET/BST/RETI LOGIC

bclr_bset_logic:for i in 0 to 6 generate

bit_pr_sreg_out_int(i) <= (idc_bset and not reg_rd_out(i)) or (not idc_bclr and reg_rd_out(i));

end generate;

-- SREG REGISTER BIT 7 - INTERRUPT ENABLE FLAG

bit_pr_sreg_out_int(7) <= (idc_bset and not reg_rd_out(7)) or (not idc_bclr and reg_rd_out(7)) or idc_reti;

bit_pr_sreg_out <= bit_pr_sreg_out_int(7)&sreg_t_temp(7)&bit_pr_sreg_out_int(5 downto 0) when (idc_bst='1')

                                                                                   else bit_pr_sreg_out_int;

-- SBIC/SBIS/SBRS/SBRC LOGIC

bit_test_in <= dbusin when (idc_sbis='1' or idc_sbic='1') else reg_rd_out;

bit_test_mux_out(0) <= bit_test_in(0) when bit_num_decode(0)='1' else '0';

it_test_mux:for i in 1 to 7 generate

bit_test_mux_out(i)<= bit_test_in(i) when bit_num_decode(i)='1' else bit_test_mux_out(i-1);

end generate;

bit_test_op_out <= (bit_test_mux_out(7) and (idc_sbis or idc_sbrs)) or

                   (not bit_test_mux_out(7) and (idc_sbic or idc_sbrc)) or

                   (branch_mux(7) and idc_brbs) or

                   (not branch_mux(7) and idc_brbc);

-- BRBS/BRBC LOGIC

branch_decode_logic:for i in branch_decode'range generate

branch_decode(i) <= '1' when (i=branch) else '0';

end generate;

branch_mux(0) <= sreg_out(0) when branch_decode(0)='1' else '0';

branch_mux_logic:for i in 1 to 7 generate

branch_mux(i)<= sreg_out(i) when branch_decode(i)='1' else branch_mux(i-1);

end generate;

end RTL;