AtomBusMon/src/AVR8/Core/bit_processor.vhd

--************************************************************************************************
-- "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;