------------------------------------------------------------------------------- -- Title : 8b10b decoder ------------------------------------------------------------------------------- -- File : an8b10b_decoder.vhd ------------------------------------------------------------------------------- -- Description: Decodes 8b10b encoding, outputs 8bit. Expects aligned characters -- at input. Outputs do_char with disparity error and missing (not in table) errors. -- For first character it's possible to get a disparity error. ------------------------------------------------------------------------------- library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_misc.all; use ieee.numeric_std.all; use work.data_link_pkg.all; entity an8b10b_decoder is port ( ci_char_clk : in std_logic; -- The character clock ci_reset : in std_logic; -- The reset (asynchronous active low) di_10b : in std_logic_vector(9 downto 0); -- The 8b10b encoded input data do_char : out character_vector; -- The output decoded 8b data co_error : out std_logic); -- Whether there is an error (disparity -- or missing) end entity an8b10b_decoder; architecture a1 of an8b10b_decoder is type a5b6b_array is array (0 to 63) of std_logic_vector(4 downto 0); type a3b4b_array is array (0 to 15) of std_logic_vector(2 downto 0); constant a5b6b_alphabet : a5b6b_array := ( 39 => "00000", 24 => "00000", 29 => "00001", 34 => "00001", 45 => "00010", 18 => "00010", 49 => "00011", 53 => "00100", 10 => "00100", 41 => "00101", 25 => "00110", 56 => "00111", 7 => "00111", 57 => "01000", 6 => "01000", 37 => "01001", 21 => "01010", 52 => "01011", 13 => "01100", 44 => "01101", 28 => "01110", 23 => "01111", 40 => "01111", 27 => "10000", 36 => "10000", 35 => "10001", 19 => "10010", 50 => "10011", 11 => "10100", 42 => "10101", 26 => "10110", 58 => "10111", 5 => "10111", 51 => "11000", 12 => "11000", 38 => "11001", 22 => "11010", 54 => "11011", 9 => "11011", 14 => "11100", 46 => "11101", 17 => "11101", 30 => "11110", 33 => "11110", 43 => "11111", 20 => "11111", others => (others => '0')); -- Alphabet for decoding 5b6b code constant a3b4b_alphabet : a3b4b_array := ( 4 => "000", 11 => "000", 9 => "001", 5 => "010", 3 => "011", 12 => "011", 2 => "100", 13 => "100", 10 => "101", 6 => "110", 1 => "111", 14 => "111", 8 => "111", 7 => "111", others => (others => '0')); -- Alphabet for decoding 3b4b code constant ctrl_3b4b_alphabet : a3b4b_array := ( 4 => "000", 9 => "001", 5 => "010", 3 => "011", 2 => "100", 10 => "101", 6 => "110", 8 => "111", others => (others => '0')); -- Alphabet for decoding control 3b4b code constant ctrl_5b6b_alphabet : a5b6b_array := ( 15 => "11100", 58 => "10111", 54 => "11011", 46 => "11101", 30 => "11110", others => (others => '0')); -- Alphabet for decoding control 5b6b code signal reg_do_8b : std_logic_vector(7 downto 0) := (others => '0'); signal reg_rd : std_logic := '0'; -- The current running disparity -- (0 for RD = -1) signal next_disparity_error : std_logic; signal next_missing_error : std_logic; signal next_error : std_logic; signal next_kout : std_logic := '0'; signal next_rd : std_logic := '0'; signal change_rd : std_logic := '0'; signal next_do_8b : std_logic_vector(7 downto 0) := (others => '0'); signal data_4b : std_logic_vector(3 downto 0) := "0000"; signal data_6b : std_logic_vector(5 downto 0) := "000000"; signal data_4b_int : integer range 0 to 15 := 0; signal data_6b_int : integer range 0 to 63 := 0; signal data_4b_int_neg : integer range 0 to 15 := 0; signal data_6b_int_neg : integer range 0 to 63 := 0; function IsMissingCharacter( cdata_4b_int : integer range 0 to 15; cdata_6b_int : integer range 0 to 63 ) return std_logic is variable d : std_logic; begin if cdata_4b_int = 0 or cdata_4b_int = 15 then return '1'; end if; if cdata_6b_int < 5 then return '1'; end if; if cdata_6b_int > 58 then return '1'; end if; if cdata_6b_int = 8 or cdata_6b_int = 16 or cdata_6b_int = 47 or cdata_6b_int = 55 then return '1'; end if; return '0'; end function; function IsControlCharacter ( data : std_logic_vector(9 downto 0)) return std_logic is begin if data(9 downto 4) = "001111" or data(9 downto 4) = "110000" then return '1'; end if; if data = "1110101000" or data = "1101101000" or data = "1011101000" or data = "0111101000" then return '1'; end if; if data = not "1110101000" or data = not "1101101000" or data = not "1011101000" or data = not "0111101000" then return '1'; end if; return '0'; end function; function IsDisparityCorrect ( cdata_4b : std_logic_vector(3 downto 0); cdata_6b : std_logic_vector(5 downto 0); rd : std_logic) return std_logic is variable ones_6b : integer range 0 to 63 := 0; variable ones_4b : integer range 0 to 15 := 0; variable correct_rd : std_logic; begin -- function IsDisparityCorrect correct_rd := rd; for i in 0 to 5 loop if cdata_6b(i) = '1' then ones_6b := ones_6b + 1; end if; if i < 4 and cdata_4b(i) = '1' then ones_4b := ones_4b + 1; end if; end loop; -- i if ones_6b + ones_4b > 6 or ones_6b + ones_4b < 4 then return '0'; end if; if ones_6b > 3 then correct_rd := '0'; elsif ones_6b < 3 then correct_rd := '1'; else if ones_4b > 2 then correct_rd := '0'; elsif ones_4b < 2 then correct_rd := '1'; else if cdata_6b = "000111" then correct_rd := '1'; elsif cdata_6b = "111000" then correct_rd := '0'; elsif cdata_4b = "0011" then correct_rd := '1'; elsif cdata_4b = "1100" then correct_rd := '0'; end if; end if; end if; if correct_rd = rd then return '1'; else return '0'; end if; end function IsDisparityCorrect; begin -- architecture a1 -- purpose: Set next states -- type : sequential -- inputs : ci_char_clk, ci_reset -- outputs: co_error, co_disparity_error, co_missing_error, reg_do_8b, -- reg_rd, co_kout set_next: process (ci_char_clk, ci_reset) is begin -- process set_next if ci_reset = '0' then -- asynchronous reset (active low) co_error <= '0'; do_char.disparity_error <= '0'; do_char.missing_error <= '0'; do_char.kout <= '0'; do_char.user_data <= '0'; reg_do_8b <= (others => '0'); reg_rd <= '0'; elsif ci_char_clk'event and ci_char_clk = '1' then -- rising clock edge co_error <= next_error; do_char.disparity_error <= next_disparity_error; do_char.missing_error <= next_missing_error; do_char.kout <= next_kout; do_char.user_data <= '0'; reg_do_8b <= next_do_8b; reg_rd <= next_rd; end if; end process set_next; data_4b <= di_10b(3 downto 0); data_6b <= di_10b(9 downto 4); data_4b_int <= to_integer(unsigned(data_4b)); data_6b_int <= to_integer(unsigned(data_6b)); data_4b_int_neg <= to_integer(unsigned(not data_4b)); data_6b_int_neg <= to_integer(unsigned(not data_6b)); -- running disparity -- change in case the number of 0s doesn't match nubmer of 1s (xor_reduce -- will output 1 ... it's basically an odd parity) -- synchronize in case of disparity error (can be either at the beginning of -- communication or the last character was loaded incorrectly) change_rd <= (not xor_reduce(di_10b) or next_disparity_error) and not (not xor_reduce(di_10b) and next_disparity_error); next_rd <= (not reg_rd and change_rd) or (reg_rd and not change_rd); -- control characters next_kout <= IsControlCharacter(di_10b); -- errors next_missing_error <= IsMissingCharacter(data_4b_int, data_6b_int) and not next_kout; next_disparity_error <= not IsDisparityCorrect(data_4b, data_6b, reg_rd); next_error <= next_missing_error or next_disparity_error; next_do_8b <= a3b4b_alphabet(data_4b_int) & a5b6b_alphabet(data_6b_int) when next_kout = '0' else ctrl_3b4b_alphabet(data_4b_int_neg) & ctrl_5b6b_alphabet(data_6b_int_neg) when (reg_rd = '1' and next_disparity_error = '0') else ctrl_3b4b_alphabet(data_4b_int) & ctrl_5b6b_alphabet(data_6b_int) when (reg_rd = '1' or next_disparity_error = '0') else ctrl_3b4b_alphabet(data_4b_int_neg) & ctrl_5b6b_alphabet(data_6b_int_neg); do_char.d8b <= reg_do_8b; end architecture a1;