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-- 

--
--  FRAME_CHECK
--
--
--
--  Description: This module is a  pattern checker to test the Aurora
--               designs in hardware. The frames generated by FRAME_GEN
--               pass through the Aurora channel and arrive at the frame checker 
--               through the RX User interface. Every time an error is found in
--               the data recieved, the error count is incremented until it 
--               reaches its max value.


library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.NUMERIC_STD.all;
use IEEE.STD_LOGIC_ARITH.all;
use IEEE.STD_LOGIC_UNSIGNED.all;
use WORK.AURORA_PKG.all; 

-- synthesis translate_off
library UNISIM;
use UNISIM.all;
-- synthesis translate_on


entity aurora_8b10b_v5_2_FRAME_CHECK is
port
(
    -- User Interface
    RX_D            : in  std_logic_vector(0 to 15); 
    RX_REM          : in  std_logic;     
    RX_SOF_N        : in  std_logic;
    RX_EOF_N        : in  std_logic;
    RX_SRC_RDY_N    : in  std_logic;


    -- System Interface
    USER_CLK        : in  std_logic;   
    RESET           : in  std_logic;
    CHANNEL_UP      : in  std_logic;
    ERR_COUNT       : out std_logic_vector(0 to 7)
  
);
end aurora_8b10b_v5_2_FRAME_CHECK;



architecture RTL of aurora_8b10b_v5_2_FRAME_CHECK is

--***********************************Parameter Declarations***************************

    constant DLY : time := 1 ns;

--***************************Internal Register Declarations*************************** 
    signal  tied_to_ground           :   std_logic_vector(7 downto 0);
    signal  reset_c                  :   std_logic;
    signal  data_in_frame_r          :   std_logic;
    signal  data_valid_r             :   std_logic;
    signal  pdu_cmp_data_r           :   std_logic_vector(0 to 15);
    signal  RX_D_R                   :   std_logic_vector(0 to 15);

    signal  data_lfsr_r              :   std_logic_vector(0 to 15);
    signal  data_err_detected_c    :   std_logic;
    signal  data_err_detected_r    :   std_logic;
    --temporary signal for ERR_COUNT
    signal  err_count_tmp          :   std_logic_vector(0 to 8);
    
    signal  data_valid_c             :   std_logic;
    signal  data_in_frame_c          :   std_logic;
    
    signal  data_lfsr_concat_w       :   std_logic_vector(0 to 15);


begin
--*********************************Main Body of Code**********************************

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

    --Generate RESET signal when Aurora channel is not ready
    reset_c <= RESET or not CHANNEL_UP;

    --______________________________ Capture incoming data ___________________________    
    --Data is valid when RX_SRC_RDY_N is asserted and data is arriving within a frame
    data_valid_c    <=   data_in_frame_c and not RX_SRC_RDY_N;

    --Data is in a frame if it is a single cycle frame or a multi_cycle frame has started
    data_in_frame_c      <=   data_in_frame_r  or  (not RX_SRC_RDY_N and not RX_SOF_N);

    --RX Data in the pdu_cmp_data_r register is valid 
    --only if it was valid when captured and had no error
    process(USER_CLK)
    begin
        if(USER_CLK'event and USER_CLK = '1') then
            if(reset_c = '1') then
                data_valid_r    <=  '0' after DLY;
            else
                data_valid_r    <=  data_valid_c and not data_err_detected_c after DLY;
            end if;
        end if;
    end process;
    
    --Start a multicycle frame when a frame starts without ending on the same cycle. End 
    --the frame when an EOF is detected
    process(USER_CLK)
    begin
        if(USER_CLK'event and USER_CLK = '1') then
            if(reset_c = '1') then   
                data_in_frame_r  <=  '0' after DLY;
            elsif((not data_in_frame_r and not RX_SOF_N and not RX_SRC_RDY_N and RX_EOF_N)='1') then
                data_in_frame_r  <=  '1' after DLY;
            elsif((data_in_frame_r and not RX_SRC_RDY_N and not RX_EOF_N)='1') then
                data_in_frame_r  <=  '0' after DLY;
            end if;
        end if;
    end process;

    --Register and decode the RX_D data with RX_REM bus      
    process(USER_CLK)
    begin
      if(USER_CLK'event and USER_CLK = '1') then
        if((not RX_EOF_N and not RX_SRC_RDY_N) = '1') then
          case RX_REM is
            when '0' => RX_D_R <= (RX_D(0 to 7) & tied_to_ground(7 downto 0)) after DLY;
            when '1' => RX_D_R <= RX_D after DLY; 
            when others => RX_D_R <= RX_D after DLY; 		 
          end case; 	 
        elsif(RX_SRC_RDY_N = '0') then
          RX_D_R <= RX_D after DLY;
        end if;
      end if;
    end process;

    --Calculate the expected frame data     
    process(USER_CLK)
    begin
      if(USER_CLK'event and USER_CLK = '1') then
        if(reset_c = '1') then
          pdu_cmp_data_r <= (X"D5E6") after DLY;
        elsif((data_valid_c and not RX_EOF_N) = '1') then
          case RX_REM is
            when '0' => pdu_cmp_data_r <= (data_lfsr_concat_w(0 to 7) & tied_to_ground(7 downto 0)) after DLY;
            when '1' => pdu_cmp_data_r <= data_lfsr_concat_w after DLY; 
            when others => pdu_cmp_data_r <= data_lfsr_concat_w after DLY; 		 
          end case; 	 
        elsif(data_valid_c = '1') then
          pdu_cmp_data_r <= data_lfsr_concat_w after DLY; 	
        end if;
      end if;
    end process;
                

    --generate expected RX_D using Data LFSR
    process(USER_CLK)
    begin
        if(USER_CLK'event and USER_CLK='1') then
            if(reset_c = '1') then
                data_lfsr_r     <=  X"D5E6" after DLY;  --random seed value
            elsif(data_valid_c='1') then
                data_lfsr_r <= (not(data_lfsr_r(3) xor data_lfsr_r(12) xor data_lfsr_r(14) xor data_lfsr_r(15)) & 
                                data_lfsr_r(0 to 14)) after DLY;
            end if;
        end if;
    end process; 
  
    data_lfsr_concat_w <= (data_lfsr_r); 

    
    --___________________________ Check incoming data for errors __________________________
    --An error is detected when LFSR generated RX data from the pdu_cmp_data_r register, 
    --does not match valid data from the RX_D port
    data_err_detected_c    <= (data_valid_r and std_bool(RX_D_R /= pdu_cmp_data_r)); 

    --We register the data_err_detected_c signal for use with the error counter logic
    process(USER_CLK)
    begin
        if(USER_CLK'event and USER_CLK = '1') then
          data_err_detected_r    <=  data_err_detected_c after DLY;
        end if;
    end process;
   
    --Compare the incoming data with calculated expected data.
    --Increment the ERROR COUNTER if mismatch occurs.
    --Stop the ERROR COUNTER once it reaches its max value (i.e. 255)    
    process(USER_CLK)
    begin
      if(USER_CLK'event and USER_CLK = '1') then
        if(reset_c = '1') then
          err_count_tmp <= (others => '0') after DLY;
        elsif(err_count_tmp = X"1FF") then
          err_count_tmp <= err_count_tmp after DLY;
        elsif((data_err_detected_r ) = '1') then
          err_count_tmp <= err_count_tmp + 1 after DLY;  
        end if;
      end if;
    end process;

    --Here we connect the lower 8 bits of the count (the MSbit is used only to check when the counter reaches
    --max value) to the module output
    ERR_COUNT <= err_count_tmp(1 to 8);

end RTL;
