Code for Hamming Distance Transmission & Reception.

--Program for HAMMING CODE TRANSMISSION &  RECEPTION .
-- ( generating Hamming code parellely , ssending it serially &
-- receiving it parallely for error detecttion & correction.)
--(IMPORTANT:- ASSIGN THAT PIN OF THE CPLDD TO THE CLK I/P BY WHICH YOU CAN TOGGLE THE 
-- CLOCK WITH A SWITCH PROVIDED ON THE CPLLD BOARD.)

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.all;                                                                                                                                        
entity hammgen is
port (
d: in STD_LOGIC_VECTOR (3 downto 0); -- i/p message bits
clk:in STD_LOGIC; -- Clock i/p
ten:in STD_LOGIC; -- transmitter-enable(Mux enable)
err:in STD_LOGIC; -- error introducing i/p 
ren:in STD_LOGIC; -- receiver-enable(Demux enable)
dh: out STD_LOGIC_VECTOR (7 downto 1); --Detected & corrected Hamming code.
error:out STD_LOGIC_VECTOR (6 downto 0) -- 7-segment o/p for displaying error.
);
end hammgen;

architecture hammgen_arch of hammgen is
signal h: STD_LOGIC_VECTOR (7 downto 1);
signal mh :STD_LOGIC; 
signal dmh:STD_LOGIC_VECTOR(7 downto 1);
signal sipoh: STD_LOGIC_VECTOR (7 downto 1);
signal ripoh: STD_LOGIC_VECTOR (7 downto 1);
signal sum1 : STD_LOGIC;
signal sum2 : STD_LOGIC;
signal sum4 : STD_LOGIC;
signal p1 : STD_LOGIC;
signal p2: STD_LOGIC;
signal p4 : STD_LOGIC;
signal en: STD_LOGIC_VECTOR (7 downto 1);
signal sum5: STD_LOGIC;
signal sum6: STD_LOGIC;
signal sum8: STD_LOGIC;
signal y: STD_LOGIC_VECTOR (7 downto 0); 
signal countx:STD_LOGIC_VECTOR (2 downto 0);
signal countr:STD_LOGIC_VECTOR (2 downto 0);

begin
-- Program module for HAMMING CODE GENERATTION .

process (sum1,sum2,sum4,p1,p2,p4,d)
  begin
      sum1<=d(0) xor d(1) xor d(3); -- Parity bits are found here. 
      sum2<=d(0) xor d(2) xor d(3); 
      sum4<=d(1) xor d(2) xor d(3);
      if sum1='0' then
         p1<='0';
     else 
         p1<='1'; 
     end if;

     if sum2='0' then
        p2<='0'; 
    else 
        p2<='1'; 
    end if;

    if sum4='0' then
       p4<='0';
   else 
       p4<='1'; 
   end if;
end process;

h(1)<=p1; --The parity bits found out in the above process block
h(2)<=p2; -- are put in a register 'h'(declared as signal). 
h(3)<=d(0);
h(4)<=p4;
h(5)<=d(1);
h(6)<=d(2);
h(7)<=d(3);

-- Program module for Mux & xmit count & iintroducing error. 

process (clk,countx,ten) -- A 3-bit up counter o/p (countx) is connected
   begin -- to the Select lines of the Mux which will 
       if clk 'event and clk='1' then -- increment the ststus of the Select lines 
          if ten='1' then -- automatically . 
             if (countx <"111"or countx="111") then
                countx<=countx+1;
            else
                countx<="000";
           end if; 
        else
             countx<="ZZZ"; 
       end if; 
    end if;
end process;

process(countx,clk,h,err,mh) -- In this part the Hamming code bits are sent
    begin -- thro' the Mux . If the err i/p is =1 error 
         if clk'event and clk='1' then -- is introduced in the hamming code bit (means
            case countx is -- that bit is complemented.) 
                    when "000"=> -- mh is Mux o/p. 
                             if err='0' then
                                mh<=h(7);
                             else
                                mh<=not h(7);
                             end if; 
                    when "001"=>mh<=h(6);
                             if err='0' then
                                mh<=h(6);
                             else
                                mh<=not h(6);
                             end if; 
                    when "010"=>mh<=h(5);
                             if err='0' then
                                mh<=h(5);
                            else
                                mh<=not h(5);
                            end if; 
                  when "011"=>mh<=h(4);
                            if err='0' then
                               mh<=h(4);
                            else
                               mh<=not h(4);
                            end if;  
                  when "100"=>mh<=h(3);
                            if err='0' then
                               mh<=h(3);
                            else
                               mh<=not h(3);
                            end if; 
                  when "101"=>mh<=h(2);
                            if err='0' then
                               mh<=h(2);
                            else
                               mh<=not h(2);
                            end if; 
                  when "110"=>mh<=h(1);
                            if err='0' then 
                               mh<=h(1);
                            else
                               mh<=not h(1);
                            end if; 
                  when others=>Null;
          end case;
        end if; 
    end process;

-- Program module for De-mux & rec. count  .

process(ren,clk,countr,mh) --process(r,clk,ren,ch,countr)
begin
if clk 'event and clk='1' then -- A 3 bit counter o/p 
if ren='1' then -- similar to the mux,
if ( countr<"111"or countr="111" ) then -- is given to the select
countr<=countr+1; -- lines. 

dmh<=mh&dmh(7 downto 2) ; -- Here serial to parellel 
else -- conversion of the received 
countr<="000"; -- serial hamming code from the 
-- mux(i.e. mh signal), is made. 
end if; --(Shift register concept)
else
countr<="ZZZ"; 
dmh<="ZZZZZZZ"; 
end if;
end if;
end process;
sipoh<=dmh; -- When the serial data (mh) is shifted to make it parallel
-- the MSB goes into the LSB position. So  the shifted bits
-- of dmh(Demux o/p) which are stored in ssipoh register
ripoh(7)<=sipoh(1); -- (declared as signal) are put into the ripoh register 
ripoh(6)<=sipoh(2); -- (declared as signal) in reverse order.
ripoh(5)<=sipoh(3);
ripoh(4)<=sipoh(4);
ripoh(3)<=sipoh(5);
ripoh(2)<=sipoh(6);
ripoh(1)<=sipoh(7);

-- Program for HAMMING CODE DETECTION .

sum5<=ripoh(1) xor ripoh(3) xor ripoh(5) xor ripoh(7); -- Error detection part
sum6<=ripoh(2) xor ripoh(3) xor ripoh(6) xor ripoh(7);
sum8<=ripoh(4) xor ripoh(5) xor ripoh(6) xor ripoh(7);


y(0)<=not sum8 and not sum6 and not sum5; -- Decoder is used to decode
y(1)<=not sum8 and not sum6 and sum5; -- the position of the bit in error.
y(2)<=not sum8 and sum6 and not sum5;
y(3)<=not sum8 and sum6 and sum5;
y(4)<= sum8 and not sum6 and not sum5;
y(5)<= sum8 and not sum6 and sum5;
y(6)<= sum8 and sum6 and not sum5;
y(7)<= sum8 and sum6 and sum5;


en(1)<=y(1); -- The decoder o/p lines are given to the
en(2)<=y(2); -- enable (en, which is declared as a signal) i/p
en(3)<=y(3); -- of an inverter so as to complement the bit in
en(4)<=y(4); -- in error. Complementing is done in the next 
en(5)<=y(5); -- process block .
en(6)<=y(6);
en(7)<=y(7);

process( en,ripoh)
begin
case en is
-- 7654321
when "0000001"=>dh<=ripoh(7 downto 2)& not ripoh(1); -- Only the bit in error is complemented
when "0000010"=>dh<=ripoh(7 downto 3)& not ripoh(2)& ripoh(1); -- Rest are kept unchanged.
when "0000100"=>dh<=ripoh(7 downto 4)& not ripoh(3)& ripoh(2 downto 1);
when "0001000"=>dh<=ripoh(7 downto 5)& not ripoh(4)&ripoh(3 downto 1);
when "0010000"=>dh<=ripoh(7 downto 6 )& not ripoh(5)& ripoh(4 downto 1);
when "0100000"=>dh<=ripoh(7)& not ripoh(6)& ripoh(5 downto 1) ;
when "1000000"=>dh<=not ripoh(7)&ripoh(6 downto 1);
when "0000000"=>dh<=ripoh;
when others=>Null;
end case;

end process; 

process(y,countr) --For displaying the error bit position
begin --After all the hamming code bits (mh signal, 
if countr="000" then --i.e. the Mux o/p) , the error bit position
case y is --will be displayed. Else, 3 dashes will be
-- 76543210 -- abcdefg -- shown (means seggments a,g&d will glow.) 
when "00000001" =>error<="1001001"; -- When there is no error (i.e. when y=00000001)
when "00000010" =>error<="0110000"; -- then also three dashes will be shown .
when "00000100" =>error<="1101101";
when "00001000" =>error<="1111001";
when "00010000" =>error<="0110011";
when "00100000" =>error<="1011011";
when "01000000" =>error<="0011111";
when "10000000" =>error<="1110000";
when others =>error<="1000110";
end case;
else
error<="1001001";
end if; 
end process;

end hammgen_arch;