-- Description : Calcul du code RS(204,188,8)
-- Littérature :
-- Lin and Costello, Error Control Coding.
-- Morelos-Zaragoza, The art of error correcting coding.
-- Reed-Solomon RS(204,188,T=8) réduit.
-- issue du code original RS(255,239,T=8).
-- Polynome primitif : p(x) = x^8 + x^4 + x^3 + x^2 + 1.
-- Polynome générateur : G(x)=(x-a^0)(x-a^1)...(x-a^15) over a Galois field of GF(256).
-- All registers are driven by common clock (clk), clock enable (ce), and asynchronous reset (xgsr) signals. This
-- provides ultimate flexibility in integration of the core into larger systems. The registers are clocked on the rising
-- edge of 'clk', enabled by a high on 'ce', and asynchronously reset by a high on 'xgsr'. The 'ce_fec' signal controls
-- whether the core is calculating the parity (high) or shifting out the calculated parity (low).
-- f_rscalcul Blocks perform modulo 2 addition of the input symbols.
-- f_rscalcul Blocks perform a finite field multiplication, over the Galois field, of a constant and the input symbol.
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use work.pkg_util.all;
entity rs_encoder is
port(
xgsr : in std_logic; -- reset global asynchrone
clk : in std_logic; -- horloge de traitement
din : in std_logic_vector(7 downto 0); -- Bus de donnée d'entrée
ce : in std_logic; -- A '1' lorsque les données d'entrées sont valides
start : in std_logic; -- A '1' lors de la présence du premier octet entrant en compte dans le calcul du BIP8
ce_fec : in std_logic; -- A '1' lors du calcul du fec sur des octets d'entrée valident
dout : out std_logic_vector(7 downto 0)); -- données incluant le code correscteur d'erreur
end rs_encoder;
architecture A of rs_encoder is
function f_gfmult(a : std_logic_vector(7 downto 0); b : std_logic_vector(7 downto 0))
return std_logic_vector is
variable result : std_logic_vector(7 downto 0);
begin
result(0) := (b(0) and a(0)) xor (b(1) and a(7)) xor (b(2) and a(6)) xor (b(3) and a(5)) xor (b(4) and a(4)) xor
(b(5) and a(3)) xor (b(5) and a(7)) xor (b(6) and a(2)) xor (b(6) and a(6)) xor (b(6) and a(7)) xor
(b(7) and a(1)) xor (b(7) and a(5)) xor (b(7) and a(6)) xor (b(7) and a(7));
result(1) := (b(0) and a(1)) xor (b(1) and a(0)) xor (b(2) and a(7)) xor (b(3) and a(6)) xor (b(4) and a(5)) xor
(b(5) and a(4)) xor (b(6) and a(3)) xor (b(6) and a(7)) xor (b(7) and a(2)) xor (b(7) and a(6)) xor
(b(7) and a(7));
result(2) := (b(0) and a(2)) xor (b(1) and a(1)) xor (b(1) and a(7)) xor (b(2) and a(0)) xor (b(2) and a(6)) xor
(b(3) and a(5)) xor (b(3) and a(7)) xor (b(4) and a(4)) xor (b(4) and a(6)) xor (b(5) and a(3)) xor
(b(5) and a(5)) xor (b(5) and a(7)) xor (b(6) and a(2)) xor (b(6) and a(4)) xor (b(6) and a(6)) xor
(b(6) and a(7)) xor (b(7) and a(1)) xor (b(7) and a(3)) xor (b(7) and a(5)) xor (b(7) and a(6));
result(3) := (b(0) and a(3)) xor (b(1) and a(2)) xor (b(1) and a(7)) xor (b(2) and a(1)) xor (b(2) and a(6)) xor
(b(2) and a(7)) xor (b(3) and a(0)) xor (b(3) and a(5)) xor (b(3) and a(6)) xor (b(4) and a(4)) xor
(b(4) and a(5)) xor (b(4) and a(7)) xor (b(5) and a(3)) xor (b(5) and a(4)) xor (b(5) and a(6)) xor
(b(5) and a(7)) xor (b(6) and a(2)) xor (b(6) and a(3)) xor (b(6) and a(5)) xor (b(6) and a(6)) xor
(b(7) and a(1)) xor (b(7) and a(2)) xor (b(7) and a(4)) xor (b(7) and a(5));
result(4) := (b(0) and a(4)) xor (b(1) and a(3)) xor (b(1) and a(7)) xor (b(2) and a(2)) xor (b(2) and a(6)) xor
(b(2) and a(7)) xor (b(3) and a(1)) xor (b(3) and a(5)) xor (b(3) and a(6)) xor (b(3) and a(7)) xor
(b(4) and a(0)) xor (b(4) and a(4)) xor (b(4) and a(5)) xor (b(4) and a(6)) xor (b(5) and a(3)) xor
(b(5) and a(4)) xor (b(5) and a(5)) xor (b(6) and a(2)) xor (b(6) and a(3)) xor (b(6) and a(4)) xor
(b(7) and a(1)) xor (b(7) and a(2)) xor (b(7) and a(3)) xor (b(7) and a(7));
result(5) := (b(0) and a(5)) xor (b(1) and a(4)) xor (b(2) and a(3)) xor (b(2) and a(7)) xor (b(3) and a(2)) xor
(b(3) and a(6)) xor (b(3) and a(7)) xor (b(4) and a(1)) xor (b(4) and a(5)) xor (b(4) and a(6)) xor
(b(4) and a(7)) xor (b(5) and a(0)) xor (b(5) and a(4)) xor (b(5) and a(5)) xor (b(5) and a(6)) xor
(b(6) and a(3)) xor (b(6) and a(4)) xor (b(6) and a(5)) xor (b(7) and a(2)) xor (b(7) and a(3)) xor
(b(7) and a(4));
result(6) := (b(0) and a(6)) xor (b(1) and a(5)) xor (b(2) and a(4)) xor (b(3) and a(3)) xor (b(3) and a(7)) xor
(b(4) and a(2)) xor (b(4) and a(6)) xor (b(4) and a(7)) xor (b(5) and a(1)) xor (b(5) and a(5)) xor
(b(5) and a(6)) xor (b(5) and a(7)) xor (b(6) and a(0)) xor (b(6) and a(4)) xor (b(6) and a(5)) xor
(b(6) and a(6)) xor (b(7) and a(3)) xor (b(7) and a(4)) xor (b(7) and a(5));
result(7) := (b(0) and a(7)) xor (b(1) and a(6)) xor (b(2) and a(5)) xor (b(3) and a(4)) xor (b(4) and a(3)) xor
(b(4) and a(7)) xor (b(5) and a(2)) xor (b(5) and a(6)) xor (b(5) and a(7)) xor (b(6) and a(1)) xor
(b(6) and a(5)) xor (b(6) and a(6)) xor (b(6) and a(7)) xor (b(7) and a(0)) xor (b(7) and a(4)) xor
(b(7) and a(5)) xor (b(7) and a(6));
return result;
end f_rscalcul;
-- gin0.....gin15 (8 bits each ) =
-- Generator polynomial co-effcients.
-- The generator polynomial is form X^16 + gin15 X^15 + gin14 X^14 + ...... gin1 X + gin0.
-- Each gi (i=0, 1, ...15) is an element of GF(2^8);
signal gin : Tab_std_vector8(15 downto 0); -- coefficients du polynome générateur
signal fback : std_logic_vector(7 downto 0); -- initialisation ?
signal val_fec : Tab_std_vector8(15 downto 0); -- z dans le code initial
begin
gin(0) <= std_logic_vector(to_unsigned( 59,8)); -- 136 59 x"21" assign GPol1 = 59;
gin(1) <= std_logic_vector(to_unsigned( 36,8)); -- 240 13 x"AB" assign GPol2 = 13;
gin(2) <= std_logic_vector(to_unsigned( 50,8)); -- 208 104 x"21" assign GPol3 = 104;
gin(3) <= std_logic_vector(to_unsigned( 98,8)); -- 195 189 x"8E" assign GPol4 = 189;
gin(4) <= std_logic_vector(to_unsigned(229,8)); -- 181 68 x"93" assign GPol5 = 68;
gin(5) <= std_logic_vector(to_unsigned( 41,8)); -- 158 209 x"AB" assign GPol6 = 209;
gin(6) <= std_logic_vector(to_unsigned( 65,8)); -- 201 30 x"8E" assign GPol7 = 30;
gin(7) <= std_logic_vector(to_unsigned(163,8)); -- 100 8 x"CD" assign GPol8 = 8;
gin(8) <= std_logic_vector(to_unsigned( 8,8)); -- 11 163 x"FA" assign GPol9 = 163;
gin(9) <= std_logic_vector(to_unsigned( 30,8)); -- 83 65 x"EE" assign GPol10 = 65;
gin(10) <= std_logic_vector(to_unsigned(209,8)); -- 167 41 x"FF" assign GPol11 = 41;
gin(11) <= std_logic_vector(to_unsigned( 68,8)); -- 107 229 x"0C" assign GPol12 = 229;
gin(12) <= std_logic_vector(to_unsigned(189,8)); -- 113 98 x"AB" assign GPol13 = 98;
gin(13) <= std_logic_vector(to_unsigned(104,8)); -- 110 50 x"26" assign GPol14 = 50;
gin(14) <= std_logic_vector(to_unsigned( 13,8)); -- 106 36 x"35" assign GPol15 = 36;
gin(15) <= std_logic_vector(to_unsigned( 59,8)); -- 121 59 x"89" assign GPol16 = 59;
fback <= (val_fec(15) xor din) when (ce_fec='1') else (others => '0');
cal_rs_proc: process(xgsr,clk)
begin
if (xgsr ='1') then
for i in 0 to 15 loop
val_fec(i) <= (others =>'0');
end loop;
dout <= (others =>'0');
elsif rising_edge(clk) then
if (ce='1') then
-- val_fec = x^(n-k).u(x).mod[g(x)]
val_fec(0) <= f_gfmult(fback, gin(0));
for i in 1 to 15 loop
val_fec(i) <= val_fec(i-1) xor f_gfmult(fback, gin(i));
end loop;
-- mux output control : k information symbol and n-k parity
if (ce_fec='1') then
dout <= din;
else
dout <= val_fec(15);
end if;
end if;
end if;
end process cal_rs_proc;
end A;
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