// Chuck Benz, Hollis, NH   Copyright (c)2002
//
// The information and description contained herein is the
// property of Chuck Benz.
//
// Permission is granted for any reuse of this information
// and description as long as this copyright notice is
// preserved.  Modifications may be made as long as this
// notice is preserved.

// per Widmer and Franaszek


module decode_8b10b (datain, dispin, dataout, dispout, code_err, disp_err);
  input [9:0]   datain;
  input  dispin;
  output [8:0] dataout;
  output dispout;
  output code_err;
  output disp_err;

  wire ai = datain[0];
  wire bi = datain[1];
  wire ci = datain[2];
  wire di = datain[3];
  wire ei = datain[4];
  wire ii = datain[5];
  wire fi = datain[6];
  wire gi = datain[7];
  wire hi = datain[8];
  wire ji = datain[9];

  wire aeqb = (ai & bi) | (!ai & !bi);
  wire ceqd = (ci & di) | (!ci & !di);
  wire p22 = (ai & bi & !ci & !di) |
      (ci & di & !ai & !bi) |
      ( !aeqb & !ceqd);
  wire p13 = ( !aeqb & !ci & !di) |
      ( !ceqd & !ai & !bi);
  wire p31 = ( !aeqb & ci & di) |
      ( !ceqd & ai & bi);

  wire p40 = ai & bi & ci & di;
  wire p04 = !ai & !bi & !ci & !di;

  wire disp6a = p31 | (p22 & dispin); // pos disp if p22 and was pos, or p31.
   wire disp6a2 = p31 & dispin;  // disp is ++ after 4 bits
   wire disp6a0 = p13 & ! dispin; // -- disp after 4 bits
    
  wire disp6b = (((ei & ii & ! disp6a0) | (disp6a & (ei | ii)) | disp6a2 |
    (ei & ii & di)) & (ei | ii | di));

  // The 5B/6B decoding special cases where ABCDE != abcde

  wire p22bceeqi = p22 & bi & ci & (ei == ii);
  wire p22bncneeqi = p22 & !bi & !ci & (ei == ii);
  wire p13in = p13 & !ii;
  wire p31i = p31 & ii;
  wire p13dei = p13 & di & ei & ii;
  wire p22aceeqi = p22 & ai & ci & (ei == ii);
  wire p22ancneeqi = p22 & !ai & !ci & (ei == ii);
  wire p13en = p13 & !ei;
  wire anbnenin = !ai & !bi & !ei & !ii;
  wire abei = ai & bi & ei & ii;
  wire cdei = ci & di & ei & ii;
  wire cndnenin = !ci & !di & !ei & !ii;

  // non-zero disparity cases:
  wire p22enin = p22 & !ei & !ii;
  wire p22ei = p22 & ei & ii;
  //wire p13in = p12 & !ii;
  //wire p31i = p31 & ii;
  wire p31dnenin = p31 & !di & !ei & !ii;
  //wire p13dei = p13 & di & ei & ii;
  wire p31e = p31 & ei;

  wire compa = p22bncneeqi | p31i | p13dei | p22ancneeqi | 
  p13en | abei | cndnenin;
  wire compb = p22bceeqi | p31i | p13dei | p22aceeqi | 
  p13en | abei | cndnenin;
  wire compc = p22bceeqi | p31i | p13dei | p22ancneeqi | 
  p13en | anbnenin | cndnenin;
  wire compd = p22bncneeqi | p31i | p13dei | p22aceeqi |
  p13en | abei | cndnenin;
  wire compe = p22bncneeqi | p13in | p13dei | p22ancneeqi | 
  p13en | anbnenin | cndnenin;

  wire ao = ai ^ compa;
  wire bo = bi ^ compb;
  wire co = ci ^ compc;
  wire do_ = di ^ compd;
  wire eo = ei ^ compe;

  wire feqg = (fi & gi) | (!fi & !gi);
  wire heqj = (hi & ji) | (!hi & !ji);
  wire fghj22 = (fi & gi & !hi & !ji) |
  (!fi & !gi & hi & ji) |
  ( !feqg & !heqj);
  wire fghjp13 = ( !feqg & !hi & !ji) |
   ( !heqj & !fi & !gi);
  wire fghjp31 = ( (!feqg) & hi & ji) |
   ( !heqj & fi & gi);

  wire dispout = (fghjp31 | (disp6b & fghj22) | (hi & ji)) & (hi | ji);

  wire ko = ( (ci & di & ei & ii) | ( !ci & !di & !ei & !ii) |
  (p13 & !ei & ii & gi & hi & ji) |
  (p31 & ei & !ii & !gi & !hi & !ji));

  wire alt7 =   (fi & !gi & !hi & // 1000 cases, where disp6b is 1
   ((dispin & ci & di & !ei & !ii) | ko |
    (dispin & !ci & di & !ei & !ii))) |
  (!fi & gi & hi & // 0111 cases, where disp6b is 0
   (( !dispin & !ci & !di & ei & ii) | ko |
    ( !dispin & ci & !di & ei & ii)));

  wire k28 = (ci & di & ei & ii) | ! (ci | di | ei | ii);
  // k28 with positive disp into fghi - .1, .2, .5, and .6 special cases
  wire k28p = ! (ci | di | ei | ii);
  wire fo = (ji & !fi & (hi | !gi | k28p)) |
     (fi & !ji & (!hi | gi | !k28p)) |
     (k28p & gi & hi) |
     (!k28p & !gi & !hi);
  wire go = (ji & !fi & (hi | !gi | !k28p)) |
     (fi & !ji & (!hi | gi |k28p)) |
     (!k28p & gi & hi) |
     (k28p & !gi & !hi);
  wire ho = ((ji ^ hi) & ! ((!fi & gi & !hi & ji & !k28p) | (!fi & gi & hi & !ji & k28p) | 
       (fi & !gi & !hi & ji & !k28p) | (fi & !gi & hi & !ji & k28p))) |
     (!fi & gi & hi & ji) | (fi & !gi & !hi & !ji);

  wire disp6p = (p31 & (ei | ii)) | (p22 & ei & ii);
  wire disp6n = (p13 & ! (ei & ii)) | (p22 & !ei & !ii);
  wire disp4p = fghjp31;
  wire disp4n = fghjp13;

  assign code_err = p40 | p04 | (fi & gi & hi & ji) | (!fi & !gi & !hi & !ji) |
      (p13 & !ei & !ii) | (p31 & ei & ii) |
      (ei & ii & fi & gi & hi) | (!ei & !ii & !fi & !gi & !hi) |
      (ei & !ii & gi & hi & ji) | (!ei & ii & !gi & !hi & !ji) |
      (!p31 & ei & !ii & !gi & !hi & !ji) |
      (!p13 & !ei & ii & gi & hi & ji) |
      (((ei & ii & !gi & !hi & !ji) |
        (!ei & !ii & gi & hi & ji)) &
       ! ((ci & di & ei) | (!ci & !di & !ei))) |
      (disp6p & disp4p) | (disp6n & disp4n) |
      (ai & bi & ci & !ei & !ii & ((!fi & !gi) | fghjp13)) |
      (!ai & !bi & !ci & ei & ii & ((fi & gi) | fghjp31)) |
      (fi & gi & !hi & !ji & disp6p) |
      (!fi & !gi & hi & ji & disp6n) |
      (ci & di & ei & ii & !fi & !gi & !hi) |
      (!ci & !di & !ei & !ii & fi & gi & hi);

  assign dataout = {ko, ho, go, fo, eo, do_, co, bo, ao};

  // my disp err fires for any legal codes that violate disparity, may fire for illegal codes
   assign disp_err = ((dispin & disp6p) | (disp6n & !dispin) |
        (dispin & !disp6n & fi & gi) |
        (dispin & ai & bi & ci) |
        (dispin & !disp6n & disp4p) |
        (!dispin & !disp6p & !fi & !gi) |
        (!dispin & !ai & !bi & !ci) |
        (!dispin & !disp6p & disp4n) |
        (disp6p & disp4p) | (disp6n & disp4n));
endmodule


module encode_8b10b (datain, dispin, dataout, dispout);
  input [8:0]   datain;
  input  dispin;  // 0 = neg disp; 1 = pos disp
  output [9:0] dataout;
  output dispout;

  wire ai = datain[0];
  wire bi = datain[1];
  wire ci = datain[2];
  wire di = datain[3];
  wire ei = datain[4];
  wire fi = datain[5];
  wire gi = datain[6];
  wire hi = datain[7];
  wire ki = datain[8];

  wire aeqb = (ai & bi) | (!ai & !bi);
  wire ceqd = (ci & di) | (!ci & !di);
  wire l22 = (ai & bi & !ci & !di) |
      (ci & di & !ai & !bi) |
      ( !aeqb & !ceqd);
  wire l40 = ai & bi & ci & di;
  wire l04 = !ai & !bi & !ci & !di;
  wire l13 = ( !aeqb & !ci & !di) |
      ( !ceqd & !ai & !bi);
  wire l31 = ( !aeqb & ci & di) |
      ( !ceqd & ai & bi);

  // The 5B/6B encoding

  wire ao = ai;
  wire bo = (bi & !l40) | l04;
  wire co = l04 | ci | (ei & di & !ci & !bi & !ai);
  wire do_ = di & ! (ai & bi & ci);
  wire eo = (ei | l13) & ! (ei & di & !ci & !bi & !ai);
  wire io = (l22 & !ei) |
     (ei & !di & !ci & !(ai&bi)) |  // D16, D17, D18
     (ei & l40) |
     (ki & ei & di & ci & !bi & !ai) | // K.28
     (ei & !di & ci & !bi & !ai);

  // pds16 indicates cases where d-1 is assumed + to get our encoded value
  wire pd1s6 = (ei & di & !ci & !bi & !ai) | (!ei & !l22 & !l31);
  // nds16 indicates cases where d-1 is assumed - to get our encoded value
  wire nd1s6 = ki | (ei & !l22 & !l13) | (!ei & !di & ci & bi & ai);

  // ndos6 is pds16 cases where d-1 is + yields - disp out - all of them
  wire ndos6 = pd1s6;
  // pdos6 is nds16 cases where d-1 is - yields + disp out - all but one
  wire pdos6 = ki | (ei & !l22 & !l13);


  // some Dx.7 and all Kx.7 cases result in run length of 5 case unless
  // an alternate coding is used (referred to as Dx.A7, normal is Dx.P7)
  // specifically, D11, D13, D14, D17, D18, D19.
  wire alt7 = fi & gi & hi & (ki | 
         (dispin ? (!ei & di & l31) : (ei & !di & l13)));

   
  wire fo = fi & ! alt7;
  wire go = gi | (!fi & !gi & !hi);
  wire ho = hi;
  wire jo = (!hi & (gi ^ fi)) | alt7;

  // nd1s4 is cases where d-1 is assumed - to get our encoded value
  wire nd1s4 = fi & gi;
  // pd1s4 is cases where d-1 is assumed + to get our encoded value
  wire pd1s4 = (!fi & !gi) | (ki & ((fi & !gi) | (!fi & gi)));

  // ndos4 is pd1s4 cases where d-1 is + yields - disp out - just some
  wire ndos4 = (!fi & !gi);
  // pdos4 is nd1s4 cases where d-1 is - yields + disp out 
  wire pdos4 = fi & gi & hi;

  // only legal K codes are K28.0->.7, K23/27/29/30.7
  // K28.0->7 is ei=di=ci=1,bi=ai=0
  // K23 is 10111
  // K27 is 11011
  // K29 is 11101
  // K30 is 11110 - so K23/27/29/30 are ei & l31
  wire illegalk = ki & 
    (ai | bi | !ci | !di | !ei) & // not K28.0->7
    (!fi | !gi | !hi | !ei | !l31); // not K23/27/29/30.7

  // now determine whether to do the complementing
  // complement if prev disp is - and pd1s6 is set, or + and nd1s6 is set
  wire compls6 = (pd1s6 & !dispin) | (nd1s6 & dispin);

  // disparity out of 5b6b is disp in with pdso6 and ndso6
  // pds16 indicates cases where d-1 is assumed + to get our encoded value
  // ndos6 is cases where d-1 is + yields - disp out
  // nds16 indicates cases where d-1 is assumed - to get our encoded value
  // pdos6 is cases where d-1 is - yields + disp out
  // disp toggles in all ndis16 cases, and all but that 1 nds16 case

  wire disp6 = dispin ^ (ndos6 | pdos6);

  wire compls4 = (pd1s4 & !disp6) | (nd1s4 & disp6);
  assign dispout = disp6 ^ (ndos4 | pdos4);

  assign dataout = {(jo ^ compls4), (ho ^ compls4),
      (go ^ compls4), (fo ^ compls4),
      (io ^ compls6), (eo ^ compls6),
      (do_ ^ compls6), (co ^ compls6),
      (bo ^ compls6), (ao ^ compls6)};
endmodule