Version abc80228

4 files changed, 1112 insertions, 195 deletions

diff --git a/src/opt/fret/fretFlow.c b/src/opt/fret/fretFlow.c
index a9cef327..4b2bd936 100644
--- a/src/opt/fret/fretFlow.c
+++ b/src/opt/fret/fretFlow.c
@@ -73,6 +73,7 @@ void dfsfast_preorder( Abc_Ntk_t *pNtk ) {
 #endif
 
   // clear histogram
+  assert(pManMR->vSinkDistHist);
   memset(Vec_IntArray(pManMR->vSinkDistHist), 0, sizeof(int)*Vec_IntSize(pManMR->vSinkDistHist));
 
   // seed queue : latches, PIOs, and blocks
diff --git a/src/opt/fret/fretInit.c b/src/opt/fret/fretInit.c
index 53df7386..47d338cb 100644
--- a/src/opt/fret/fretInit.c
+++ b/src/opt/fret/fretInit.c
@@ -23,6 +23,10 @@
 #include "io.h"
 #include "fretime.h"
 #include "mio.h"
+#include "hop.h"
+
+#undef DEBUG_PRINT_INIT_NTK
+
 
 ////////////////////////////////////////////////////////////////////////
 ///                     FUNCTION PROTOTYPES                          ///
@@ -31,20 +35,24 @@
 static void Abc_FlowRetime_UpdateForwardInit_rec( Abc_Obj_t * pObj );
 static void Abc_FlowRetime_VerifyBackwardInit( Abc_Ntk_t * pNtk );
 static void Abc_FlowRetime_VerifyBackwardInit_rec( Abc_Obj_t * pObj );
-static Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj, 
-                                                         Abc_Obj_t *pUseThisPi, Vec_Ptr_t *vOtherPis, 
-                                                         int recurse);
+static Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj );
+
 static void Abc_FlowRetime_SimulateNode( Abc_Obj_t * pObj );
 static void Abc_FlowRetime_SimulateSop( Abc_Obj_t * pObj, char *pSop );
 
-extern void * Abc_FrameReadLibGen();                    
-extern Abc_Ntk_t * Abc_NtkRestrash( Abc_Ntk_t * pNtk, bool fCleanup );
+static void Abc_FlowRetime_SetInitToOrig( Abc_Obj_t *pInit, Abc_Obj_t *pOrig );
+static void Abc_FlowRetime_GetInitToOrig( Abc_Obj_t *pInit, Abc_Obj_t **pOrig, int *lag );
+static void Abc_FlowRetime_ClearInitToOrig( Abc_Obj_t *pInit );
 
+extern void * Abc_FrameReadLibGen();
+
+extern void Abc_NtkMarkCone_rec( Abc_Obj_t * pObj, int fForward );
 
 ////////////////////////////////////////////////////////////////////////
 ///                     FUNCTION DEFINITIONS                         ///
 ////////////////////////////////////////////////////////////////////////
 
+
 /**Function*************************************************************
 
   Synopsis    [Updates initial state information.]
@@ -69,6 +77,40 @@ Abc_FlowRetime_InitState( Abc_Ntk_t * pNtk ) {
   }
 }
 
+/**Function*************************************************************
+
+  Synopsis    [Prints initial state information.]
+
+  Description [Prints distribution of 0,1,and X initial states.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+inline int
+Abc_FlowRetime_ObjFirstNonLatchBox( Abc_Obj_t * pOrigObj, Abc_Obj_t ** pResult ) {
+  int lag = 0;
+  Abc_Ntk_t *pNtk;
+  *pResult = pOrigObj;
+  pNtk = Abc_ObjNtk( pOrigObj );
+
+  Abc_NtkIncrementTravId( pNtk );
+
+  while( Abc_ObjIsBo(*pResult) || Abc_ObjIsLatch(*pResult) || Abc_ObjIsBi(*pResult) ) {
+    assert(Abc_ObjFaninNum(*pResult));
+    *pResult = Abc_ObjFanin0(*pResult);
+    
+    if (Abc_NodeIsTravIdCurrent(*pResult))
+      return -1;
+    Abc_NodeSetTravIdCurrent(*pResult);
+
+    if (Abc_ObjIsLatch(*pResult)) ++lag;
+  }
+
+  return lag;
+}
+
 
 /**Function*************************************************************
 
@@ -152,6 +194,58 @@ void Abc_FlowRetime_UpdateForwardInit_rec( Abc_Obj_t * pObj ) {
   Abc_FlowRetime_SimulateNode( pObj );
 }
 
+/**Function*************************************************************
+
+  Synopsis    [Recursively evaluates HOP netlist.]
+
+  Description [Exponential.  There aren't enough flags on a HOP node.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+static void Abc_FlowRetime_EvalHop_rec( Hop_Man_t *pHop, Hop_Obj_t *pObj, int *f, int *dc ) {
+  int f1, dc1, f2, dc2;
+  Hop_Obj_t *pReg = Hop_Regular(pObj);
+  
+  // const 0
+  if (Hop_ObjIsConst1(pReg)) {
+    *f  = 1;
+    *f ^= (pReg == pObj ? 1 : 0);
+    *dc = 0;
+    return;
+  }
+
+  // PI
+  if (Hop_ObjIsPi(pReg)) {
+    *f  = pReg->fMarkA;
+    *f ^= (pReg == pObj ? 1 : 0);
+    *dc = pReg->fMarkB;
+    return;
+  }
+
+  // PO
+  if (Hop_ObjIsPo(pReg)) {
+    assert( pReg == pObj );
+    Abc_FlowRetime_EvalHop_rec(pHop, Hop_ObjChild0(pReg), f, dc);
+    return;
+  }
+
+  // AND
+  if (Hop_ObjIsAnd(pReg)) {
+    Abc_FlowRetime_EvalHop_rec(pHop, Hop_ObjChild0(pReg), &f1, &dc1);
+    Abc_FlowRetime_EvalHop_rec(pHop, Hop_ObjChild1(pReg), &f2, &dc2);
+
+    *dc = (dc1 & f2) | (dc2 & f1) | (dc1 & dc2);
+    *f  = f1 & f2;
+    *f ^= (pReg == pObj ? 1 : 0);
+    return;
+  }
+
+  assert(0);
+}
+
 
 /**Function*************************************************************
 
@@ -196,11 +290,13 @@ void Abc_FlowRetime_SimulateNode( Abc_Obj_t * pObj ) {
   int i, rAnd, rVar, dcAnd, dcVar;
   DdManager * dd = pNtk->pManFunc;
   DdNode *pBdd = pObj->pData, *pVar;
+  Hop_Man_t *pHop = pNtk->pManFunc;
   
   assert(!Abc_ObjIsLatch(pObj));
+  assert(Abc_ObjRegular(pObj));
 
   // (i) constant nodes
-  if (Abc_NtkHasAig(pNtk) && Abc_AigNodeIsConst(pObj)) {
+  if (Abc_NtkIsStrash(pNtk) && Abc_AigNodeIsConst(pObj)) {
     Abc_FlowRetime_SetInitValue(pObj, 1, 0);
     return;
   }
@@ -258,10 +354,37 @@ void Abc_FlowRetime_SimulateNode( Abc_Obj_t * pObj ) {
     return;
   }
 
-  // ------ AIG network
-  else if ( Abc_NtkHasAig( pNtk )) {
 
-    assert(Abc_AigNodeIsAnd(pObj));
+  // ------ AIG logic network
+  else if ( Abc_NtkHasAig( pNtk ) && !Abc_NtkIsStrash( pNtk )) {
+    
+    assert(Abc_ObjIsNode(pObj));
+    assert(pObj->pData);
+    assert(Abc_ObjFaninNum(pObj) <= Hop_ManPiNum(pHop) );
+    
+    // set vals at inputs
+    Abc_ObjForEachFanin(pObj, pFanin, i) {
+      Hop_ManPi(pHop, i)->fMarkA = FTEST(pFanin, INIT_1)?1:0;
+      Hop_ManPi(pHop, i)->fMarkB = FTEST(pFanin, INIT_CARE)?1:0;
+    }
+
+    Abc_FlowRetime_EvalHop_rec( pHop, pObj->pData, &rVar, &dcVar );
+   
+    Abc_FlowRetime_SetInitValue(pObj, rVar, dcVar);
+
+    // clear flags
+    Abc_ObjForEachFanin(pObj, pFanin, i) {
+      Hop_ManPi(pHop, i)->fMarkA = 0;
+      Hop_ManPi(pHop, i)->fMarkB = 0;
+    }
+
+    return;
+  }
+
+  // ------ strashed network
+  else if ( Abc_NtkIsStrash( pNtk )) {
+
+    assert(Abc_ObjType(pObj) == ABC_OBJ_NODE);
     dcAnd = 0, rAnd = 1;
     
     pFanin = Abc_ObjFanin0(pObj);
@@ -361,7 +484,9 @@ void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk ) {
   Vec_Ptr_t *vObj = Vec_PtrAlloc(100);
 
   // create the network used for the initial state computation
-  if (Abc_NtkHasMapping(pNtk))
+  if (Abc_NtkIsStrash(pNtk)) {
+    pManMR->pInitNtk = Abc_NtkAlloc( ABC_NTK_LOGIC, ABC_FUNC_SOP, 1 );
+  } else if (Abc_NtkHasMapping(pNtk))
     pManMR->pInitNtk = Abc_NtkAlloc( pNtk->ntkType, ABC_FUNC_SOP, 1 );
   else
     pManMR->pInitNtk = Abc_NtkAlloc( pNtk->ntkType, pNtk->ntkFunc, 1 );
@@ -371,14 +496,12 @@ void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk ) {
     // map latch to initial state network
     pPi = Abc_NtkCreatePi( pManMR->pInitNtk );
 
+    // DEBUG
+    // printf("setup : mapping latch %d to PI %d\n", pLatch->Id, pPi->Id);
+
     // has initial state requirement?
     if (Abc_LatchIsInit0(pLatch)) {
-      
-      if (Abc_NtkHasAig(pNtk))
-        pObj = Abc_ObjNot( pPi );
-      else
-        pObj = Abc_NtkCreateNodeInv( pManMR->pInitNtk, pPi );
-
+      pObj = Abc_NtkCreateNodeInv( pManMR->pInitNtk, pPi );
       Vec_PtrPush(vObj, pObj);
     }
     else if (Abc_LatchIsInit1(pLatch)) {
@@ -397,14 +520,9 @@ void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk ) {
     pManMR->fSolutionIsDc = 0;
 
   // mitre output
-  if (Abc_NtkHasAig(pNtk)) {
-    // create AND-by-AND
-    pObj = Vec_PtrPop( vObj );
-    while( Vec_PtrSize(vObj) )
-      pObj = Abc_AigAnd( pManMR->pInitNtk->pManFunc, pObj, Vec_PtrPop( vObj ) ); 
-  } else
-    // create n-input AND gate
-    pObj = Abc_NtkCreateNodeAnd( pManMR->pInitNtk, vObj );
+
+  // create n-input AND gate
+  pObj = Abc_NtkCreateNodeAnd( pManMR->pInitNtk, vObj );
 
   Abc_ObjAddFanin( Abc_NtkCreatePo( pManMR->pInitNtk ), pObj );
 
@@ -418,7 +536,7 @@ void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk ) {
 
   Description []
                
-  SideEffects []
+  SideEffects [Sets object copies in init ntk.]
 
   SeeAlso     []
 
@@ -427,13 +545,13 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
   int i;
   Abc_Obj_t *pObj, *pInitObj;
   Vec_Ptr_t *vDelete = Vec_PtrAlloc(0);
+  Abc_Ntk_t *pSatNtk;
   int result;
 
   assert(pManMR->pInitNtk);
 
   // is the solution entirely DC's?
   if (pManMR->fSolutionIsDc) {
-    Abc_NtkDelete(pManMR->pInitNtk);
     Vec_PtrFree(vDelete);
     Abc_NtkForEachLatch( pNtk, pObj, i ) Abc_LatchSetInitDc( pObj );
     vprintf("\tno init state computation: all-don't-care solution\n");
@@ -441,15 +559,10 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
   }
 
   // check that network is combinational
-  // mark superfluous BI nodes for deletion
   Abc_NtkForEachObj( pManMR->pInitNtk, pObj, i ) {
     assert(!Abc_ObjIsLatch(pObj));
     assert(!Abc_ObjIsBo(pObj));
-    
-    if (Abc_ObjIsBi(pObj)) {
-      Abc_ObjBetterTransferFanout( pObj, Abc_ObjFanin0(pObj), Abc_ObjFaninC0(pObj) );
-      Vec_PtrPush( vDelete, pObj );
-    }
+    assert(!Abc_ObjIsBi(pObj));
   }
   
   // delete superfluous nodes
@@ -464,9 +577,13 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
   Abc_NtkAddDummyPiNames(pManMR->pInitNtk);
   if (Abc_NtkIsLogic(pManMR->pInitNtk))
     Abc_NtkCleanup(pManMR->pInitNtk, 0);
-  else if (Abc_NtkIsStrash(pManMR->pInitNtk)) {  
-    Abc_NtkReassignIds(pManMR->pInitNtk);
-  }
+
+#if defined(DEBUG_PRINT_INIT_NTK)
+  Abc_NtkLevelReverse( pManMR->pInitNtk );
+  Abc_NtkForEachObj( pManMR->pInitNtk, pObj, i ) 
+    if (Abc_ObjLevel( pObj ) < 2)
+      Abc_ObjPrint(stdout, pObj);
+#endif
   
   vprintf("\tsolving for init state (%d nodes)... ", Abc_NtkObjNum(pManMR->pInitNtk));
   fflush(stdout);
@@ -474,17 +591,19 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
   // convert SOPs to BDD
   if (Abc_NtkHasSop(pManMR->pInitNtk))
     Abc_NtkSopToBdd( pManMR->pInitNtk );
+  // convert AIGs to BDD
+  if (Abc_NtkHasAig(pManMR->pInitNtk))
+    Abc_NtkAigToBdd( pManMR->pInitNtk );  
+
+  pSatNtk = pManMR->pInitNtk;
   
   // solve
-  result = Abc_NtkMiterSat( pManMR->pInitNtk, (sint64)500000, (sint64)50000000, 0, NULL, NULL );
+  result = Abc_NtkMiterSat( pSatNtk, (sint64)500000, (sint64)50000000, 0, NULL, NULL );
 
   if (!result) { 
     vprintf("SUCCESS\n");
   } else  {    
     vprintf("FAILURE\n");
-    printf("WARNING: no equivalent init state. setting all initial states to don't-cares\n");
-    Abc_NtkForEachLatch( pNtk, pObj, i ) Abc_LatchSetInitDc( pObj );
-    Abc_NtkDelete(pManMR->pInitNtk);
     return 0;
   }
 
@@ -495,6 +614,9 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
     assert( Abc_ObjIsPi( pInitObj ));
     Abc_ObjSetCopy( pInitObj, pObj );
     Abc_LatchSetInitNone( pObj );
+
+    // DEBUG
+    // printf("solve : getting latch %d from PI %d\n", pObj->Id, pInitObj->Id);
   }
 
   // copy solution from PIs to latches
@@ -513,9 +635,6 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
   Abc_NtkForEachLatch( pNtk, pObj, i ) assert( !Abc_LatchIsInitNone( pObj ) );
 #endif
 
-  // deallocate
-  Abc_NtkDelete( pManMR->pInitNtk );
-
   return 1;
 }
 
@@ -534,7 +653,9 @@ int Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
 void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk ) {
   Abc_Obj_t *pOrigObj,  *pInitObj;
   Vec_Ptr_t *vBo = Vec_PtrAlloc(100);
-  Vec_Ptr_t *vOldPis = Vec_PtrAlloc(100);
+  Vec_Ptr_t *vPi = Vec_PtrAlloc(100);
+  Abc_Ntk_t *pInitNtk = pManMR-> pInitNtk;
+  Abc_Obj_t *pBuf;
   int i;
 
   // remove PIs from network (from BOs)
@@ -542,18 +663,43 @@ void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk ) {
     if (Abc_ObjIsBo(pOrigObj)) {
       pInitObj = FDATA(pOrigObj)->pInitObj;
       assert(Abc_ObjIsPi(pInitObj));
-      Vec_PtrPush(vBo, pOrigObj);
 
-      Abc_FlowRetime_UpdateBackwardInit_rec( Abc_ObjFanin0( pOrigObj ), pInitObj, vOldPis, 0 );
-    }
+      // DEBUG
+      // printf("update : freeing PI %d\n", pInitObj->Id);
+      
+      // create a buffer instead
+      pBuf = Abc_NtkCreateNodeBuf( pInitNtk, NULL );
+      Abc_FlowRetime_ClearInitToOrig( pBuf );
 
-  // add PIs to network (at latches)
-  Abc_NtkForEachLatch( pNtk, pOrigObj, i )
-    Abc_FlowRetime_UpdateBackwardInit_rec( pOrigObj, NULL, vOldPis, 0 );
+      Abc_ObjBetterTransferFanout( pInitObj, pBuf, 0 );
+      FDATA(pOrigObj)->pInitObj = pBuf;
+      pOrigObj->fMarkA = 1;
+
+      Vec_PtrPush(vBo, pOrigObj);
+      Vec_PtrPush(vPi, pInitObj);
+    }
   
-  // connect nodes in init state network
+  // check that PIs are all free
+  Abc_NtkForEachPi( pInitNtk, pInitObj, i) {
+    assert( Abc_ObjFanoutNum( pInitObj ) == 0);
+  }
+
+  // add PIs to to latches
+  Abc_NtkForEachLatch( pNtk, pOrigObj, i ) {
+    assert(Vec_PtrSize(vPi) > 0);
+    pInitObj = Vec_PtrPop(vPi);
+
+    // DEBUG
+    // printf("update : mapping latch %d to PI %d\n", pOrigObj->Id, pInitObj->Id);
+
+    pOrigObj->fMarkA = pOrigObj->fMarkB = 1;
+    FDATA(pOrigObj)->pInitObj = pInitObj;
+    Abc_ObjSetData(pOrigObj, pInitObj);
+  }  
+
+  // recursively build init network
   Vec_PtrForEachEntry( vBo, pOrigObj, i )
-    Abc_FlowRetime_UpdateBackwardInit_rec( Abc_ObjFanin0( pOrigObj ), NULL, NULL, 1 );
+    Abc_FlowRetime_UpdateBackwardInit_rec( pOrigObj );
   
   // clear flags
   Abc_NtkForEachObj( pNtk, pOrigObj, i )
@@ -561,12 +707,95 @@ void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk ) {
 
   // deallocate
   Vec_PtrFree( vBo );
-  Vec_PtrFree( vOldPis );
+  Vec_PtrFree( vPi );
 }
 
 
 /**Function*************************************************************
 
+  Synopsis    [Creates a corresponding node in the init state network]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+Abc_Obj_t *Abc_FlowRetime_CopyNodeToInitNtk( Abc_Obj_t *pOrigObj ) {
+  Abc_Ntk_t *pNtk = pManMR->pNtk;
+  Abc_Ntk_t *pInitNtk = pManMR->pInitNtk;
+  Abc_Obj_t *pInitObj;
+  void *pData;
+  int fCompl[2];
+
+  assert(pOrigObj);
+
+  // what we do depends on the ntk types of original / init networks...
+  
+  // (0) convert BI/BO nodes to buffers
+  if (Abc_ObjIsBi( pOrigObj ) || Abc_ObjIsBo( pOrigObj ) ) {
+    pInitObj =  Abc_NtkCreateNodeBuf( pInitNtk, NULL );
+    Abc_FlowRetime_ClearInitToOrig( pInitObj );
+    return pInitObj;
+  }
+
+  // (i) strash node -> SOP node
+  if (Abc_NtkIsStrash( pNtk )) {
+
+    if (Abc_AigNodeIsConst( pOrigObj )) {
+      return Abc_NtkCreateNodeConst1( pInitNtk );
+    }
+    if (!Abc_ObjIsNode( pOrigObj )) {
+      assert(Abc_ObjFaninNum(pOrigObj) == 1);
+      pInitObj =  Abc_NtkCreateNodeBuf( pInitNtk, NULL );
+      Abc_FlowRetime_ClearInitToOrig( pInitObj );
+      return pInitObj;
+    }
+
+    assert( Abc_ObjIsNode(pOrigObj) );
+    pInitObj = Abc_NtkCreateObj( pInitNtk, ABC_OBJ_NODE );
+    
+    fCompl[0] = pOrigObj->fCompl0 ? 1 : 0;
+    fCompl[1] = pOrigObj->fCompl1 ? 1 : 0;
+    
+    pData =  Abc_SopCreateAnd( pInitNtk->pManFunc, 2, fCompl );
+    assert(pData);
+    pInitObj->pData = Abc_SopRegister( pInitNtk->pManFunc, pData );
+  } 
+
+  // (ii) mapped node -> SOP node
+  else if (Abc_NtkHasMapping( pNtk )) {
+    if (!pOrigObj->pData) {
+      // assume terminal...
+      assert(Abc_ObjFaninNum(pOrigObj) == 1);
+
+      pInitObj =  Abc_NtkCreateNodeBuf( pInitNtk, NULL );
+      Abc_FlowRetime_ClearInitToOrig( pInitObj );
+      return pInitObj;
+    }
+
+    pInitObj = Abc_NtkCreateObj( pInitNtk, Abc_ObjType(pOrigObj) );
+    pData = Mio_GateReadSop(pOrigObj->pData);
+    assert( Abc_SopGetVarNum(pData) == Abc_ObjFaninNum(pOrigObj) );
+    
+    pInitObj->pData = Abc_SopRegister( pInitNtk->pManFunc, pData );
+  } 
+
+  // (iii) otherwise, duplicate obj
+  else {
+    pInitObj = Abc_NtkDupObj( pInitNtk, pOrigObj, 0 );
+    
+    // copy phase
+    pInitObj->fPhase = pOrigObj->fPhase;
+  }
+
+  assert(pInitObj);
+  return pInitObj;
+}
+
+/**Function*************************************************************
+
   Synopsis    [Updates backward initial state computation problem.]
 
   Description [Creates a duplicate node in the initial state network 
@@ -587,87 +816,43 @@ void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk ) {
   SeeAlso     []
 
 ***********************************************************************/
-Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj, 
-                                                  Abc_Obj_t *pUseThisPi, Vec_Ptr_t *vOtherPis, 
-                                                  int fRecurse) {
-  Abc_Obj_t *pInitObj, *pOrigFanin, *pInitFanin;
-  void      *pData;
+Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj) {
+  Abc_Obj_t *pOrigFanin, *pInitFanin, *pInitObj;
   int i;
-  Abc_Ntk_t *pNtk = Abc_ObjNtk( pOrigObj );
+
+  assert(pOrigObj);
 
   // should never reach primary IOs
   assert(!Abc_ObjIsPi(pOrigObj));
   assert(!Abc_ObjIsPo(pOrigObj));
 
-  // if fanin is latch, it becomes a primary input
-  if (Abc_ObjIsLatch( pOrigObj )) {
-    if (pOrigObj->fMarkA)  return FDATA(pOrigObj)->pInitObj;
-
-    assert(vOtherPis);
-    
-    if (pUseThisPi) { 
-      // reuse curent PI     
-      pInitObj = pUseThisPi; }
-    else { 
-      // reuse previous PI
-      pInitObj = (Abc_Obj_t*)Vec_PtrPop(vOtherPis); 
-    }
-    
-    // remember link from original node to init ntk
-    Abc_ObjSetData( pOrigObj, pInitObj ); 
-
-    pOrigObj->fMarkA = 1;
-    return (FDATA(pOrigObj)->pInitObj = pInitObj);
-  } 
+  // skip bias nodes
+  if (FTEST(pOrigObj, BIAS_NODE)) 
+    return NULL;
 
   // does an init node already exist?
   if(!pOrigObj->fMarkA) {
 
-    if (Abc_NtkHasMapping( pNtk )) {
-      if (!pOrigObj->pData) {
-        // assume terminal...
-        assert(Abc_ObjFaninNum(pOrigObj) == 1);
-        pInitObj = Abc_NtkCreateNodeBuf( pManMR->pInitNtk, NULL );
-      } else {
-        pInitObj = Abc_NtkCreateObj( pManMR->pInitNtk, Abc_ObjType(pOrigObj) );
-        pData = Mio_GateReadSop(pOrigObj->pData);
-        assert( Abc_SopGetVarNum(pData) == Abc_ObjFaninNum(pOrigObj) );
-
-        pInitObj->pData = Abc_SopRegister( pManMR->pInitNtk->pManFunc, pData );
-      }
-    } else {
-      pData = Abc_ObjCopy( pOrigObj );   // save ptr to flow data    
-      if (Abc_NtkIsStrash( pNtk ) && Abc_AigNodeIsConst( pOrigObj ))
-        pInitObj = Abc_AigConst1( pManMR->pInitNtk );
-      else
-        pInitObj = Abc_NtkDupObj( pManMR->pInitNtk, pOrigObj, 0 );
-      Abc_ObjSetCopy( pOrigObj, pData ); // restore ptr to flow data
-
-      // copy complementation
-      pInitObj->fCompl0 = pOrigObj->fCompl0;
-      pInitObj->fCompl1 = pOrigObj->fCompl1;
-      pInitObj->fPhase = pOrigObj->fPhase;
-    }
+    pInitObj = Abc_FlowRetime_CopyNodeToInitNtk( pOrigObj );
 
-    // if we didn't use given PI, immediately transfer fanouts
-    // and add to list for later reuse
-    if (pUseThisPi) {
-      Abc_ObjBetterTransferFanout( pUseThisPi, pInitObj, 0 );
-      Vec_PtrPush( vOtherPis, pUseThisPi );
-    }
+    Abc_FlowRetime_SetInitToOrig( pInitObj, pOrigObj );
+    FDATA(pOrigObj)->pInitObj = pInitObj;
 
     pOrigObj->fMarkA = 1;
-    FDATA(pOrigObj)->pInitObj = pInitObj;
   } else {
     pInitObj = FDATA(pOrigObj)->pInitObj;
   }
+  assert(pInitObj);
     
   // have we already connected this object?
-  if (fRecurse && !pOrigObj->fMarkB) {
+  if (!pOrigObj->fMarkB) {
 
     // create and/or connect fanins
     Abc_ObjForEachFanin( pOrigObj, pOrigFanin, i ) {
-      pInitFanin = Abc_FlowRetime_UpdateBackwardInit_rec( pOrigFanin, NULL, NULL, fRecurse );
+      // should not reach BOs (i.e. the start of the next frame)
+      // the new latch bounday should lie before it
+      assert(!Abc_ObjIsBo( pOrigFanin ));
+      pInitFanin = Abc_FlowRetime_UpdateBackwardInit_rec( pOrigFanin );
       Abc_ObjAddFanin( pInitObj, pInitFanin );
     }
 
@@ -745,6 +930,72 @@ void Abc_FlowRetime_VerifyBackwardInit_rec( Abc_Obj_t * pObj ) {
   Abc_FlowRetime_SimulateNode( pObj );
 }
 
+/**Function*************************************************************
+
+  Synopsis    [Constrains backward retiming for initializability.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+bool Abc_FlowRetime_PartialSat(Vec_Ptr_t *vNodes, int cut) {
+  Abc_Ntk_t *pPartNtk, *pInitNtk = pManMR->pInitNtk;
+  Abc_Obj_t *pObj, *pNext, *pPartObj, *pPartNext, *pPo;
+  int i, j, result;
+
+  assert( Abc_NtkPoNum( pInitNtk ) == 1 );
+
+  pPartNtk = Abc_NtkAlloc( pInitNtk->ntkType, pInitNtk->ntkFunc, 0 );
+
+  // copy network
+  Vec_PtrForEachEntry( vNodes, pObj, i ) {
+    pObj->Level = i;
+    assert(!Abc_ObjIsPo( pObj ));
+
+    if (i < cut && !pObj->fMarkA) {
+      pPartObj = Abc_NtkCreatePi( pPartNtk );
+      Abc_ObjSetCopy( pObj, pPartObj );
+    } else {
+      // copy node
+      pPartObj = Abc_NtkDupObj( pPartNtk, pObj, 0 );
+      // copy complementation
+      pPartObj->fPhase = pObj->fPhase;
+   
+      // connect fanins
+      Abc_ObjForEachFanin( pObj, pNext, j ) {   
+        pPartNext = Abc_ObjCopy( pNext );
+        assert(pPartNext);
+        Abc_ObjAddFanin( pPartObj, pPartNext );
+      }
+    }
+
+    assert(pObj->pCopy == pPartObj);
+  }
+  
+  // create PO
+  pPo = Abc_NtkCreatePo( pPartNtk );
+  pNext = Abc_ObjFanin0( Abc_NtkPo( pInitNtk, 0 ) );
+  pPartNext = Abc_ObjCopy( pNext );
+  assert( pPartNext );
+  Abc_ObjAddFanin( pPo, pPartNext );
+  
+  // check network
+#if defined(DEBUG_CHECK)
+  Abc_NtkAddDummyPoNames(pPartNtk);
+  Abc_NtkAddDummyPiNames(pPartNtk);
+  Abc_NtkCheck( pPartNtk );
+#endif
+
+  result = Abc_NtkMiterSat( pPartNtk, (sint64)500000, (sint64)50000000, 0, NULL, NULL );
+
+  Abc_NtkDelete( pPartNtk );
+ 
+  return !result;
+}
+
 
 /**Function*************************************************************
 
@@ -758,5 +1009,321 @@ void Abc_FlowRetime_VerifyBackwardInit_rec( Abc_Obj_t * pObj ) {
 
 ***********************************************************************/
 void Abc_FlowRetime_ConstrainInit( ) {
-  // unimplemented
+  Vec_Ptr_t *vNodes;
+  int low, high, mid;
+  int i, n, lag;
+  Abc_Obj_t *pObj = NULL, *pOrigObj;
+  InitConstraint_t *pConstraint = ALLOC( InitConstraint_t, 1 );
+
+  memset( pConstraint, 0, sizeof(InitConstraint_t) );
+
+  assert(pManMR->pInitNtk);
+
+  vprintf("\tsearch for initial state conflict...\n");
+
+  vNodes = Abc_NtkDfs(pManMR->pInitNtk, 0);
+  n = Vec_PtrSize(vNodes);
+  // also add PIs to vNodes
+  Abc_NtkForEachPi(pManMR->pInitNtk, pObj, i) 
+    Vec_PtrPush(vNodes, pObj);
+  Vec_PtrReorder(vNodes, n);
+
+#if defined(DEBUG_CHECK)
+    assert(!Abc_FlowRetime_PartialSat( vNodes, 0 ));
+#endif
+
+  // grow initialization constraint
+  do {
+    vprintf("\t\t");
+
+    // find element to add to set...
+    low = 0, high = Vec_PtrSize(vNodes);
+    while (low != high-1) {
+      mid = (low + high) >> 1;
+      
+      if (!Abc_FlowRetime_PartialSat( vNodes, mid )) {
+        low = mid;
+        vprintf("-");
+      } else {
+        high = mid;
+        vprintf("*");
+      }
+      fflush(stdout);
+    }
+      
+#if defined(DEBUG_CHECK)
+    assert(Abc_FlowRetime_PartialSat( vNodes, high ));
+    assert(!Abc_FlowRetime_PartialSat( vNodes, low ));
+#endif
+    
+    // mark its TFO
+    pObj = Vec_PtrEntry( vNodes, low );
+    Abc_NtkMarkCone_rec( pObj, 1 );
+    vprintf("   conflict term = %d ", low);
+
+#if 0
+    printf("init ------\n");
+    Abc_ObjPrint(stdout, pObj);
+    printf("\n");
+    Abc_ObjPrintNeighborhood( pObj, 1 );
+    printf("------\n");
+#endif
+
+    // add node to constraint
+    Abc_FlowRetime_GetInitToOrig( pObj, &pOrigObj, &lag );
+    assert(pOrigObj);
+    vprintf(" <=> %d/%d\n", Abc_ObjId(pOrigObj), lag);
+
+#if 0    
+    printf("orig ------\n");
+    Abc_ObjPrint(stdout, pOrigObj);
+    printf("\n");
+    Abc_ObjPrintNeighborhood( pOrigObj, 1 );
+    printf("------\n");
+#endif
+    Vec_IntPush( &pConstraint->vNodes, Abc_ObjId(pOrigObj) );
+    Vec_IntPush( &pConstraint->vLags, lag );
+
+  } while (Abc_FlowRetime_PartialSat( vNodes, Vec_PtrSize(vNodes) ));
+
+  pConstraint->pBiasNode = NULL;
+
+  // add constraint
+  Vec_PtrPush( pManMR->vInitConstraints, pConstraint );
+
+  // clear marks
+  Abc_NtkForEachObj( pManMR->pInitNtk, pObj, i)
+    pObj->fMarkA = 0;
+
+  // free
+  Vec_PtrFree( vNodes );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Removes nodes to bias against uninitializable cuts.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_RemoveInitBias( ) {
+  // Abc_Ntk_t *pNtk = pManMR->pNtk;
+  Abc_Obj_t *pBiasNode;
+  InitConstraint_t *pConstraint;
+  int i;
+
+  Vec_PtrForEachEntry( pManMR->vInitConstraints, pConstraint, i ) {
+    pBiasNode = pConstraint->pBiasNode;
+    pConstraint->pBiasNode = NULL;
+
+    if (pBiasNode)
+      Abc_NtkDeleteObj(pBiasNode);
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Connects the bias node to one of the constraint vertices.]
+
+  Description [ACK!
+               Currently this is dumb dumb hack.
+               What should we do with biases that belong on BOs?  These
+               move through the circuit.
+               Currently, the bias gets marked on the fan-in of BO
+               and the bias gets implemented on every BO fan-out of a
+               node.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+static void Abc_FlowRetime_ConnectBiasNode(Abc_Obj_t *pBiasNode, Abc_Obj_t *pObj, int biasLag) {
+  Abc_Obj_t *pCur, *pNext;
+  int i;
+  int lag;
+  Vec_Ptr_t *vNodes = Vec_PtrAlloc(1);
+  Vec_Int_t *vLags = Vec_IntAlloc(1);
+  Abc_Ntk_t *pNtk = Abc_ObjNtk( pObj );
+  
+  Vec_PtrPush( vNodes, pObj );
+  Vec_IntPush( vLags, 0 );
+
+  Abc_NtkIncrementTravId( pNtk );
+
+  while (Vec_PtrSize( vNodes )) {
+    pCur = Vec_PtrPop( vNodes );
+    lag = Vec_IntPop( vLags );
+
+    if (Abc_NodeIsTravIdCurrent( pCur )) continue;
+    Abc_NodeSetTravIdCurrent( pCur );
+
+    if (!Abc_ObjIsLatch(pCur) &&
+        !Abc_ObjIsBo(pCur) &&
+        Abc_FlowRetime_GetLag(pObj)+lag == biasLag ) {
+
+      // printf("biasing : ");
+      // Abc_ObjPrint(stdout,  pCur );
+#if 1
+      FSET( pCur, BLOCK );
+#else
+      Abc_ObjAddFanin( pCur, pBiasNode );
+#endif
+    }
+
+    Abc_ObjForEachFanout( pCur, pNext, i ) {
+      if (Abc_ObjIsBi(pNext) ||
+          Abc_ObjIsLatch(pNext) ||
+          Abc_ObjIsBo(pNext) ||
+          Abc_ObjIsBo(pCur)) {
+        Vec_PtrPush( vNodes, pNext );
+        Vec_IntPush( vLags, lag - Abc_ObjIsLatch(pNext) ? 1 : 0 );
+      }
+    }
+  }
+
+  Vec_PtrFree( vNodes );
+  Vec_IntFree( vLags );
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Adds nodes to bias against uninitializable cuts.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_AddInitBias( ) {
+  Abc_Ntk_t *pNtk = pManMR->pNtk;
+  Abc_Obj_t *pBiasNode, *pObj, *pNext, *pNext2;
+  InitConstraint_t *pConstraint;
+  int i, j, k, l, id;
+  const int nConstraints = Vec_PtrSize( pManMR->vInitConstraints );
+
+  pManMR->pDataArray = REALLOC( Flow_Data_t, pManMR->pDataArray, pManMR->nNodes + (nConstraints*(pManMR->iteration+1)) );
+  memset(pManMR->pDataArray + pManMR->nNodes, 0, sizeof(Flow_Data_t)*(nConstraints*(pManMR->iteration+1)));
+
+  vprintf("\t\tcreating %d bias structures\n", nConstraints);
+
+  Vec_PtrForEachEntry( pManMR->vInitConstraints, pConstraint, i ) {
+    if (pConstraint->pBiasNode) continue;
+    
+ //   printf("\t\t\tbias %d...\n", i);
+    pBiasNode = Abc_NtkCreateBlackbox( pNtk );
+
+    Vec_IntForEachEntry( &pConstraint->vNodes, id, j ) {
+      pObj = Abc_NtkObj(pNtk, id);
+      Abc_FlowRetime_ConnectBiasNode(pBiasNode, pObj, Vec_IntEntry(&pConstraint->vLags, j));
+    }
+
+    // pConstraint->pBiasNode = pBiasNode;
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Clears mapping from init node to original node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_ClearInitToOrig( Abc_Obj_t *pInit )
+{
+  int id = Abc_ObjId( pInit );
+  
+  // grow data structure if necessary
+  if (id >= pManMR->sizeInitToOrig) {
+    int oldSize = pManMR->sizeInitToOrig;
+    pManMR->sizeInitToOrig = 1.5*id + 10;
+    pManMR->pInitToOrig = realloc(pManMR->pInitToOrig, sizeof(NodeLag_t)*pManMR->sizeInitToOrig);
+    memset( &(pManMR->pInitToOrig[oldSize]), 0, sizeof(NodeLag_t)*(pManMR->sizeInitToOrig-oldSize) );
+  }
+  assert( pManMR->pInitToOrig );
+
+  pManMR->pInitToOrig[id].id = -1;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Sets mapping from init node to original node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_SetInitToOrig( Abc_Obj_t *pInit, Abc_Obj_t *pOrig)
+{
+  int lag;
+  int id = Abc_ObjId( pInit );
+  
+  // grow data structure if necessary
+  if (id >= pManMR->sizeInitToOrig) {
+    int oldSize = pManMR->sizeInitToOrig;
+    pManMR->sizeInitToOrig = 1.5*id + 10;
+    pManMR->pInitToOrig = realloc(pManMR->pInitToOrig, sizeof(NodeLag_t)*pManMR->sizeInitToOrig);
+    memset( &(pManMR->pInitToOrig[oldSize]), 0, sizeof(NodeLag_t)*(pManMR->sizeInitToOrig-oldSize) );
+  }
+  assert( pManMR->pInitToOrig );
+
+  // ignore BI, BO, and latch nodes
+  if (Abc_ObjIsBo(pOrig) || Abc_ObjIsBi(pOrig) || Abc_ObjIsLatch(pOrig)) {
+    Abc_FlowRetime_ClearInitToOrig(pInit);
+    return;
+  }
+
+  // move out of latch boxes
+  lag = Abc_FlowRetime_ObjFirstNonLatchBox(pOrig, &pOrig);
+
+  pManMR->pInitToOrig[id].id = Abc_ObjId(pOrig);
+  pManMR->pInitToOrig[id].lag = Abc_FlowRetime_GetLag(pOrig) + lag;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Gets mapping from init node to original node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_GetInitToOrig( Abc_Obj_t *pInit, Abc_Obj_t **pOrig, int *lag ) {
+
+  int id = Abc_ObjId( pInit );
+  int origId;
+
+  assert(id < pManMR->sizeInitToOrig);
+
+  origId = pManMR->pInitToOrig[id].id;
+
+  if (origId < 0) {
+    assert(Abc_ObjFaninNum(pInit));
+    Abc_FlowRetime_GetInitToOrig( Abc_ObjFanin0(pInit), pOrig, lag);
+    return;
+  }
+
+  *pOrig = Abc_NtkObj(pManMR->pNtk, origId);
+  *lag = pManMR->pInitToOrig[id].lag;
 }
diff --git a/src/opt/fret/fretMain.c b/src/opt/fret/fretMain.c
index 780c1f6f..a9ba8c4b 100644
--- a/src/opt/fret/fretMain.c
+++ b/src/opt/fret/fretMain.c
@@ -28,18 +28,22 @@
 
 static void Abc_FlowRetime_AddDummyFanin( Abc_Obj_t * pObj );
 
-static void Abc_FlowRetime_MainLoop( );
+static Abc_Ntk_t* Abc_FlowRetime_MainLoop( );
 
 static void Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk );
 static void Abc_FlowRetime_MarkReachable_rec( Abc_Obj_t * pObj, char end );
 static int  Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk );
 static void  Abc_FlowRetime_RemoveLatchBubbles( Abc_Obj_t * pLatch );
 
+static Abc_Ntk_t* Abc_FlowRetime_NtkDup( Abc_Ntk_t * pNtk );
+
 static void Abc_FlowRetime_VerifyPathLatencies( Abc_Ntk_t * pNtk );
 static int  Abc_FlowRetime_VerifyPathLatencies_rec( Abc_Obj_t * pObj, int markD );
 
+static void Abc_FlowRetime_UpdateLags_forw_rec( Abc_Obj_t *pObj );
+static void Abc_FlowRetime_UpdateLags_back_rec( Abc_Obj_t *pObj );
+
 extern void Abc_NtkMarkCone_rec( Abc_Obj_t * pObj, int fForward );
-extern Abc_Ntk_t * Abc_NtkRestrash( Abc_Ntk_t * pNtk, bool fCleanup );
 
 void
 print_node3(Abc_Obj_t *pObj);
@@ -64,12 +68,14 @@ int          fPathError = 0;
 
 ***********************************************************************/
 Abc_Ntk_t *
-Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
+Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, 
+                       int fComputeInitState, int fGuaranteeInitState, int fBlockConst,
                        int fForwardOnly, int fBackwardOnly, int nMaxIters,
                        int maxDelay, int fFastButConservative ) {
 
   int i;
   Abc_Obj_t   *pObj, *pNext;
+  InitConstraint_t *pData;
 
   // create manager
   pManMR = ALLOC( MinRegMan_t, 1 );
@@ -77,7 +83,8 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
   pManMR->pNtk = pNtk;
   pManMR->fVerbose = fVerbose;
   pManMR->fComputeInitState = fComputeInitState;
-  pManMR->fGuaranteeInitState = 0;
+  pManMR->fGuaranteeInitState = fGuaranteeInitState;
+  pManMR->fBlockConst = fBlockConst;
   pManMR->fForwardOnly = fForwardOnly;
   pManMR->fBackwardOnly = fBackwardOnly;
   pManMR->nMaxIters = nMaxIters;
@@ -85,6 +92,10 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
   pManMR->fComputeInitState = fComputeInitState;
   pManMR->fConservTimingOnly = fFastButConservative;
   pManMR->vNodes = Vec_PtrAlloc(100);
+  pManMR->vInitConstraints = Vec_PtrAlloc(2);
+  pManMR->pInitNtk = NULL;
+  pManMR->pInitToOrig = NULL;
+  pManMR->sizeInitToOrig = 0;
 
   vprintf("Flow-based minimum-register retiming...\n");  
 
@@ -96,7 +107,7 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
   if (maxDelay) {
     vprintf("\tmax delay constraint = %d\n", maxDelay);
     if (maxDelay < (i = Abc_NtkLevel(pNtk))) {
-      printf("ERROR: max delay constraint must be > current max delay (%d)\n", i);
+      printf("ERROR: max delay constraint (%d) must be > current max delay (%d)\n", maxDelay, i);
       return pNtk;
     }
   }
@@ -151,19 +162,18 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
   if (maxDelay)
     Abc_FlowRetime_InitTiming( pNtk );
 
-  // create Flow_Data structure
+  // create lag and Flow_Data structure
+  pManMR->vLags = Vec_IntStart(pManMR->nNodes);
+  memset(pManMR->vLags->pArray, 0, sizeof(int)*pManMR->nNodes);
+
   pManMR->pDataArray = ALLOC( Flow_Data_t, pManMR->nNodes );
   Abc_FlowRetime_ClearFlows( 1 );
-  Abc_NtkForEachObj( pNtk, pObj, i )
-    Abc_ObjSetCopy( pObj, (void *)(&pManMR->pDataArray[i]) );
 
   // main loop!
-  Abc_FlowRetime_MainLoop();
+  pNtk = Abc_FlowRetime_MainLoop();
 
-  // clear pCopy field
+  // cleanup node fields
   Abc_NtkForEachObj( pNtk, pObj, i ) {
-    Abc_ObjSetCopy( pObj, NULL );
-
     // if not computing init state, set all latches to DC
     if (!fComputeInitState && Abc_ObjIsLatch(pObj))
       Abc_LatchSetInitDc(pObj);
@@ -171,14 +181,24 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
 
   // deallocate space
   FREE( pManMR->pDataArray );
+  if (pManMR->pInitToOrig) FREE( pManMR->pInitToOrig );
   if (pManMR->vNodes) Vec_PtrFree(pManMR->vNodes);
+  if (pManMR->vLags) Vec_IntFree(pManMR->vLags);
   if (pManMR->vSinkDistHist) Vec_IntFree(pManMR->vSinkDistHist);
   if (pManMR->maxDelay) Abc_FlowRetime_FreeTiming( pNtk );
+  while( Vec_PtrSize( pManMR->vInitConstraints )) {
+    pData = Vec_PtrPop( pManMR->vInitConstraints );
+    //assert( pData->pBiasNode );
+    //Abc_NtkDeleteObj( pData->pBiasNode );
+    FREE( pData->vNodes.pArray );
+    FREE( pData );
+  }
+  FREE( pManMR->vInitConstraints );
 
   // restrash if necessary
   if (Abc_NtkIsStrash(pNtk)) {
     Abc_NtkReassignIds( pNtk );
-    pNtk = Abc_NtkRestrash( pNtk, 1 );
+    pNtk = Abc_FlowRetime_NtkSilentRestrash( pNtk, 1 );
   }
   
   vprintf("\tfinal reg count = %d\n", Abc_NtkLatchNum(pNtk));
@@ -205,10 +225,10 @@ Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
   SeeAlso     []
 
 ***********************************************************************/
-void
+Abc_Ntk_t *
 Abc_FlowRetime_MainLoop( ) {
-  Abc_Ntk_t *pNtk = pManMR->pNtk;
-  // Abc_Obj_t *pObj; int i;
+  Abc_Ntk_t *pNtk = pManMR->pNtk, *pNtkCopy = pNtk;
+  Abc_Obj_t *pObj; int i;
   int last, flow = 0, cut;
 
   // (i) forward retiming loop
@@ -237,30 +257,20 @@ Abc_FlowRetime_MainLoop( ) {
 
     cut = Abc_FlowRetime_ImplementCut( pNtk );
 
+#if defined (DEBUG_PRINT_LEVELS)
     vprintf("\t\tlevels = %d\n", Abc_NtkLevel(pNtk));
-
-#if 0
-    Abc_NtkForEachObj( pNtk, pObj, i ) pObj->Level = 0;
-
-    Abc_NtkLevel(pNtk);
-    Abc_NtkForEachObj( pNtk, pObj, i )
-      if (pObj->Level > pManMR->maxDelay) {
-        print_node( pObj );
-        Vec_PtrForEachEntry( FTIMEEDGES(pObj), p2,j ) {
-          printf(":%d ", p2->Id);
-        }
-      }
-    Abc_NtkLevelReverse(pNtk);
-    Abc_NtkForEachObj( pNtk, pObj, i )
-      if (pObj->Level > pManMR->maxDelay) {
-        print_node( pObj );
-      }
 #endif
 
     Abc_FlowRetime_ClearFlows( 1 );
 
     pManMR->iteration++;
   } while( cut != last );
+  
+  // intermediate cleanup (for strashed networks)
+  if (Abc_NtkIsStrash(pNtk)) {
+    Abc_NtkReassignIds( pNtk );
+    pNtk = pManMR->pNtk = Abc_FlowRetime_NtkSilentRestrash( pNtk, 1 );
+  }
 
   // print info about initial states
   if (pManMR->fComputeInitState && pManMR->fVerbose)
@@ -268,10 +278,18 @@ Abc_FlowRetime_MainLoop( ) {
 
   // (ii) backward retiming loop
   pManMR->fIsForward = 0;
-  pManMR->iteration = 0;
 
   if (!pManMR->fForwardOnly) do {
     // initializability loop
+    pManMR->iteration = 0;
+
+    // copy/restore network
+    if (pManMR->fGuaranteeInitState) {
+      if ( pNtk != pNtkCopy )
+        Abc_NtkDelete( pNtk );
+      pNtk = pManMR->pNtk = Abc_FlowRetime_NtkDup( pNtkCopy );
+      vprintf("\trestoring network. regs = %d\n", Abc_NtkLatchNum( pNtk ));
+    }
 
     if (pManMR->fComputeInitState) {
       Abc_FlowRetime_SetupBackwardInit( pNtk );
@@ -284,8 +302,9 @@ Abc_FlowRetime_MainLoop( ) {
       vprintf("\tbackward iteration %d\n", pManMR->iteration);
       last = Abc_NtkLatchNum( pNtk );
 
+      Abc_FlowRetime_AddInitBias( );
       Abc_FlowRetime_MarkBlocks( pNtk );
-      
+
       if (pManMR->maxDelay) {
         // timing-constrained loop
         Abc_FlowRetime_ConstrainConserv( pNtk );
@@ -296,25 +315,13 @@ Abc_FlowRetime_MainLoop( ) {
       } else {
         flow = Abc_FlowRetime_PushFlows( pNtk, 1 );
       }
-      
+
+      Abc_FlowRetime_RemoveInitBias( );
       cut = Abc_FlowRetime_ImplementCut( pNtk );
 
+#if defined(DEBUG_PRINT_LEVELS)
       vprintf("\t\tlevels = %d\n", Abc_NtkLevelReverse(pNtk));
-      
-#if 0
-    Abc_NtkForEachObj( pNtk, pObj, i ) pObj->Level = 0;
-
-    Abc_NtkLevel(pNtk);
-    Abc_NtkForEachObj( pNtk, pObj, i )
-      if (pObj->Level > pManMR->maxDelay) {
-        print_node( pObj );
-      }
-    Abc_NtkLevelReverse(pNtk);
-    Abc_NtkForEachObj( pNtk, pObj, i )
-      if (pObj->Level > pManMR->maxDelay) {
-        print_node( pObj );
-      }
-#endif
+#endif      
 
       Abc_FlowRetime_ClearFlows( 1 );
 
@@ -328,10 +335,23 @@ Abc_FlowRetime_MainLoop( ) {
       if (pManMR->fVerbose) Abc_FlowRetime_PrintInitStateInfo( pNtk );
       break;
     } else {
-      if (!pManMR->fGuaranteeInitState) break;
+      if (!pManMR->fGuaranteeInitState) {
+        printf("WARNING: no equivalent init state. setting all initial states to don't-cares\n");
+        Abc_NtkForEachLatch( pNtk, pObj, i ) Abc_LatchSetInitDc( pObj );
+        break;
+      }
       Abc_FlowRetime_ConstrainInit( );
     }
+    
+    Abc_NtkDelete(pManMR->pInitNtk);
+    pManMR->pInitNtk = NULL;
   } while(1);
+
+  assert(!pManMR->fComputeInitState || pManMR->pInitNtk);
+  if (pManMR->fComputeInitState)   Abc_NtkDelete(pManMR->pInitNtk);
+  if (pManMR->fGuaranteeInitState) ; /* Abc_NtkDelete(pNtkCopy); note: original ntk deleted later */
+
+  return pNtk;
 }
 
 
@@ -369,7 +389,7 @@ Abc_FlowRetime_RemoveLatchBubbles( Abc_Obj_t * pLatch ) {
   pBi->fCompl0 ^= bubble ^ Abc_ObjFaninC0(pLatch);
 
   // convert bubble to INV if not AIG
-  if (!Abc_NtkHasAig( pNtk ) && Abc_ObjFaninC0(pBi)) {
+  if (!Abc_NtkIsStrash( pNtk ) && Abc_ObjFaninC0(pBi)) {
     pBi->fCompl0 = 0;
     pInv = Abc_NtkCreateNodeInv( pNtk, Abc_ObjFanin0(pBi) );
     Abc_ObjPatchFanin( pBi, Abc_ObjFanin0(pBi), pInv );
@@ -397,6 +417,8 @@ Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk ) {
   Abc_Obj_t *pObj;
 
   if (pManMR->fIsForward){
+    // --- forward retiming : block TFO of inputs    
+
     // mark the frontier
     Abc_NtkForEachPo( pNtk, pObj, i )
       pObj->fMarkA = 1;
@@ -408,6 +430,8 @@ Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk ) {
     Abc_NtkForEachPi( pNtk, pObj, i )
       Abc_NtkMarkCone_rec( pObj, pManMR->fIsForward );
   } else {
+    // --- backward retiming : block TFI of outputs
+
     // mark the frontier
     Abc_NtkForEachPi( pNtk, pObj, i )
       pObj->fMarkA = 1;
@@ -418,6 +442,14 @@ Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk ) {
     // mark the nodes reachable from the POs
     Abc_NtkForEachPo( pNtk, pObj, i )
       Abc_NtkMarkCone_rec( pObj, pManMR->fIsForward );
+    // block constant nodes (if enabled)
+    if (pManMR->fBlockConst) {
+      Abc_NtkForEachObj( pNtk, pObj, i )
+        if ((Abc_NtkIsStrash(pNtk) && Abc_AigNodeIsConst(pObj)) ||
+            (!Abc_NtkIsStrash(pNtk) && Abc_NodeIsConst(pObj))) {
+          FSET(pObj, BLOCK);
+        }
+    }
   }
 
   // copy marks
@@ -518,7 +550,7 @@ Abc_FlowRetime_FixLatchBoxes( Abc_Ntk_t *pNtk, Vec_Ptr_t *vBoxIns ) {
     pBi = (Abc_Obj_t *)Vec_PtrPop( vBoxIns );
     assert(Abc_ObjIsBi(pBi));
     assert(Abc_ObjFanoutNum(pBi) == 1);
-    assert(Abc_ObjFaninNum(pBi) == 1);
+    // APH: broken by bias nodes assert(Abc_ObjFaninNum(pBi) == 1);
     pBo = Abc_ObjFanout0(pBi);
     assert(!Abc_ObjFaninC0(pBo));
 
@@ -546,7 +578,12 @@ Abc_FlowRetime_FixLatchBoxes( Abc_Ntk_t *pNtk, Vec_Ptr_t *vBoxIns ) {
       assert(Abc_ObjFanoutNum(pBi) == 0);
       assert(Abc_ObjFaninNum(pBo) == 0);
       assert(Abc_ObjFanoutNum(pBo) == 0);
-    } else assert(Abc_ObjIsLatch(pBo));
+    } else if (Abc_ObjIsLatch(pBo)) {
+    } else {
+      Abc_ObjPrint(stdout, pBi);
+      Abc_ObjPrint(stdout, pBo);
+      assert(0);
+    }
   }
 
   // 2. add bi/bos as necessary for latches
@@ -803,6 +840,7 @@ Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk ) {
   // insert latches into netlist
   Abc_NtkForEachObj( pNtk, pObj, i ) {
     if (Abc_ObjIsLatch( pObj )) continue;
+    if (FTEST(pObj, BIAS_NODE)) continue;
     
     // a latch is required on every node that lies across the min-cit
     assert(!pManMR->fIsForward || !FTEST(pObj, VISITED_E) || FTEST(pObj, VISITED_R));
@@ -837,7 +875,7 @@ Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk ) {
         if (Abc_ObjIsBi(pNext)) assert(Abc_ObjFaninNum(pNext) == 1);
 
       }
-      if (Abc_ObjIsBi(pObj)) assert(Abc_ObjFaninNum(pObj) == 1);
+      // APH: broken by bias nodes  if (Abc_ObjIsBi(pObj)) assert(Abc_ObjFaninNum(pObj) == 1);
     }
   }
 
@@ -852,6 +890,7 @@ Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk ) {
   }
   
   // update initial states
+  Abc_FlowRetime_UpdateLags( );
   Abc_FlowRetime_InitState( pNtk );
 
   // restore latch boxes
@@ -881,7 +920,7 @@ void
 Abc_FlowRetime_AddDummyFanin( Abc_Obj_t * pObj ) {
   Abc_Ntk_t *pNtk = Abc_ObjNtk( pObj );
 
-  if (Abc_NtkHasAig(pNtk)) 
+  if (Abc_NtkIsStrash(pNtk)) 
     Abc_ObjAddFanin(pObj, Abc_AigConst1( pNtk ));
   else
     Abc_ObjAddFanin(pObj, Abc_NtkCreateNodeConst0( pNtk ));
@@ -1057,3 +1096,281 @@ void Abc_FlowRetime_ClearFlows( bool fClearAll ) {
     }
   }
 }
+
+
+/**Function*************************************************************
+
+  Synopsis    [Duplicates network.]
+
+  Description [Duplicates any type of network. Preserves copy data.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+static Abc_Ntk_t* Abc_FlowRetime_NtkDup( Abc_Ntk_t * pNtk ) {
+  Abc_Ntk_t *pNtkCopy;
+  Abc_Obj_t *pObj, *pObjCopy, *pNext, *pNextCopy;
+  int i, j;
+
+  pNtkCopy = Abc_NtkAlloc( pNtk->ntkType, pNtk->ntkFunc, 1 );
+
+  // copy each object
+  Abc_NtkForEachObj( pNtk, pObj, i) {
+
+    if (Abc_NtkIsStrash( pNtk ) && Abc_AigNodeIsConst( pObj ))
+      pObjCopy = Abc_AigConst1( pNtkCopy );
+    else
+      pObjCopy = Abc_NtkDupObj( pNtkCopy, pObj, 0 );
+
+    FDATA( pObj )->pCopy = pObjCopy;
+    FDATA( pObj )->mark = 0;
+
+    // assert( pManMR->fIsForward || pObj->Id == pObjCopy->Id );
+
+    // copy complementation
+    pObjCopy->fCompl0 = pObj->fCompl0;
+    pObjCopy->fCompl1 = pObj->fCompl1;
+    pObjCopy->fPhase = pObj->fPhase;
+  }
+
+  // connect fanin
+  Abc_NtkForEachObj( pNtk, pObj, i) {
+    pObjCopy = FDATA(pObj)->pCopy;
+    assert(pObjCopy);
+    Abc_ObjForEachFanin( pObj, pNext, j ) {
+      pNextCopy = FDATA(pNext)->pCopy;
+      assert(pNextCopy);
+      assert(pNext->Type == pNextCopy->Type);
+
+      Abc_ObjAddFanin(pObjCopy, pNextCopy);
+    }
+  }
+
+#if defined(DEBUG_CHECK) || 1
+  Abc_NtkForEachObj( pNtk, pObj, i) { 
+    pObjCopy = FDATA(pObj)->pCopy;
+    assert( Abc_ObjFanoutNum( pObj ) ==  Abc_ObjFanoutNum( pObjCopy ) );
+    assert( Abc_ObjFaninNum( pObj ) ==  Abc_ObjFaninNum( pObjCopy ) );
+  }
+#endif
+
+  assert(Abc_NtkObjNum( pNtk )   == Abc_NtkObjNum( pNtkCopy ) );
+  assert(Abc_NtkLatchNum( pNtk ) == Abc_NtkLatchNum( pNtkCopy ) );
+  assert(Abc_NtkPoNum( pNtk )    == Abc_NtkPoNum( pNtkCopy ) );
+  assert(Abc_NtkPiNum( pNtk )    == Abc_NtkPiNum( pNtkCopy ) );
+
+  return pNtkCopy;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Silent restrash.]
+
+  Description [Same functionality as Abc_NtkRestrash but w/o warnings.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+Abc_Ntk_t * Abc_FlowRetime_NtkSilentRestrash( Abc_Ntk_t * pNtk, bool fCleanup )
+{
+    Abc_Ntk_t * pNtkAig;
+    Abc_Obj_t * pObj;
+    int i, nNodes;//, RetValue;
+    assert( Abc_NtkIsStrash(pNtk) );
+    // start the new network (constants and CIs of the old network will point to the their counterparts in the new network)
+    pNtkAig = Abc_NtkStartFrom( pNtk, ABC_NTK_STRASH, ABC_FUNC_AIG );
+    // restrash the nodes (assuming a topological order of the old network)
+    Abc_NtkForEachNode( pNtk, pObj, i )
+        pObj->pCopy = Abc_AigAnd( pNtkAig->pManFunc, Abc_ObjChild0Copy(pObj), Abc_ObjChild1Copy(pObj) );
+    // finalize the network
+    Abc_NtkFinalize( pNtk, pNtkAig );
+    // perform cleanup if requested
+    if ( fCleanup )
+      nNodes = Abc_AigCleanup(pNtkAig->pManFunc);
+    // duplicate EXDC 
+    if ( pNtk->pExdc )
+      pNtkAig->pExdc = Abc_NtkDup( pNtk->pExdc );
+    // make sure everything is okay
+    if ( !Abc_NtkCheck( pNtkAig ) )
+      {
+        printf( "Abc_NtkStrash: The network check has failed.\n" );
+        Abc_NtkDelete( pNtkAig );
+        return NULL;
+      }
+    return pNtkAig;
+}
+
+
+
+/**Function*************************************************************
+
+  Synopsis    [Updates lag values.]
+
+  Description [Recursive.  Forward retiming.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_UpdateLags_forw_rec( Abc_Obj_t *pObj ) {
+  Abc_Obj_t *pNext;
+  int i;
+
+  assert(!Abc_ObjIsPi(pObj));
+  assert(!Abc_ObjIsLatch(pObj));
+
+  if (Abc_ObjIsBo(pObj)) return;
+  if (Abc_NodeIsTravIdCurrent(pObj)) return;
+
+  Abc_NodeSetTravIdCurrent(pObj);
+
+  if (Abc_ObjIsNode(pObj)) {
+    Abc_FlowRetime_SetLag( pObj, -1+Abc_FlowRetime_GetLag(pObj) );
+  }
+
+  Abc_ObjForEachFanin( pObj, pNext, i ) {
+    Abc_FlowRetime_UpdateLags_forw_rec( pNext );
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Updates lag values.]
+
+  Description [Recursive.  Backward retiming.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_UpdateLags_back_rec( Abc_Obj_t *pObj ) {
+  Abc_Obj_t *pNext;
+  int i;
+
+  assert(!Abc_ObjIsPo(pObj));
+  assert(!Abc_ObjIsLatch(pObj));
+
+  if (Abc_ObjIsBo(pObj)) return;
+  if (Abc_NodeIsTravIdCurrent(pObj)) return;
+
+  Abc_NodeSetTravIdCurrent(pObj);
+
+  if (Abc_ObjIsNode(pObj)) {
+    Abc_FlowRetime_SetLag( pObj, 1+Abc_FlowRetime_GetLag(pObj) );
+  }
+
+  Abc_ObjForEachFanout( pObj, pNext, i ) {
+    Abc_FlowRetime_UpdateLags_back_rec( pNext );
+  }
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Updates lag values.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_UpdateLags( ) {
+  Abc_Obj_t *pObj, *pNext;
+  int i, j;
+
+  Abc_NtkIncrementTravId( pManMR->pNtk );
+
+  Abc_NtkForEachLatch( pManMR->pNtk, pObj, i )
+    if (pManMR->fIsForward) {
+      Abc_ObjForEachFanin( pObj, pNext, j )          
+        Abc_FlowRetime_UpdateLags_forw_rec( pNext );
+    } else {
+      Abc_ObjForEachFanout( pObj, pNext, j )          
+        Abc_FlowRetime_UpdateLags_back_rec( pNext );
+    }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Gets lag value of a node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+int 
+Abc_FlowRetime_GetLag( Abc_Obj_t *pObj ) {
+  assert( !Abc_ObjIsLatch(pObj) );
+  assert( Abc_ObjId(pObj) < Vec_IntSize(pManMR->vLags) );
+
+  return Vec_IntEntry(pManMR->vLags, Abc_ObjId(pObj));
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Sets lag value of a node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void 
+Abc_FlowRetime_SetLag( Abc_Obj_t *pObj, int lag ) {
+  assert( Abc_ObjIsNode(pObj) );
+  assert( Abc_ObjId(pObj) < Vec_IntSize(pManMR->vLags) );
+
+  Vec_IntWriteEntry(pManMR->vLags, Abc_ObjId(pObj), lag);
+}
+
+
+static void Abc_ObjPrintNeighborhood_rec( Abc_Obj_t *pObj, Vec_Ptr_t *vNodes, int depth ) {
+  Abc_Obj_t *pObj2;
+  int i;
+  
+  if (pObj->fMarkC || depth < 0) return;
+
+  pObj->fMarkC = 1;
+  Vec_PtrPush( vNodes, pObj );
+
+  Abc_ObjPrint( stdout, pObj );
+
+  Abc_ObjForEachFanout(pObj, pObj2, i) {
+    Abc_ObjPrintNeighborhood_rec( pObj2, vNodes, depth-1 );
+  }
+  Abc_ObjForEachFanin(pObj, pObj2, i) {
+    Abc_ObjPrintNeighborhood_rec( pObj2, vNodes, depth-1 );
+  }
+}
+
+void Abc_ObjPrintNeighborhood( Abc_Obj_t *pObj, int depth ) {
+  Vec_Ptr_t *vNodes = Vec_PtrAlloc(100); 
+  Abc_Obj_t *pObj2;
+
+  Abc_ObjPrintNeighborhood_rec( pObj, vNodes, depth );
+
+  while(Vec_PtrSize(vNodes)) {
+    pObj2 = Vec_PtrPop(vNodes);
+    pObj2->fMarkC = 0;
+  }
+
+  Vec_PtrFree(vNodes);
+}
diff --git a/src/opt/fret/fretime.h b/src/opt/fret/fretime.h
index 167543ce..bbb79d26 100644
--- a/src/opt/fret/fretime.h
+++ b/src/opt/fret/fretime.h
@@ -27,7 +27,8 @@
 // #define DEBUG_PRINT_FLOWS
 // #define DEBUG_VISITED
 // #define DEBUG_PREORDER
-// #define DEBUG_CHECK
+#define DEBUG_CHECK
+// #define DEBUG_PRINT_LEVELS
 
 ////////////////////////////////////////////////////////////////////////
 ///                        DECLARATIONS                              ///
@@ -36,17 +37,18 @@
 #define MAX_DIST 30000
 
 // flags in Flow_Data structure...
-#define VISITED_E       0x01
-#define VISITED_R       0x02
+#define VISITED_E       0x001
+#define VISITED_R       0x002
 #define VISITED  (VISITED_E | VISITED_R)
-#define FLOW            0x04
-#define CROSS_BOUNDARY  0x08
-#define BLOCK           0x10
-#define INIT_0          0x20
-#define INIT_1          0x40
+#define FLOW            0x004
+#define CROSS_BOUNDARY  0x008
+#define BLOCK           0x010
+#define INIT_0          0x020
+#define INIT_1          0x040
 #define INIT_CARE (INIT_0 | INIT_1)
-#define CONSERVATIVE    0x80
+#define CONSERVATIVE    0x080
 #define BLOCK_OR_CONS (BLOCK | CONSERVATIVE)
+#define BIAS_NODE       0x100
 
 typedef struct Flow_Data_t_ {
   unsigned int mark : 16;
@@ -55,6 +57,7 @@ typedef struct Flow_Data_t_ {
     Abc_Obj_t   *pred;
     /* unsigned int var; */
     Abc_Obj_t   *pInitObj;
+    Abc_Obj_t   *pCopy;
     Vec_Ptr_t   *vNodes;
   };
 
@@ -63,26 +66,30 @@ typedef struct Flow_Data_t_ {
 } Flow_Data_t;
 
 // useful macros for manipulating Flow_Data structure...
-#define FDATA( x )     ((Flow_Data_t *)Abc_ObjCopy(x))
-#define FSET( x, y )   ((Flow_Data_t *)Abc_ObjCopy(x))->mark |= y
-#define FUNSET( x, y ) ((Flow_Data_t *)Abc_ObjCopy(x))->mark &= ~y
-#define FTEST( x, y )  (((Flow_Data_t *)Abc_ObjCopy(x))->mark & y)
+#define FDATA( x )     (pManMR->pDataArray+Abc_ObjId(x))
+#define FSET( x, y )   FDATA(x)->mark |= y
+#define FUNSET( x, y ) FDATA(x)->mark &= ~y
+#define FTEST( x, y )  (FDATA(x)->mark & y)
 #define FTIMEEDGES( x )  &(pManMR->vTimeEdges[Abc_ObjId( x )])
 
-static inline void FSETPRED(Abc_Obj_t *pObj, Abc_Obj_t *pPred) {
-  assert(!Abc_ObjIsLatch(pObj)); // must preserve field to maintain init state linkage
-  FDATA(pObj)->pred = pPred;
-}
-static inline Abc_Obj_t * FGETPRED(Abc_Obj_t *pObj) {
-  return FDATA(pObj)->pred;
-}
+typedef struct NodeLag_T_ {
+  int id;
+  int lag;
+} NodeLag_t;
 
+typedef struct InitConstraint_t_ {
+  Abc_Obj_t *pBiasNode;
+
+  Vec_Int_t  vNodes;
+  Vec_Int_t  vLags;
+
+} InitConstraint_t;
 
 typedef struct MinRegMan_t_ {
  
   // problem description:
   int         maxDelay;
-  bool        fComputeInitState, fGuaranteeInitState;
+  bool        fComputeInitState, fGuaranteeInitState, fBlockConst;
   int         nNodes, nLatches;
   bool        fForwardOnly, fBackwardOnly;
   bool        fConservTimingOnly;
@@ -99,24 +106,38 @@ typedef struct MinRegMan_t_ {
   int         fSolutionIsDc;
   int         constraintMask;
   int         iteration, subIteration;
+  Vec_Int_t  *vLags;
   
   // problem data
   Vec_Int_t   *vSinkDistHist;
   Flow_Data_t *pDataArray;
   Vec_Ptr_t   *vTimeEdges;
   Vec_Ptr_t   *vExactNodes;
+  Vec_Ptr_t   *vInitConstraints;
   Abc_Ntk_t   *pInitNtk;
   Vec_Ptr_t   *vNodes; // re-useable struct
-
+  
+  NodeLag_t   *pInitToOrig;
+  int          sizeInitToOrig;
+  
 } MinRegMan_t ;
 
+extern MinRegMan_t *pManMR;
+
 #define vprintf if (pManMR->fVerbose) printf 
 
+static inline void FSETPRED(Abc_Obj_t *pObj, Abc_Obj_t *pPred) {
+  assert(!Abc_ObjIsLatch(pObj)); // must preserve field to maintain init state linkage
+  FDATA(pObj)->pred = pPred;
+}
+static inline Abc_Obj_t * FGETPRED(Abc_Obj_t *pObj) {
+  return FDATA(pObj)->pred;
+}
+
 /*=== fretMain.c ==========================================================*/
- 
-extern MinRegMan_t *pManMR;
 
-Abc_Ntk_t *    Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
+Abc_Ntk_t *    Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose,
+                                      int fComputeInitState, int fGuaranteeInitState, int fBlockConst,
                                       int fForward, int fBackward, int nMaxIters,
                                       int maxDelay, int fFastButConservative);
 
@@ -128,6 +149,15 @@ int  Abc_FlowRetime_PushFlows( Abc_Ntk_t * pNtk, bool fVerbose );
 bool Abc_FlowRetime_IsAcrossCut( Abc_Obj_t *pCur, Abc_Obj_t *pNext );
 void Abc_FlowRetime_ClearFlows( bool fClearAll );
 
+int  Abc_FlowRetime_GetLag( Abc_Obj_t *pObj );
+void Abc_FlowRetime_SetLag( Abc_Obj_t *pObj, int lag );
+
+void Abc_FlowRetime_UpdateLags( );
+
+void Abc_ObjPrintNeighborhood( Abc_Obj_t *pObj, int depth );
+
+Abc_Ntk_t * Abc_FlowRetime_NtkSilentRestrash( Abc_Ntk_t * pNtk, bool fCleanup );
+
 /*=== fretFlow.c ==========================================================*/
 
 int  dfsplain_e( Abc_Obj_t *pObj, Abc_Obj_t *pPred );
@@ -150,6 +180,8 @@ void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk );
 int  Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk );
 
 void Abc_FlowRetime_ConstrainInit(  );
+void Abc_FlowRetime_AddInitBias(  );
+void Abc_FlowRetime_RemoveInitBias(  );
 
 /*=== fretTime.c ==========================================================*/