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/**CFile****************************************************************
FileName [retDelay.c]
SystemName [ABC: Logic synthesis and verification system.]
PackageName [Retiming package.]
Synopsis [Incremental retiming for optimum delay.]
Author [Alan Mishchenko]
Affiliation [UC Berkeley]
Date [Ver. 1.0. Started - Oct 31, 2006.]
Revision [$Id: retDelay.c,v 1.00 2006/10/31 00:00:00 alanmi Exp $]
***********************************************************************/
#include "retInt.h"
////////////////////////////////////////////////////////////////////////
/// DECLARATIONS ///
////////////////////////////////////////////////////////////////////////
static int Abc_NtkRetimeMinDelayTry( Abc_Ntk_t * pNtk, int fForward, int fInitial, int nIterLimit, int * pIterBest, int fVerbose );
static int Abc_NtkRetimeTiming( Abc_Ntk_t * pNtk, int fForward, Vec_Ptr_t * vCritical );
static int Abc_NtkRetimeTiming_rec( Abc_Obj_t * pObj, int fForward );
////////////////////////////////////////////////////////////////////////
/// FUNCTION DEFINITIONS ///
////////////////////////////////////////////////////////////////////////
/**Function*************************************************************
Synopsis [Retimes incrementally for minimum delay.]
Description [This procedure cannot be called in the application code
because it assumes that the network is preprocessed by removing LIs/LOs.]
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeMinDelay( Abc_Ntk_t * pNtk, Abc_Ntk_t * pNtkCopy, int nIterLimit, int fForward, int fVerbose )
{
int IterBest, DelayBest;
int IterBest2, DelayBest2;
// try to find the best delay iteration on a copy
DelayBest = Abc_NtkRetimeMinDelayTry( pNtkCopy, fForward, 0, nIterLimit, &IterBest, fVerbose );
if ( IterBest == 0 )
return 1;
// perform the given number of iterations on the original network
DelayBest2 = Abc_NtkRetimeMinDelayTry( pNtk, fForward, 1, IterBest, &IterBest2, fVerbose );
assert( DelayBest == DelayBest2 );
assert( IterBest == IterBest2 );
return 1;
}
/**Function*************************************************************
Synopsis [Returns the best delay and the number of best iteration.]
Description []
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeMinDelayTry( Abc_Ntk_t * pNtk, int fForward, int fInitial, int nIterLimit, int * pIterBest, int fVerbose )
{
Abc_Ntk_t * pNtkNew = NULL;
Vec_Ptr_t * vCritical;
Vec_Int_t * vValues = NULL; // Suppress "might be used uninitialized"
Abc_Obj_t * pObj;
int i, k, IterBest, DelayCur, DelayBest;
int DelayStart = -1; // Suppress "might be used uninitialized"
int LatchesBest;
// transfer intitial values
if ( fInitial )
{
if ( fForward )
Abc_NtkRetimeTranferToCopy( pNtk );
else
{
// save initial value of the latches
vValues = Abc_NtkRetimeCollectLatchValues( pNtk );
// start the network for initial value computation
pNtkNew = Abc_NtkRetimeBackwardInitialStart( pNtk );
}
}
if ( fVerbose && !fInitial )
printf( "Performing analysis:\n" );
// find the best iteration
DelayBest = ABC_INFINITY; IterBest = 0; LatchesBest = Abc_NtkLatchNum(pNtk);
vCritical = Vec_PtrAlloc( 100 );
for ( i = 0; ; i++ )
{
// perform moves for the timing-critical nodes
DelayCur = Abc_NtkRetimeTiming( pNtk, fForward, vCritical );
if ( i == 0 )
DelayStart = DelayCur;
// record this position if it has the best delay
if ( DelayBest > DelayCur )
{
if ( fVerbose && !fInitial )
printf( "%s Iter = %3d. Delay = %3d. Latches = %5d. Delta = %6.2f. Ratio = %4.2f %%\n",
fForward ? "Fwd": "Bwd", i, DelayCur, Abc_NtkLatchNum(pNtk),
1.0*(Abc_NtkLatchNum(pNtk)-LatchesBest)/(DelayBest-DelayCur),
100.0*(Abc_NtkLatchNum(pNtk)-LatchesBest)/Abc_NtkLatchNum(pNtk)/(DelayBest-DelayCur) );
DelayBest = DelayCur;
IterBest = i;
LatchesBest = Abc_NtkLatchNum(pNtk);
}
// quit after timing analysis
if ( i == nIterLimit )
break;
// skip if 10 interations did not give improvement
if ( i - IterBest > 20 )
break;
// try retiming to improve the delay
Vec_PtrForEachEntry( vCritical, pObj, k )
if ( Abc_NtkRetimeNodeIsEnabled(pObj, fForward) )
Abc_NtkRetimeNode( pObj, fForward, fInitial );
// share latches
if ( !fForward )
Abc_NtkRetimeShareLatches( pNtk, fInitial );
}
Vec_PtrFree( vCritical );
// transfer the initial state back to the latches
if ( fInitial )
{
if ( fForward )
Abc_NtkRetimeTranferFromCopy( pNtk );
else
{
Abc_NtkRetimeBackwardInitialFinish( pNtk, pNtkNew, vValues, fVerbose );
Abc_NtkDelete( pNtkNew );
Vec_IntFree( vValues );
}
}
if ( fVerbose && !fInitial )
printf( "%s : Starting delay = %3d. Final delay = %3d. IterBest = %2d (out of %2d).\n",
fForward? "Forward " : "Backward", DelayStart, DelayBest, IterBest, nIterLimit );
*pIterBest = (nIterLimit == 1) ? 1 : IterBest;
return DelayBest;
}
/**Function*************************************************************
Synopsis [Returns the set of timing-critical nodes.]
Description [Performs static timing analysis on the network. Uses
unit-delay model.]
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeTiming( Abc_Ntk_t * pNtk, int fForward, Vec_Ptr_t * vCritical )
{
Vec_Ptr_t * vLatches;
Abc_Obj_t * pObj, * pNext;
int i, k, LevelCur, LevelMax = 0;
// mark all objects except nodes
Abc_NtkIncrementTravId(pNtk);
vLatches = Vec_PtrAlloc( Abc_NtkLatchNum(pNtk) );
Abc_NtkForEachObj( pNtk, pObj, i )
{
if ( Abc_ObjIsLatch(pObj) )
Vec_PtrPush( vLatches, pObj );
if ( Abc_ObjIsNode(pObj) )
continue;
pObj->Level = 0;
Abc_NodeSetTravIdCurrent( pObj );
}
// perform analysis from CIs/COs
if ( fForward )
{
Vec_PtrForEachEntry( vLatches, pObj, i )
{
Abc_ObjForEachFanout( pObj, pNext, k )
{
LevelCur = Abc_NtkRetimeTiming_rec( pNext, fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
}
Abc_NtkForEachPi( pNtk, pObj, i )
{
Abc_ObjForEachFanout( pObj, pNext, k )
{
LevelCur = Abc_NtkRetimeTiming_rec( pNext, fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
}
}
else
{
Vec_PtrForEachEntry( vLatches, pObj, i )
{
LevelCur = Abc_NtkRetimeTiming_rec( Abc_ObjFanin0(pObj), fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
Abc_NtkForEachPo( pNtk, pObj, i )
{
LevelCur = Abc_NtkRetimeTiming_rec( Abc_ObjFanin0(pObj), fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
}
// collect timing critical nodes, which should be retimed forward/backward
Vec_PtrClear( vCritical );
Abc_NtkIncrementTravId(pNtk);
if ( fForward )
{
Vec_PtrForEachEntry( vLatches, pObj, i )
{
Abc_ObjForEachFanout( pObj, pNext, k )
{
if ( Abc_NodeIsTravIdCurrent(pNext) )
continue;
if ( LevelMax != (int)pNext->Level )
continue;
// new critical node
Vec_PtrPush( vCritical, pNext );
Abc_NodeSetTravIdCurrent( pNext );
}
}
}
else
{
Vec_PtrForEachEntry( vLatches, pObj, i )
{
Abc_ObjForEachFanin( pObj, pNext, k )
{
if ( Abc_NodeIsTravIdCurrent(pNext) )
continue;
if ( LevelMax != (int)pNext->Level )
continue;
// new critical node
Vec_PtrPush( vCritical, pNext );
Abc_NodeSetTravIdCurrent( pNext );
}
}
}
Vec_PtrFree( vLatches );
return LevelMax;
}
/**Function*************************************************************
Synopsis [Recursively performs timing analysis.]
Description [Performs static timing analysis on the network. Uses
unit-delay model.]
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeTiming_rec( Abc_Obj_t * pObj, int fForward )
{
Abc_Obj_t * pNext;
int i, LevelCur, LevelMax = 0;
// skip visited nodes
if ( Abc_NodeIsTravIdCurrent(pObj) )
return pObj->Level;
Abc_NodeSetTravIdCurrent(pObj);
// visit the next nodes
if ( fForward )
{
Abc_ObjForEachFanout( pObj, pNext, i )
{
LevelCur = Abc_NtkRetimeTiming_rec( pNext, fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
}
else
{
Abc_ObjForEachFanin( pObj, pNext, i )
{
LevelCur = Abc_NtkRetimeTiming_rec( pNext, fForward );
if ( LevelMax < LevelCur )
LevelMax = LevelCur;
}
}
// printf( "Node %3d -> Level %3d.\n", pObj->Id, LevelMax + 1 );
pObj->Level = LevelMax + 1;
return pObj->Level;
}
////////////////////////////////////////////////////////////////////////
/// END OF FILE ///
////////////////////////////////////////////////////////////////////////
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