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/**CFile****************************************************************
FileName [abcSeqRetime.c]
SystemName [ABC: Logic synthesis and verification system.]
PackageName [Network and node package.]
Synopsis [Peforms retiming for optimal clock cycle.]
Author [Alan Mishchenko]
Affiliation [UC Berkeley]
Date [Ver. 1.0. Started - June 20, 2005.]
Revision [$Id: abcSeqRetime.c,v 1.00 2005/06/20 00:00:00 alanmi Exp $]
***********************************************************************/
#include "abc.h"
////////////////////////////////////////////////////////////////////////
/// DECLARATIONS ///
////////////////////////////////////////////////////////////////////////
// storing arrival times in the nodes
static inline int Abc_NodeReadLValue( Abc_Obj_t * pNode ) { return Vec_IntEntry( (pNode)->pNtk->pData, (pNode)->Id ); }
static inline void Abc_NodeSetLValue( Abc_Obj_t * pNode, int Value ) { Vec_IntWriteEntry( (pNode)->pNtk->pData, (pNode)->Id, (Value) ); }
// the internal procedures
static int Abc_NtkRetimeSearch_rec( Abc_Ntk_t * pNtk, int FiMin, int FiMax );
static int Abc_NtkRetimeForPeriod( Abc_Ntk_t * pNtk, int Fi );
static int Abc_NodeUpdateLValue( Abc_Obj_t * pObj, int Fi );
// node status after updating its arrival time
enum { ABC_UPDATE_FAIL, ABC_UPDATE_NO, ABC_UPDATE_YES };
////////////////////////////////////////////////////////////////////////
/// FUNCTION DEFITIONS ///
////////////////////////////////////////////////////////////////////////
/**Function*************************************************************
Synopsis [Retimes AIG for optimal delay.]
Description []
SideEffects []
SeeAlso []
***********************************************************************/
void Abc_NtkSeqRetimeDelay( Abc_Ntk_t * pNtk )
{
int FiMax, FiBest;
assert( Abc_NtkIsSeq( pNtk ) );
// start storage for sequential arrival times
assert( pNtk->pData == NULL );
pNtk->pData = Vec_IntAlloc( 0 );
// get the maximum possible clock
FiMax = Abc_NtkNodeNum(pNtk);
// make sure this clock period is feasible
assert( Abc_NtkRetimeForPeriod( pNtk, FiMax ) );
// search for the optimal clock period between 0 and nLevelMax
FiBest = Abc_NtkRetimeSearch_rec( pNtk, 0, FiMax );
// print the result
printf( "The best clock period is %3d.\n", FiBest );
// free storage
Vec_IntFree( pNtk->pData );
pNtk->pData = NULL;
}
/**Function*************************************************************
Synopsis [Performs binary search for the optimal clock period.]
Description [Assumes that FiMin is infeasible while FiMax is feasible.]
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeSearch_rec( Abc_Ntk_t * pNtk, int FiMin, int FiMax )
{
int Median;
assert( FiMin < FiMax );
if ( FiMin + 1 == FiMax )
return FiMax;
Median = FiMin + (FiMax - FiMin)/2;
if ( Abc_NtkRetimeForPeriod( pNtk, Median ) )
return Abc_NtkRetimeSearch_rec( pNtk, FiMin, Median ); // Median is feasible
else
return Abc_NtkRetimeSearch_rec( pNtk, Median, FiMax ); // Median is infeasible
}
/**Function*************************************************************
Synopsis [Returns 1 if retiming with this clock period is feasible.]
Description []
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NtkRetimeForPeriod( Abc_Ntk_t * pNtk, int Fi )
{
Vec_Ptr_t * vFrontier;
Abc_Obj_t * pObj, * pFanout;
int RetValue, i, k;
// set l-values of all nodes to be minus infinity
Vec_IntFill( pNtk->pData, Abc_NtkObjNumMax(pNtk), -ABC_INFINITY );
// start the frontier by including PI fanouts
vFrontier = Vec_PtrAlloc( 100 );
Abc_NtkForEachPi( pNtk, pObj, i )
{
Abc_NodeSetLValue( pObj, 0 );
Abc_ObjForEachFanout( pObj, pFanout, k )
if ( pFanout->fMarkA == 0 )
{
Vec_PtrPush( vFrontier, pFanout );
pFanout->fMarkA = 1;
}
}
// iterate until convergence
Vec_PtrForEachEntry( vFrontier, pObj, i )
{
RetValue = Abc_NodeUpdateLValue( pObj, Fi );
if ( RetValue == ABC_UPDATE_FAIL )
break;
// unmark the node as processed
pObj->fMarkA = 0;
if ( RetValue == ABC_UPDATE_NO )
continue;
assert( RetValue == ABC_UPDATE_YES );
// arrival times have changed - add fanouts to the frontier
Abc_ObjForEachFanout( pObj, pFanout, k )
if ( pFanout->fMarkA == 0 )
{
Vec_PtrPush( vFrontier, pFanout );
pFanout->fMarkA = 1;
}
}
// clean the nodes
Vec_PtrForEachEntryStart( vFrontier, pObj, k, i )
pObj->fMarkA = 0;
// report the results
if ( RetValue == ABC_UPDATE_FAIL )
printf( "Period = %3d. Updated nodes = %6d. Infeasible\n", Fi, vFrontier->nSize );
else
printf( "Period = %3d. Updated nodes = %6d. Feasible\n", Fi, vFrontier->nSize );
Vec_PtrFree( vFrontier );
return RetValue != ABC_UPDATE_FAIL;
}
/**Function*************************************************************
Synopsis [Computes the l-value of the node.]
Description []
SideEffects []
SeeAlso []
***********************************************************************/
int Abc_NodeUpdateLValue( Abc_Obj_t * pObj, int Fi )
{
int lValueNew, lValue0, lValue1;
assert( !Abc_ObjIsPi(pObj) );
lValue0 = Abc_NodeReadLValue(Abc_ObjFanin0(pObj)) - Fi * Abc_ObjFaninL0(pObj);
if ( Abc_ObjFaninNum(pObj) == 2 )
lValue1 = Abc_NodeReadLValue(Abc_ObjFanin1(pObj)) - Fi * Abc_ObjFaninL1(pObj);
else
lValue1 = -ABC_INFINITY;
lValueNew = 1 + ABC_MAX( lValue0, lValue1 );
if ( Abc_ObjIsPo(pObj) && lValueNew > Fi )
return ABC_UPDATE_FAIL;
if ( lValueNew == Abc_NodeReadLValue(pObj) )
return ABC_UPDATE_NO;
Abc_NodeSetLValue( pObj, lValueNew );
return ABC_UPDATE_YES;
}
////////////////////////////////////////////////////////////////////////
/// END OF FILE ///
////////////////////////////////////////////////////////////////////////
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