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/*
* Copyright (c) 2000 Stephen Williams (steve@icarus.com)
*
* This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU
* General Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#ifdef HAVE_CVS_IDENT
#ident "$Id: link_const.cc,v 1.15 2002/08/12 01:34:59 steve Exp $"
#endif

# include "config.h"

# include "netlist.h"
# include "netmisc.h"

/*
* Scan the link for drivers. If there are only constant drivers, then
* the nexus has a known constant value. If there is a supply net,
* then the nexus again has a known constant value.
*/
bool Nexus::drivers_constant() const
{
      if (driven_ == VAR)
return false;
      if (driven_ != NO_GUESS)
return true;

      for (const Link*cur = list_ ; cur ; cur = cur->next_) {
const NetNet*sig;
Link::DIR cur_dir;

cur_dir = cur->get_dir();
if (cur_dir == Link::INPUT)
continue;

/* If this is an input or inout port of a root module,
then the is probably not a constant value. I
certainly don't know what the value is, anyhow. This
can happen in cases like this:

module main(sig);
input sig;
endmodule

If main is a root module (it has no parent) then sig
is not constant because it connects to an unspecified
outside world. */

if (cur_dir == Link::PASSIVE) {

const NetObj*obj = cur->get_obj();
if (obj->scope()->parent() != 0)
continue;

sig = dynamic_cast<const NetNet*>(cur->get_obj());
assert(sig);

if (sig->port_type() == NetNet::NOT_A_PORT)
continue;

if (sig->port_type() == NetNet::POUTPUT)
continue;

driven_ = VAR;
return false;

}

/* If there is a supply net, then this nexus will have a
constant value independent of any drivers. */
if (const NetNet*sig = dynamic_cast<const NetNet*>(cur->get_obj()))
switch (sig->type()) {
case NetNet::SUPPLY0:
driven_ = V0;
return true;
case NetNet::SUPPLY1:
driven_ = V1;
return true;
default:
break;
}

if (! dynamic_cast<const NetConst*>(cur->get_obj())) {
driven_ = VAR;
return false;
}
      }

      return true;
}

verinum::V Nexus::driven_value() const
{
      switch (driven_) {
case V0:
return verinum::V0;
case V1:
return verinum::V1;
case Vx:
return verinum::Vx;
case Vz:
return verinum::Vz;
case VAR:
assert(0);
break;
case NO_GUESS:
break;
      }

      const Link*cur = list_;

      verinum::V val = verinum::Vz;

      for (cur = list_ ; cur ; cur = cur->next_) {

const NetConst*obj;
const NetNet*sig;
if (obj = dynamic_cast<const NetConst*>(cur->get_obj())) {
val = obj->value(cur->get_pin());

} else if (sig = dynamic_cast<const NetNet*>(cur->get_obj())) {

if (sig->type() == NetNet::SUPPLY0) {
driven_ = V0;
return verinum::V0;
}
if (sig->type() == NetNet::SUPPLY1) {
driven_ = V1;
return verinum::V1;
}
}
      }

/* Cache the result. */
      switch (val) {
case verinum::V0:
driven_ = V0;
break;
case verinum::V1:
driven_ = V1;
break;
case verinum::Vx:
driven_ = Vx;
break;
case verinum::Vz:
driven_ = Vz;
break;
      }

      return val;
}

/*
* $Log: link_const.cc,v $
* Revision 1.15 2002/08/12 01:34:59 steve
* conditional ident string using autoconfig.
*
* Revision 1.14 2002/06/25 01:33:22 steve
* Cache calculated driven value.
*
* Revision 1.13 2002/06/24 01:49:39 steve
* Make link_drive_constant cache its results in
* the Nexus, to improve cprop performance.
*
* Revision 1.12 2002/06/19 04:18:46 steve
* Shuffle link_drivers_constant for speed.
*
* Revision 1.11 2001/08/25 23:50:03 steve
* Change the NetAssign_ class to refer to the signal
* instead of link into the netlist. This is faster
* and uses less space. Make the NetAssignNB carry
* the delays instead of the NetAssign_ lval objects.
*
* Change the vvp code generator to support multiple
* l-values, i.e. concatenations of part selects.
*
* Revision 1.10 2001/07/25 03:10:49 steve
* Create a config.h.in file to hold all the config
* junk, and support gcc 3.0. (Stephan Boettcher)
*
* Revision 1.9 2001/07/07 03:01:37 steve
* Detect and make available to t-dll the right shift.
*
* Revision 1.8 2001/02/16 03:27:07 steve
* links to root inputs are not constant.
*
* Revision 1.7 2000/11/20 01:41:12 steve
* Whoops, return the calculated constant value rom driven_value.
*
* Revision 1.6 2000/11/20 00:58:40 steve
* Add support for supply nets (PR#17)
*
* Revision 1.5 2000/07/14 06:12:57 steve
* Move inital value handling from NetNet to Nexus
* objects. This allows better propogation of inital
* values.
*
* Clean up constant propagation a bit to account
* for regs that are not really values.
*
* Revision 1.4 2000/06/25 19:59:42 steve
* Redesign Links to include the Nexus class that
* carries properties of the connected set of links.
*
* Revision 1.3 2000/05/14 17:55:04 steve
* Support initialization of FF Q value.
*
* Revision 1.2 2000/05/07 04:37:56 steve
* Carry strength values from Verilog source to the
* pform and netlist for gates.
*
* Change vvm constants to use the driver_t to drive
* a constant value. This works better if there are
* multiple drivers on a signal.
*
* Revision 1.1 2000/04/20 00:28:03 steve
* Catch some simple identity compareoptimizations.
*
*/

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