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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
*/

# 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 = first_nlink() ; cur ; cur = cur->next_nlink()) {
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 NetPins*obj = cur->get_obj();
const NetObj*as_obj = dynamic_cast<const NetObj*>(obj);
if (as_obj == 0 || as_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*s = dynamic_cast<const NetNet*>(cur->get_obj()))
switch (s->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 = first_nlink() ; cur ; cur = cur->next_nlink()) {

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 we find an attached SUPPLY0/1, the we know
// from that what the driven value is. Stop now.
if (sig->type() == NetNet::SUPPLY0) {
driven_ = V0;
return verinum::V0;
}
if (sig->type() == NetNet::SUPPLY1) {
driven_ = V1;
return verinum::V1;
}

// If we find an attached TRI0/1, then this is a
// good guess for the driven value, but keep
// looking for something better.
if (sig->type() == NetNet::TRI0) {
val = verinum::V0;
}
if (sig->type() == NetNet::TRI1) {
val = 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;
}

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