elaborate.cc

/*
 * Copyright (c) 1998-2000 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
 */
#if !defined(WINNT) && !defined(macintosh)
#ident "$Id: elaborate.cc,v 1.254 2002/06/19 04:20:03 steve Exp $"
#endif

# include "config.h"

/*
 * Elaboration takes as input a complete parse tree and the name of a
 * root module, and generates as output the elaborated design. This
 * elaborated design is presented as a Module, which does not
 * reference any other modules. It is entirely self contained.
 */

# include  <typeinfo>
# include  <strstream>
# include  <list>
# include  "pform.h"
# include  "PEvent.h"
# include  "netlist.h"
# include  "netmisc.h"
# include  "util.h"
# include  "parse_api.h"
# include  "compiler.h"


static Link::strength_t drive_type(PGate::strength_t drv)
{
      switch (drv) {
	  case PGate::HIGHZ:
	    return Link::HIGHZ;
	  case PGate::WEAK:
	    return Link::WEAK;
	  case PGate::PULL:
	    return Link::PULL;
	  case PGate::STRONG:
	    return Link::STRONG;
	  case PGate::SUPPLY:
	    return Link::SUPPLY;
	  default:
	    assert(0);
      }
      return Link::STRONG;
}


void PGate::elaborate(Design*des, NetScope*scope) const
{
      cerr << "internal error: what kind of gate? " <<
	    typeid(*this).name() << endl;
}

/*
 * Elaborate the continuous assign. (This is *not* the procedural
 * assign.) Elaborate the lvalue and rvalue, and do the assignment.
 */
void PGAssign::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      unsigned long rise_time, fall_time, decay_time;
      eval_delays(des, scope, rise_time, fall_time, decay_time);

      Link::strength_t drive0 = drive_type(strength0());
      Link::strength_t drive1 = drive_type(strength1());

      assert(pin(0));
      assert(pin(1));

	/* Elaborate the l-value. */
      NetNet*lval = pin(0)->elaborate_lnet(des, scope);
      if (lval == 0) {
	    des->errors += 1;
	    return;
      }


	/* Handle the special case that the rval is simply an
	   identifier. Get the rval as a NetNet, then use NetBUFZ
	   objects to connect it to the l-value. This is necessary to
	   direct drivers. This is how I attach strengths to the
	   assignment operation. */
      if (const PEIdent*id = dynamic_cast<const PEIdent*>(pin(1))) {
	    NetNet*rid = id->elaborate_net(des, scope, lval->pin_count(),
					   0, 0, 0, Link::STRONG,
					   Link::STRONG);
	    if (rid == 0) {
		  des->errors += 1;
		  return;
	    }

	    assert(rid);


	      /* If the right hand net is the same type as the left
		 side net (i.e. WIRE/WIRE) then it is enough to just
		 connect them together. Otherwise, put a bufz between
		 them to carry strengths from the rval.

		 While we are at it, handle the case where the r-value
		 is not as wide as th l-value by padding with a
		 constant-0. */

	    unsigned cnt = lval->pin_count();
	    if (rid->pin_count() < cnt)
		  cnt = rid->pin_count();

	    if ((rid->type() == lval->type()) && (rise_time == 0)) {
		  unsigned idx;
		  for (idx = 0 ;  idx < cnt; idx += 1)
			connect(lval->pin(idx), rid->pin(idx));

		  if (cnt < lval->pin_count()) {
			verinum tmpv (0UL, lval->pin_count()-cnt);
			NetConst*tmp = new NetConst(scope,
						    scope->local_hsymbol(),
						    tmpv);
			des->add_node(tmp);
			for (idx = cnt ;  idx < lval->pin_count() ; idx += 1)
			      connect(lval->pin(idx), tmp->pin(idx-cnt));
		  }

	    } else {
		  unsigned idx;
		  for (idx = 0 ; idx < cnt ;  idx += 1) {
			NetBUFZ*dev = new NetBUFZ(scope,
						  scope->local_hsymbol());
			connect(lval->pin(idx), dev->pin(0));
			connect(rid->pin(idx), dev->pin(1));
			dev->rise_time(rise_time);
			dev->fall_time(fall_time);
			dev->decay_time(decay_time);
			dev->pin(0).drive0(drive0);
			dev->pin(0).drive1(drive1);
			des->add_node(dev);
		  }

		  if (cnt < lval->pin_count()) {
			NetConst*dev = new NetConst(scope,
						    scope->local_hsymbol(),
						    verinum::V0);
			
			des->add_node(dev);
			dev->pin(0).drive0(drive0);
			dev->pin(0).drive1(drive1);
			for (idx = cnt ;  idx < lval->pin_count() ; idx += 1)
			      connect(lval->pin(idx), dev->pin(0));
		  }
	    }

	    return;
      }

	/* Elaborate the r-value. Account for the initial decays,
	   which are going to be attached to the last gate before the
	   generated NetNet. */
      NetNet*rval = pin(1)->elaborate_net(des, scope,
					  lval->pin_count(),
					  rise_time, fall_time, decay_time,
					  drive0, drive1);
      if (rval == 0) {
	    cerr << get_line() << ": error: Unable to elaborate r-value: "
		 << *pin(1) << endl;
	    des->errors += 1;
	    return;
      }

      assert(lval && rval);


	/* If the r-value insists on being smaller then the l-value
	   (perhaps it is explicitly sized) the pad it out to be the
	   right width so that something is connected to all the bits
	   of the l-value. */
      if (lval->pin_count() > rval->pin_count())
	    rval = pad_to_width(des, rval, lval->pin_count());

      for (unsigned idx = 0 ;  idx < lval->pin_count() ;  idx += 1)
	    connect(lval->pin(idx), rval->pin(idx));

      if (lval->local_flag())
	    delete lval;

}

/*
 * Elaborate a Builtin gate. These normally get translated into
 * NetLogic nodes that reflect the particular logic function.
 */
void PGBuiltin::elaborate(Design*des, NetScope*scope) const
{
      unsigned count = 1;
      unsigned low = 0, high = 0;
      string name = get_name();

      if (name == "")
	    name = scope->local_hsymbol();
      else
	    name = scope->name()+"."+name;

	/* If the verilog source has a range specification for the
	   gates, then I am expected to make more then one
	   gate. Figure out how many are desired. */
      if (msb_) {
	    verinum*msb = msb_->eval_const(des, scope);
	    verinum*lsb = lsb_->eval_const(des, scope);

	    if (msb == 0) {
		  cerr << get_line() << ": error: Unable to evaluate "
			"expression " << *msb_ << endl;
		  des->errors += 1;
		  return;
	    }

	    if (lsb == 0) {
		  cerr << get_line() << ": error: Unable to evaluate "
			"expression " << *lsb_ << endl;
		  des->errors += 1;
		  return;
	    }

	    if (msb->as_long() > lsb->as_long())
		  count = msb->as_long() - lsb->as_long() + 1;
	    else
		  count = lsb->as_long() - msb->as_long() + 1;

	    low = lsb->as_long();
	    high = msb->as_long();
      }


	/* Allocate all the getlist nodes for the gates. */
      NetLogic**cur = new NetLogic*[count];
      assert(cur);

	/* Calculate the gate delays from the delay expressions
	   given in the source. For logic gates, the decay time
	   is meaningless because it can never go to high
	   impedence. However, the bufif devices can generate
	   'bz output, so we will pretend that anything can.

	   If only one delay value expression is given (i.e. #5
	   nand(foo,...)) then rise, fall and decay times are
	   all the same value. If two values are given, rise and
	   fall times are use, and the decay time is the minimum
	   of the rise and fall times. Finally, if all three
	   values are given, they are taken as specified. */

      unsigned long rise_time, fall_time, decay_time;
      eval_delays(des, scope, rise_time, fall_time, decay_time);

      struct attrib_list_t*attrib_list = 0;
      unsigned attrib_list_n = 0;
      attrib_list = evaluate_attributes(attributes, attrib_list_n,
					des, scope);

	/* Now make as many gates as the bit count dictates. Give each
	   a unique name, and set the delay times. */

      for (unsigned idx = 0 ;  idx < count ;  idx += 1) {
	    strstream tmp;
	    unsigned index;
	    if (low < high)
		  index = low + idx;
	    else
		  index = low - idx;

	    tmp << name << "<" << index << ">" << ends;
	    const string inm = tmp.str();

	    switch (type()) {
		case AND:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::AND);
		  break;
		case BUF:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::BUF);
		  break;
		case BUFIF0:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::BUFIF0);
		  break;
		case BUFIF1:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::BUFIF1);
		  break;
		case NAND:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NAND);
		  break;
		case NMOS:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NMOS);
		  break;
		case NOR:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NOR);
		  break;
		case NOT:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NOT);
		  break;
		case NOTIF0:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NOTIF0);
		  break;
		case NOTIF1:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::NOTIF1);
		  break;
		case OR:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::OR);
		  break;
		case RNMOS:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::RNMOS);
		  break;
		case RPMOS:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::RPMOS);
		  break;
		case PMOS:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::PMOS);
		  break;
		case PULLDOWN:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::PULLDOWN);
		  break;
		case PULLUP:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::PULLUP);
		  break;
		case XNOR:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::XNOR);
		  break;
		case XOR:
		  cur[idx] = new NetLogic(scope, inm, pin_count(),
					  NetLogic::XOR);
		  break;
		default:
		  cerr << get_line() << ": internal error: unhandled "
			"gate type." << endl;
		  des->errors += 1;
		  return;
	    }

	    for (unsigned adx = 0 ;  adx < attrib_list_n ;  adx += 1)
		  cur[idx]->attribute(attrib_list[adx].key,
				      attrib_list[adx].val);

	    cur[idx]->rise_time(rise_time);
	    cur[idx]->fall_time(fall_time);
	    cur[idx]->decay_time(decay_time);

	    cur[idx]->pin(0).drive0(drive_type(strength0()));
	    cur[idx]->pin(0).drive1(drive_type(strength1()));

	    des->add_node(cur[idx]);
      }


      delete[]attrib_list;

	/* The gates have all been allocated, this loop runs through
	   the parameters and attaches the ports of the objects. */

      for (unsigned idx = 0 ;  idx < pin_count() ;  idx += 1) {
	    const PExpr*ex = pin(idx);
	    NetNet*sig = ex->elaborate_net(des, scope, 0, 0, 0, 0);
	    if (sig == 0)
		  continue;

	    assert(sig);

	    if (sig->pin_count() == 1)
		  for (unsigned gdx = 0 ;  gdx < count ;  gdx += 1)
			connect(cur[gdx]->pin(idx), sig->pin(0));

	    else if (sig->pin_count() == count)
		  for (unsigned gdx = 0 ;  gdx < count ;  gdx += 1)
			connect(cur[gdx]->pin(idx), sig->pin(gdx));

	    else {
		  cerr << get_line() << ": error: Gate count of " <<
			count << " does not match net width of " <<
			sig->pin_count() << " at pin " << idx << "."
		       << endl;
		  des->errors += 1;
	    }

	    if (NetSubnet*tmp = dynamic_cast<NetSubnet*>(sig))
		  delete tmp;
      }
}

/*
 * Instantiate a module by recursively elaborating it. Set the path of
 * the recursive elaboration so that signal names get properly
 * set. Connect the ports of the instantiated module to the signals of
 * the parameters. This is done with BUFZ gates so that they look just
 * like continuous assignment connections.
 */
void PGModule::elaborate_mod_(Design*des, Module*rmod, NetScope*scope) const
{
	// Missing module instance names have already been rejected.
      assert(get_name() != "");

      if (msb_) {
	    cerr << get_line() << ": sorry: Module instantiation arrays "
		  "are not yet supported." << endl;
	    des->errors += 1;
	    return;
      }

      assert(scope);

	// I know a priori that the elaborate_scope created the scope
	// already, so just look it up as a child of the current scope.
      NetScope*my_scope = scope->child(get_name());
      assert(my_scope);

      const svector<PExpr*>*pins;

	// Detect binding by name. If I am binding by name, then make
	// up a pins array that reflects the positions of the named
	// ports. If this is simply positional binding in the first
	// place, then get the binding from the base class.
      if (pins_) {
	    unsigned nexp = rmod->port_count();
	    svector<PExpr*>*exp = new svector<PExpr*>(nexp);

	      // Scan the bindings, matching them with port names.
	    for (unsigned idx = 0 ;  idx < npins_ ;  idx += 1) {

		    // Given a binding, look at the module port names
		    // for the position that matches the binding name.
		  unsigned pidx = rmod->find_port(pins_[idx].name);

		    // If the port name doesn't exist, the find_port
		    // method will return the port count. Detect that
		    // as an error.
		  if (pidx == nexp) {
			cerr << get_line() << ": error: port ``" <<
			      pins_[idx].name << "'' is not a port of "
			     << get_name() << "." << endl;
			des->errors += 1;
			continue;
		  }

		    // If I already bound something to this port, then
		    // the (*exp) array will already have a pointer
		    // value where I want to place this expression.
		  if ((*exp)[pidx]) {
			cerr << get_line() << ": error: port ``" <<
			      pins_[idx].name << "'' already bound." <<
			      endl;
			des->errors += 1;
			continue;
		  }

		    // OK, do the binding by placing the expression in
		    // the right place.
		  (*exp)[pidx] = pins_[idx].parm;
	    }

	    pins = exp;

      } else if (pin_count() == 0) {

	      /* Handle the special case that no ports are
		 connected. It is possible that this is an empty
		 connect-by-name list, su we'll allow it and assume
		 that is the case. */

	    svector<PExpr*>*tmp = new svector<PExpr*>(rmod->port_count());
	    for (unsigned idx = 0 ;  idx < rmod->port_count() ;  idx += 1)
		  (*tmp)[idx] = 0;

	    pins = tmp;

      } else {

	      /* Otherwise, this is a positional list of fort
		 connections. In this case, the port count must be
		 right. Check that is is, the get the pin list. */

	    if (pin_count() != rmod->port_count()) {
		  cerr << get_line() << ": error: Wrong number "
			"of ports. Expecting " << rmod->port_count() <<
			", got " << pin_count() << "."
		       << endl;
		  des->errors += 1;
		  return;
	    }

	      // No named bindings, just use the positional list I
	      // already have.
	    assert(pin_count() == rmod->port_count());
	    pins = get_pins();
      }

	// Elaborate this instance of the module. The recursive
	// elaboration causes the module to generate a netlist with
	// the ports represented by NetNet objects. I will find them
	// later.
      rmod->elaborate(des, my_scope);

	// Now connect the ports of the newly elaborated designs to
	// the expressions that are the instantiation parameters. Scan
	// the pins, elaborate the expressions attached to them, and
	// bind them to the port of the elaborated module.

	// This can get rather complicated because the port can be
	// unconnected (meaning an empty paramter is passed) connected
	// to a concatenation, or connected to an internally
	// unconnected port.

      for (unsigned idx = 0 ;  idx < pins->count() ;  idx += 1) {

	      // Skip unconnected module ports. This happens when a
	      // null parameter is passed in.
	    if ((*pins)[idx] == 0)
		  continue;

	      // Inside the module, the port is zero or more signals
	      // that were already elaborated. List all those signals
	      // and the NetNet equivilents.
	    svector<PEIdent*> mport = rmod->get_port(idx);
	    svector<NetNet*>prts (mport.count());

	      // Count the internal pins of the port.
	    unsigned prts_pin_count = 0;
	    for (unsigned ldx = 0 ;  ldx < mport.count() ;  ldx += 1) {
		  PEIdent*pport = mport[ldx];
		  assert(pport);
		  prts[ldx] = pport->elaborate_port(des, my_scope);
		  if (prts[ldx] == 0)
			continue;

		  assert(prts[ldx]);
		  prts_pin_count += prts[ldx]->pin_count();
	    }

	      // If I find that the port in unconnected inside the
	      // module, then there is nothing to connect. Skip the
	      // paramter.
	    if (prts_pin_count == 0) {
		  continue;
	    }

	      // Elaborate the expression that connects to the module
	      // port. sig is the thing outside the module that
	      // connects to the port.

	    NetNet*sig = (*pins)[idx]->elaborate_net(des, scope,
						     prts_pin_count,
						     0, 0, 0);
	    if (sig == 0) {
		  cerr << "internal error: Expression too complicated "
			"for elaboration." << endl;
		  continue;
	    }

	    assert(sig);

	      // Check that a reg is not passed as an output or inout
	      // port of the module. sig is the elaborated signal in
	      // the outside that is to be passed, and prts is a
	      // concatenation of signals on the input that receive a
	      // reg value.
	    if ((sig->type() == NetNet::REG)
		&& (prts.count() >= 1)
		&& (prts[0]->port_type() != NetNet::PINPUT)) {
		  cerr << get_line() << ": error: reg/variable "
		       << sig->name() << " cannot connect to "
		       << "output port " << (idx+1) << " of "
		       << my_scope->name() << "." << endl;
		  des->errors += 1;
		  continue;
	    }


	      // Check that the parts have matching pin counts. If
	      // not, they are different widths. Note that idx is 0
	      // based, but users count parameter positions from 1.
	    if (prts_pin_count != sig->pin_count()) {
		  cerr << get_line() << ": warning: Port " << (idx+1) << " of "
		       << type_ << " expects " << prts_pin_count <<
			" pins, got " << sig->pin_count() << "." << endl;

		  if (prts_pin_count > sig->pin_count()) {
			cerr << get_line() << ":        : Leaving "
			     << (prts_pin_count-sig->pin_count())
			     << " high bits of the port unconnected."
			     << endl;
		  } else {
			cerr << get_line() << ":        : Leaving "
			     << (sig->pin_count()-prts_pin_count)
			     << " high bits of the parameter dangling."
			     << endl;
		  }
	    }

	      // Connect the sig expression that is the context of the
	      // module instance to the ports of the elaborated module.

	      // The prts_pin_count variable is the total width of the
	      // port and is the maximum number of connections to
	      // make. sig is the elaborated expression that connects
	      // to that port. If sig has too few pins, then reduce
	      // the number of connections to make.

	      // Connect this many of the port pins. If the expression
	      // is too small, the reduce the number of connects.
	    unsigned ccount = prts_pin_count;
	    if (sig->pin_count() < ccount)
		  ccount = sig->pin_count();

	      // Now scan the concatenation that makes up the port,
	      // connecting pins until we run out of port pins or sig
	      // pins.

	    unsigned spin = 0;
	    for (unsigned ldx = prts.count() ;  ldx > 0 ;  ldx -= 1) {
		  unsigned cnt = prts[ldx-1]->pin_count();
		  if (cnt > ccount)
			cnt = ccount;
		  for (unsigned p = 0 ;  p < cnt ;  p += 1) {
			connect(sig->pin(spin), prts[ldx-1]->pin(p));
			ccount -= 1;
			spin += 1;
		  }
		  if (ccount == 0)
			break;
	    }


	    if (NetSubnet*tmp = dynamic_cast<NetSubnet*>(sig))
		  delete tmp;
      }
}

/*
 * From a UDP definition in the source, make a NetUDP
 * object. Elaborate the pin expressions as netlists, then connect
 * those networks to the pins.
 */

void PGModule::elaborate_udp_(Design*des, PUdp*udp, NetScope*scope) const
{

      string my_name = get_name();
      if (my_name == "")
	    my_name = scope->local_hsymbol();
      else
	    my_name = scope->name()+"."+my_name;

	/* When the parser notices delay expressions in front of a
	   module or primitive, it interprets them as parameter
	   overrides. Correct that misconception here. */
      unsigned long rise_time = 0, fall_time = 0, decay_time = 0;
      if (overrides_) {
	    PDelays tmp_del;
	    tmp_del.set_delays(overrides_, false);
	    tmp_del.eval_delays(des, scope, rise_time, fall_time, decay_time);
      }


      NetUDP*net = new NetUDP(scope, my_name, udp->ports.count(), udp);
      net->rise_time(rise_time);
      net->fall_time(fall_time);
      net->decay_time(decay_time);

      struct attrib_list_t*attrib_list = 0;
      unsigned attrib_list_n = 0;
      attrib_list = evaluate_attributes(attributes, attrib_list_n,
					des, scope);

      for (unsigned adx = 0 ;  adx < attrib_list_n ;  adx += 1)
	    net->attribute(attrib_list[adx].key, attrib_list[adx].val);

      delete[]attrib_list;

	/* Run through the pins, making netlists for the pin
	   expressions and connecting them to the pin in question. All
	   of this is independent of the nature of the UDP. */
      for (unsigned idx = 0 ;  idx < net->pin_count() ;  idx += 1) {
	    if (pin(idx) == 0)
		  continue;

	    NetNet*sig = pin(idx)->elaborate_net(des, scope, 1, 0, 0, 0);
	    if (sig == 0) {
		  cerr << "internal error: Expression too complicated "
			"for elaboration:" << *pin(idx) << endl;
		  continue;
	    }

	    connect(sig->pin(0), net->pin(idx));

	      // Delete excess holding signal.
	    if (NetSubnet*tmp = dynamic_cast<NetSubnet*>(sig))
		  delete tmp;
      }
      
	// All done. Add the object to the design.
      des->add_node(net);
}


bool PGModule::elaborate_sig(Design*des, NetScope*scope) const
{
	// Look for the module type
      map<string,Module*>::const_iterator mod = pform_modules.find(type_);
      if (mod != pform_modules.end())
	    return elaborate_sig_mod_(des, scope, (*mod).second);

      return true;
}


void PGModule::elaborate(Design*des, NetScope*scope) const
{
	// Look for the module type
      map<string,Module*>::const_iterator mod = pform_modules.find(type_);
      if (mod != pform_modules.end()) {
	    elaborate_mod_(des, (*mod).second, scope);
	    return;
      }

	// Try a primitive type
      map<string,PUdp*>::const_iterator udp = pform_primitives.find(type_);
      if (udp != pform_primitives.end()) {
	    elaborate_udp_(des, (*udp).second, scope);
	    return;
      }

      cerr << get_line() << ": internal error: Unknown module type: " <<
	    type_ << endl;
}

void PGModule::elaborate_scope(Design*des, NetScope*sc) const
{
	// Look for the module type
      map<string,Module*>::const_iterator mod = pform_modules.find(type_);
      if (mod != pform_modules.end()) {
	    elaborate_scope_mod_(des, (*mod).second, sc);
	    return;
      }

	// Try a primitive type
      map<string,PUdp*>::const_iterator udp = pform_primitives.find(type_);
      if (udp != pform_primitives.end())
	    return;

	// Not a module or primitive that I know about yet, so try to
	// load a library module file (which parses some new Verilog
	// code) and try again.
      if (load_module(type_)) {

	      // Try again to find the module type
	    mod = pform_modules.find(type_);
	    if (mod != pform_modules.end()) {
		  elaborate_scope_mod_(des, (*mod).second, sc);
		  return;
	    }

	      // Try again to find a primitive type
	    udp = pform_primitives.find(type_);
	    if (udp != pform_primitives.end())
		  return;
      }


	// Not a module or primitive that I know about or can find by
	// any means, so give up.
      cerr << get_line() << ": error: Unknown module type: " << type_ << endl;
      des->errors += 1;
}

/*
 * The concatenation is also OK an an l-value. This method elaborates
 * it as a structural l-value.
 */
NetNet* PEConcat::elaborate_lnet(Design*des, NetScope*scope) const
{
      assert(scope);

      svector<NetNet*>nets (parms_.count());
      unsigned pins = 0;
      unsigned errors = 0;

      if (repeat_) {
	    cerr << get_line() << ": sorry: I do not know how to"
		  " elaborate repeat concatenation nets." << endl;
	    return 0;
      }

	/* Elaborate the operands of the concatenation. */
      for (unsigned idx = 0 ;  idx < nets.count() ;  idx += 1) {
	    nets[idx] = parms_[idx]->elaborate_lnet(des, scope);
	    if (nets[idx] == 0)
		  errors += 1;
	    else
		  pins += nets[idx]->pin_count();
      }

	/* If any of the sub expressions failed to elaborate, then
	   delete all those that did and abort myself. */
      if (errors) {
	    for (unsigned idx = 0 ;  idx < nets.count() ;  idx += 1) {
		  if (nets[idx]) delete nets[idx];
	    }
	    des->errors += 1;
	    return 0;
      }

	/* Make the temporary signal that connects to all the
	   operands, and connect it up. Scan the operands of the
	   concat operator from least significant to most significant,
	   which is opposite from how they are given in the list. */
      NetNet*osig = new NetNet(scope, des->local_symbol(scope->name()),
			       NetNet::IMPLICIT, pins);
      pins = 0;
      for (unsigned idx = nets.count() ;  idx > 0 ;  idx -= 1) {
	    NetNet*cur = nets[idx-1];
	    for (unsigned pin = 0 ;  pin < cur->pin_count() ;  pin += 1) {
		  connect(osig->pin(pins), cur->pin(pin));
		  pins += 1;
	    }
      }

      osig->local_flag(true);
      return osig;
}

NetProc* Statement::elaborate(Design*des, NetScope*) const
{
      cerr << get_line() << ": internal error: elaborate: "
	    "What kind of statement? " << typeid(*this).name() << endl;
      NetProc*cur = new NetProc;
      des->errors += 1;
      return cur;
}


NetAssign_* PAssign_::elaborate_lval(Design*des, NetScope*scope) const
{
      assert(lval_);
      return lval_->elaborate_lval(des, scope);
}

/*
 * This function elaborates delay expressions. This is a little
 * different from normal elaboration because the result may need to be
 * scaled.
 */
static NetExpr*elaborate_delay_expr(PExpr*expr, Design*des, NetScope*scope)
{

      if (verireal*dr = expr->eval_rconst(des, scope)) {
	    int shift = scope->time_unit() - des->get_precision();
	    long val = dr->as_long(shift);
	    delete dr;
	    return new NetEConst(verinum(val));

      }

      if (verinum*dv = expr->eval_const(des, scope)) {
	    unsigned long val = dv->as_ulong();
	    val = des->scale_to_precision(val, scope);
	    return new NetEConst(verinum(val));

      }

      NetExpr*delay = expr->elaborate_expr(des, scope);

      int shift = scope->time_unit() - des->get_precision();
      if (shift > 0) {
	    unsigned long scale = 1;
	    while (shift > 0) {
		  scale *= 10;
		  shift -= 1;
	    }

	    NetExpr*scal_val = new NetEConst(verinum(scale));
	    delay = new NetEBMult('*', delay, scal_val);
      }

      if (shift < 0) {
	    unsigned long scale = 1;
	    while (shift < 0) {
		  scale *= 10;
		  shift += 1;
	    }

	    NetExpr*scal_val = new NetEConst(verinum(scale));
	    delay = new NetEBDiv('/', delay, scal_val);
      }

      return delay;
}

NetProc* PAssign::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

	/* elaborate the lval. This detects any part selects and mux
	   expressions that might exist. */
      NetAssign_*lv = elaborate_lval(des, scope);
      if (lv == 0) return 0;

	/* If there is an internal delay expression, elaborate it. */
      NetExpr*delay = 0;
      if (delay_ != 0)
	    delay = elaborate_delay_expr(delay_, des, scope);


	/* Elaborate the r-value expression. */
      assert(rval());

      NetExpr*rv;

      if (verinum*val = rval()->eval_const(des, scope)) {
	    rv = new NetEConst(*val);
	    delete val;

      } else if (rv = rval()->elaborate_expr(des, scope)) {

	      /* OK, go on. */

      } else {
	      /* Unable to elaborate expression. Retreat. */
	    return 0;
      }

      assert(rv);

	/* Try to evaluate the expression, at least as far as possible. */
      if (NetExpr*tmp = rv->eval_tree()) {
	    delete rv;
	    rv = tmp;
      }

	/* Rewrite delayed assignments as assignments that are
	   delayed. For example, a = #<d> b; becomes:

	     begin
	        tmp = b;
		#<d> a = tmp;
	     end

	   If the delay is an event delay, then the transform is
	   similar, with the event delay replacing the time delay. It
	   is an event delay if the event_ member has a value.

	   This rewriting of the expression allows me to not bother to
	   actually and literally represent the delayed assign in the
	   netlist. The compound statement is exactly equivalent. */

      if (delay || event_) {
	    string n = scope->local_hsymbol();
	    unsigned wid = lv->lwidth();

	    rv->set_width(wid);
	    rv = pad_to_width(rv, wid);

	    if (! rv->set_width(wid)) {
		  cerr << get_line() << ": error: Unable to match "
			"expression width of " << rv->expr_width() <<
			" to l-value width of " << wid << "." << endl;
		    //XXXX delete rv;
		  return 0;
	    }

	    NetNet*tmp = new NetNet(scope, n, NetNet::REG, wid);
	    tmp->set_line(*this);

	    NetESignal*sig = new NetESignal(tmp);

	      /* Generate an assignment of the l-value to the temporary... */
	    n = scope->local_hsymbol();
	    NetAssign_*lvt = new NetAssign_(tmp);

	    NetAssign*a1 = new NetAssign(lvt, rv);
	    a1->set_line(*this);

	      /* Generate an assignment of the temporary to the r-value... */
	    NetAssign*a2 = new NetAssign(lv, sig);
	    a2->set_line(*this);

	      /* Generate the delay statement with the final
		 assignment attached to it. If this is an event delay,
		 elaborate the PEventStatement. Otherwise, create the
		 right NetPDelay object. */
	    NetProc*st;
	    if (event_) {
		  st = event_->elaborate_st(des, scope, a2);
		  if (st == 0) {
			cerr << event_->get_line() << ": error: "
			      "unable to elaborate event expression."
			     << endl;
			des->errors += 1;
			return 0;
		  }
		  assert(st);

	    } else {
		  NetPDelay*de = new NetPDelay(delay, a2);
		  st = de;
	    }

	      /* And build up the complex statement. */
	    NetBlock*bl = new NetBlock(NetBlock::SEQU, 0);
	    bl->append(a1);
	    bl->append(st);

	    return bl;
      }

      { unsigned wid = count_lval_width(lv);
        rv->set_width(wid);
	rv = pad_to_width(rv, wid);
	assert(rv->expr_width() >= wid);
      }

      NetAssign*cur = new NetAssign(lv, rv);
      cur->set_line(*this);

      return cur;
}

/*
 * The l-value of a procedural assignment is a very much constrained
 * expression. To wit, only identifiers, bit selects and part selects
 * are allowed. I therefore can elaborate the l-value by hand, without
 * the help of recursive elaboration.
 *
 * (For now, this does not yet support concatenation in the l-value.)
 */
NetProc* PAssignNB::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetAssign_*lv = elaborate_lval(des, scope);
      if (lv == 0) return 0;

      assert(rval());

	/* Elaborate the r-value expression. This generates a
	   procedural expression that I attach to the assignment. */
      NetExpr*rv = rval()->elaborate_expr(des, scope);
      if (rv == 0)
	    return 0;

      assert(rv);

      { unsigned wid = count_lval_width(lv);
        rv->set_width(wid);
	rv = pad_to_width(rv, wid);
      }

      NetExpr*delay = 0;
      if (delay_ != 0)
	    delay = elaborate_delay_expr(delay_, des, scope);

	/* All done with this node. mark its line number and check it in. */
      NetAssignNB*cur = new NetAssignNB(lv, rv);
      cur->set_delay(delay);
      cur->set_line(*this);
      return cur;
}


/*
 * This is the elaboration method for a begin-end block. Try to
 * elaborate the entire block, even if it fails somewhere. This way I
 * get all the error messages out of it. Then, if I detected a failure
 * then pass the failure up.
 */
NetProc* PBlock::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetBlock::Type type = (bl_type_==PBlock::BL_PAR)
	    ? NetBlock::PARA
	    : NetBlock::SEQU;

      NetScope*nscope = 0;
      if (name_.length()) {
	    nscope = scope->child(name_);
	    if (nscope == 0) {
		  cerr << get_line() << ": internal error: "
			"unable to find block scope " << scope->name()
		       << "<" << name_ << ">" << endl;
		  des->errors += 1;
		  return 0;
	    }

	    assert(nscope);

      }

      NetBlock*cur = new NetBlock(type, nscope);
      bool fail_flag = false;

      if (nscope == 0)
	    nscope = scope;

	// Handle the special case that the block contains only one
	// statement. There is no need to keep the block node.
      if (list_.count() == 1) {
	    assert(list_[0]);
	    NetProc*tmp = list_[0]->elaborate(des, nscope);
	    return tmp;
      }

      for (unsigned idx = 0 ;  idx < list_.count() ;  idx += 1) {
	    assert(list_[idx]);
	    NetProc*tmp = list_[idx]->elaborate(des, nscope);
	    if (tmp == 0) {
		  fail_flag = true;
		  continue;
	    }

	      // If the result turns out to be a noop, then skip it.
	    if (NetBlock*tbl = dynamic_cast<NetBlock*>(tmp))
		  if (tbl->proc_first() == 0) {
			delete tbl;
			continue;
		  }

	    cur->append(tmp);
      }

      if (fail_flag) {
	    delete cur;
	    cur = 0;
      }

      return cur;
}

/*
 * Elaborate a case statement.
 */
NetProc* PCase::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetExpr*expr = expr_->elaborate_expr(des, scope);
      if (expr == 0) {
	    cerr << get_line() << ": error: Unable to elaborate this case"
		  " expression." << endl;
	    return 0;
      }

	/* Try to evaluate the case expression. */
      if (! dynamic_cast<NetEConst*>(expr)) {
	    NetExpr*tmp = expr->eval_tree();
	    if (tmp != 0) {
		  delete expr;
		  expr = tmp;
	    }
      }

	/* Count the items in the case statement. Note that ther may
	   be some cases that have multiple guards. Count each as a
	   separate item. */
      unsigned icount = 0;
      for (unsigned idx = 0 ;  idx < items_->count() ;  idx += 1) {
	    PCase::Item*cur = (*items_)[idx];

	    if (cur->expr.count() == 0)
		  icount += 1;
	    else
		  icount += cur->expr.count();
      }

      NetCase*res = new NetCase(type_, expr, icount);
      res->set_line(*this);

	/* Iterate over all the case items (guard/statement pairs)
	   elaborating them. If the guard has no expression, then this
	   is a "default" cause. Otherwise, the guard has one or more
	   expressions, and each guard is a case. */
      unsigned inum = 0;
      for (unsigned idx = 0 ;  idx < items_->count() ;  idx += 1) {

	    assert(inum < icount);
	    PCase::Item*cur = (*items_)[idx];

	    if (cur->expr.count() == 0) {
		    /* If there are no expressions, then this is the
		       default case. */
		  NetProc*st = 0;
		  if (cur->stat)
			st = cur->stat->elaborate(des, scope);

		  res->set_case(inum, 0, st);
		  inum += 1;

	    } else for (unsigned e = 0; e < cur->expr.count(); e += 1) {

		    /* If there are one or more expressions, then
		       iterate over the guard expressions, elaborating
		       a separate case for each. (Yes, the statement
		       will be elaborated again for each.) */
		  NetExpr*gu = 0;
		  NetProc*st = 0;
		  assert(cur->expr[e]);
		  gu = cur->expr[e]->elaborate_expr(des, scope);

		    /* Try to evaluate the guard expression down to a
		       simple constant. */
		  if (! dynamic_cast<NetEConst*>(gu)) {
			NetExpr*tmp = gu->eval_tree();
			if (tmp != 0) {
			      delete gu;
			      gu = tmp;
			}
		  }

		  if (cur->stat)
			st = cur->stat->elaborate(des, scope);

		  res->set_case(inum, gu, st);
		  inum += 1;
	    }
      }

      return res;
}

NetProc* PCondit::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

	// Elaborate and try to evaluate the conditional expression.
      NetExpr*expr = expr_->elaborate_expr(des, scope);
      if (expr == 0) {
	    cerr << get_line() << ": error: Unable to elaborate"
		  " condition expression." << endl;
	    des->errors += 1;
	    return 0;
      }
      NetExpr*tmp = expr->eval_tree();
      if (tmp) {
	    delete expr;
	    expr = tmp;
      }

	// If the condition of the conditional statement is constant,
	// then look at the value and elaborate either the if statement
	// or the else statement. I don't need both. If there is no
	// else_ statement, the use an empty block as a noop.
      if (NetEConst*ce = dynamic_cast<NetEConst*>(expr)) {
	    verinum val = ce->value();
	    delete expr;
	    if (val[0] == verinum::V1)
		  return if_->elaborate(des, scope);
	    else if (else_)
		  return else_->elaborate(des, scope);
	    else
		  return new NetBlock(NetBlock::SEQU, 0);
      }

	// If the condition expression is more then 1 bits, then
	// generate a comparison operator to get the result down to
	// one bit. Turn <e> into <e> != 0;

      if (expr->expr_width() < 1) {
	    cerr << get_line() << ": internal error: "
		  "incomprehensible expression width (0)." << endl;
	    return 0;
      }

      if (expr->expr_width() > 1) {
	    assert(expr->expr_width() > 1);
	    verinum zero (verinum::V0, expr->expr_width());
	    NetEConst*ezero = new NetEConst(zero);
	    ezero->set_width(expr->expr_width());
	    NetEBComp*cmp = new NetEBComp('n', expr, ezero);
	    expr = cmp;
      }

	// Well, I actually need to generate code to handle the
	// conditional, so elaborate.
      NetProc*i = if_? if_->elaborate(des, scope) : 0;
      NetProc*e = else_? else_->elaborate(des, scope) : 0;

      NetCondit*res = new NetCondit(expr, i, e);
      res->set_line(*this);
      return res;
}

NetProc* PCallTask::elaborate(Design*des, NetScope*scope) const
{
      if (path_.peek_name(0)[0] == '$')
	    return elaborate_sys(des, scope);
      else
	    return elaborate_usr(des, scope);
}

/*
 * A call to a system task involves elaborating all the parameters,
 * then passing the list to the NetSTask object.
 *XXXX
 * There is a single special in the call to a system task. Normally,
 * an expression cannot take an unindexed memory. However, it is
 * possible to take a system task parameter a memory if the expression
 * is trivial.
 */
NetProc* PCallTask::elaborate_sys(Design*des, NetScope*scope) const
{
      assert(scope);

      svector<NetExpr*>eparms (nparms());

      for (unsigned idx = 0 ;  idx < nparms() ;  idx += 1) {
	    PExpr*ex = parm(idx);

	    eparms[idx] = ex? ex->elaborate_expr(des, scope, true) : 0;
      }

      NetSTask*cur = new NetSTask(path_.peek_name(0), eparms);
      return cur;
}

/*
 * A call to a user defined task is different from a call to a system
 * task because a user task in a netlist has no parameters: the
 * assignments are done by the calling thread. For example:
 *
 *  task foo;
 *    input a;
 *    output b;
 *    [...]
 *  endtask;
 *
 *  [...] foo(x, y);
 *
 * is really:
 *
 *  task foo;
 *    reg a;
 *    reg b;
 *    [...]
 *  endtask;
 *
 *  [...]
 *  begin
 *    a = x;
 *    foo;
 *    y = b;
 *  end
 */
NetProc* PCallTask::elaborate_usr(Design*des, NetScope*scope) const
{
      assert(scope);

      NetScope*task = des->find_task(scope, path_);
      if (task == 0) {
	    cerr << get_line() << ": error: Enable of unknown task "
		 << "``" << path_ << "''." << endl;
	    des->errors += 1;
	    return 0;
      }

      assert(task);
      assert(task->type() == NetScope::TASK);
      NetTaskDef*def = task->task_def();
      if (def == 0) {
	    cerr << get_line() << ": internal error: task " << path_
		 << " doesn't have a definition in " << scope->name()
		 << "." << endl;
	    des->errors += 1;
	    return 0;
      }
      assert(def);

      if (nparms() != def->port_count()) {
	    cerr << get_line() << ": error: Port count mismatch in call to ``"
		 << path_ << "''." << endl;
	    des->errors += 1;
	    return 0;
      }

      NetUTask*cur;

	/* Handle tasks with no parameters specially. There is no need
	   to make a sequential block to hold the generated code. */
      if (nparms() == 0) {
	    cur = new NetUTask(task);
	    return cur;
      }

      NetBlock*block = new NetBlock(NetBlock::SEQU, 0);


	/* Detect the case where the definition of the task is known
	   empty. In this case, we need not bother with calls to the
	   task, all the assignments, etc. Just return a no-op. */

      if (const NetBlock*tp = dynamic_cast<const NetBlock*>(def->proc())) {
	    if (tp->proc_first() == 0)
		  return block;
      }

	/* Generate assignment statement statements for the input and
	   INOUT ports of the task. These are managed by writing
	   assignments with the task port the l-value and the passed
	   expression the r-value. We know by definition that the port
	   is a reg type, so this elaboration is pretty obvious. */

      for (unsigned idx = 0 ;  idx < nparms() ;  idx += 1) {

	    NetNet*port = def->port(idx);
	    assert(port->port_type() != NetNet::NOT_A_PORT);
	    if (port->port_type() == NetNet::POUTPUT)
		  continue;

	    NetExpr*rv = parms_[idx]->elaborate_expr(des, scope);
	    NetAssign_*lv = new NetAssign_(port);
	    NetAssign*pr = new NetAssign(lv, rv);
	    block->append(pr);
      }

	/* Generate the task call proper... */
      cur = new NetUTask(task);
      block->append(cur);


	/* Generate assignment statements for the output and INOUT
	   ports of the task. The l-value in this case is the
	   expression passed as a parameter, and the r-value is the
	   port to be copied out.

	   We know by definition that the r-value of this copy-out is
	   the port, which is a reg. The l-value, however, may be any
	   expression that can be a target to a procedural
	   assignment, including a memory word. */

      for (unsigned idx = 0 ;  idx < nparms() ;  idx += 1) {

	    NetNet*port = def->port(idx);

	      /* Skip input ports. */
	    assert(port->port_type() != NetNet::NOT_A_PORT);
	    if (port->port_type() == NetNet::PINPUT)
		  continue;


	      /* Elaborate an l-value version of the port expression
		 for output and inout ports. If the expression does
		 not exist then quietly skip it, but if the expression
		 is not a valid l-value print an error message. Note
		 that the elaborate_lval method already printed a
		 detailed message. */
	    NetAssign_*lv;
	    if (parms_[idx]) {
		  lv = parms_[idx]->elaborate_lval(des, scope);
		  if (lv == 0) {
			cerr << parms_[idx]->get_line() << ": error: "
			     << "I give up on task port " << (idx+1)
			     << " expression: " << *parms_[idx] << endl;
		  }
	    } else {
		  lv = 0;
	    }

	    if (lv == 0)
		  continue;

	    NetESignal*sig = new NetESignal(port);

	      /* Generate the assignment statement. */
	    NetAssign*ass = new NetAssign(lv, sig);

	    block->append(ass);
      }

      return block;
}

NetCAssign* PCAssign::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetNet*lval = lval_->elaborate_anet(des, scope);
      if (lval == 0)
	    return 0;

      NetNet*rval = expr_->elaborate_net(des, scope, lval->pin_count(),
					 0, 0, 0);
      if (rval == 0)
	    return 0;

      if (rval->pin_count() < lval->pin_count())
	    rval = pad_to_width(des, rval, lval->pin_count());

      NetCAssign* dev = new NetCAssign(scope, scope->local_hsymbol(), lval);
      dev->set_line(*this);
      des->add_node(dev);

      for (unsigned idx = 0 ;  idx < dev->pin_count() ;  idx += 1)
	    connect(dev->pin(idx), rval->pin(idx));

      return dev;
}

NetDeassign* PDeassign::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetNet*lval = lval_->elaborate_anet(des, scope);
      if (lval == 0)
	    return 0;

      NetDeassign*dev = new NetDeassign(lval);
      dev->set_line( *this );
      return dev;
}

/*
 * Elaborate the delay statment (of the form #<expr> <statement>) as a
 * NetPDelay object. If the expression is constant, evaluate it now
 * and make a constant delay. If not, then pass an elaborated
 * expression to the constructor of NetPDelay so that the code
 * generator knows to evaluate the expression at run time.
 */
NetProc* PDelayStatement::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

	/* Catch the special case that the delay is given as a
	   floating point number. In this case, we need to scale the
	   delay to the units of the design. */

      if (verireal*fn = delay_? delay_->eval_rconst(des, scope) : 0) {
	    int shift = scope->time_unit() - des->get_precision();

	    long delay = fn->as_long(shift);
	    if (delay < 0)
		  delay = 0;

	    delete fn;

	    if (statement_)
		return new NetPDelay(delay, statement_->elaborate(des, scope));
	    else
		return new NetPDelay(delay, 0);

      }


      verinum*num = delay_->eval_const(des, scope);
      if (num == 0) {
	      /* Ah, the delay is not constant. OK, elaborate the
		 expression and let the run-time handle it. */
	    NetExpr*dex = delay_->elaborate_expr(des, scope);
	    if (statement_)
		  return new NetPDelay(dex, statement_->elaborate(des, scope));
	    else
		  return new NetPDelay(dex, 0);
      }
      assert(num);

	/* Convert the delay in the units of the scope to the
	   precision of the design as a whole. */
      unsigned long val = des->scale_to_precision(num->as_ulong(), scope);
      delete num;

	/* If there is a statement, then elaborate it and create a
	   NetPDelay statement to contain it. Note that we create a
	   NetPDelay statement even if the value is 0 because #0 does
	   in fact have a well defined meaning in Verilog. */

      if (statement_) {
	    NetProc*stmt = statement_->elaborate(des, scope);
	    return new NetPDelay(val, stmt);

      }  else {
	    return new NetPDelay(val, 0);
      }
}

/*
 * The disable statement is not yet supported.
 */
NetProc* PDisable::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetScope*target = des->find_scope(scope, scope_);
      if (target == 0) {
	    cerr << get_line() << ": error: Cannot find scope "
		 << scope_ << " in " << scope->name() << endl;
	    des->errors += 1;
	    return 0;
      }

      switch (target->type()) {
	  case NetScope::FUNC:
	    cerr << get_line() << ": error: Cannot disable functions." << endl;
	    des->errors += 1;
	    return 0;

	  case NetScope::MODULE:
	    cerr << get_line() << ": error: Cannot disable modules." << endl;
	    des->errors += 1;
	    return 0;

	  default:
	    break;
      }

      NetDisable*obj = new NetDisable(target);
      obj->set_line(*this);
      return obj;
}

/*
 * An event statement is an event delay of some sort, attached to a
 * statement. Some Verilog examples are:
 *
 *      @(posedge CLK) $display("clock rise");
 *      @event_1 $display("event triggered.");
 *      @(data or negedge clk) $display("data or clock fall.");
 *
 * The elaborated netlist uses the NetEvent, NetEvWait and NetEvProbe
 * classes. The NetEvWait class represents the part of the netlist
 * that is executed by behavioral code. The process starts waiting on
 * the NetEvent when it executes the NetEvWait step. Net NetEvProbe
 * and NetEvTrig are structural and behavioral equivilents that
 * trigger the event, and awakens any processes blocking in the
 * associated wait.
 *
 * The basic data structure is:
 *
 *       NetEvWait ---/--->  NetEvent  <----\---- NetEvProbe
 *        ...         |                     |         ...
 *       NetEvWait ---+                     +---- NetEvProbe
 *                                          |         ...
 *                                          +---- NetEvTrig
 *
 * That is, many NetEvWait statements may wait on a single NetEvent
 * object, and Many NetEvProbe objects may trigger the NetEvent
 * object. The many NetEvWait objects pointing to the NetEvent object
 * reflects the possibility of different places in the code blocking
 * on the same named event, like so:
 *
 *         event foo;
 *           [...]
 *         always begin @foo <statement1>; @foo <statement2> end
 *
 * This tends to not happen with signal edges. The multiple probes
 * pointing to the same event reflect the possibility of many
 * expressions in the same blocking statement, like so:
 *
 *         wire reset, clk;
 *           [...]
 *         always @(reset or posedge clk) <stmt>;
 *
 * Conjunctions like this cause a NetEvent object be created to
 * represent the overall conjuction, and NetEvProbe objects for each
 * event expression.
 *
 * If the NetEvent object represents a named event from the source,
 * then there are NetEvTrig objects that represent the trigger
 * statements instead of the NetEvProbe objects representing signals.
 * For example:
 *
 *         event foo;
 *         always @foo <stmt>;
 *         initial begin
 *                [...]
 *            -> foo;
 *                [...]
 *            -> foo;
 *                [...]
 *         end
 *
 * Each trigger statement in the source generates a separate NetEvTrig
 * object in the netlist. Those trigger objects are elaborated
 * elsewhere.
 *
 * Additional complications arise when named events show up in
 * conjunctions. An example of such a case is:
 *
 *         event foo;
 *         wire bar;
 *         always @(foo or posedge bar) <stmt>;
 *
 * Since there is by definition a NetEvent object for the foo object,
 * this is handled by allowing the NetEvWait object to point to
 * multiple NetEvent objects. All the NetEvProbe based objects are
 * collected and pointed as the synthetic NetEvent object, and all the
 * named events are added into the list of NetEvent object that the
 * NetEvWait object can refer to.
 */

NetProc* PEventStatement::elaborate_st(Design*des, NetScope*scope,
				       NetProc*enet) const
{
      assert(scope);


	/* The Verilog wait (<expr>) <statement> statement is a level
	   sensitive wait. Handle this special case by elaborating
	   something like this:

	       begin
	         if (! <expr>) @(posedge <expr>)
	         <statement>
	       end

	   This is equivilent, and uses the existing capapilities of
	   the netlist format. The resulting netlist should look like
	   this:

	       NetBlock ---+---> NetCondit --+--> <expr>
	                   |                 |
			   |     	     +--> NetEvWait--> NetEvent
			   |
			   +---> <statement>

	   This is quite a mouthful. Should I not move wait handling
	   to specialized objects? */


      if ((expr_.count() == 1) && (expr_[0]->type() == PEEvent::POSITIVE)) {

	    bool save_flag = error_implicit;
	    error_implicit = true;
	    NetNet*ex = expr_[0]->expr()->elaborate_net(des, scope,
							1, 0, 0, 0);
	    error_implicit = save_flag;

	    if (ex == 0) {
		  expr_[0]->dump(cerr);
		  cerr << endl;
		  des->errors += 1;
		  return 0;
	    }

	      /* Create a NetEvent object to manage this event. Note
		 that the NetEvent object's name has no hierarchy. */
	    NetEvent*ev = new NetEvent(scope->local_symbol());
	    scope->add_event(ev);

	    NetEvWait*we = new NetEvWait(0);
	    we->add_event(ev);

	    NetEvProbe*po = new NetEvProbe(scope,
					   scope->local_hsymbol(),
					   ev, NetEvProbe::POSEDGE, 1);
	    connect(po->pin(0), ex->pin(0));

	    des->add_node(po);

	      /* We want to wait only if the expression is something
		 other then 1 (0,x,z) . */
	    NetESignal*ce = new NetESignal(ex);
	    NetCondit*co = new NetCondit(ce, 0, we);

	    ev->set_line(*this);
	    we->set_line(*this);
	    co->set_line(*this);

	      /* If we don't have a sub-statement after all, then we
		 don't really need the block and we can save the
		 node. (i.e. wait (foo==1) ;) However, the common case
		 has a statement in the wait so we create a sequential
		 block to join the wait and the statement. */

	    if (enet) {
		  NetBlock*bl = new NetBlock(NetBlock::SEQU, 0);
		  bl->set_line(*this);
		  bl->append(co);
		  bl->append(enet);
		  return bl;
	    }

	    return co;
      }


	/* Handle the special case of an event name as an identifier
	   in an expression. Make a named event reference. */

      if (expr_.count() == 1) {
	    assert(expr_[0]->expr());
	    PEIdent*id = dynamic_cast<PEIdent*>(expr_[0]->expr());
	    NetEvent*ev;
	    if (id && (ev = scope->find_event(id->path()))) {
		  NetEvWait*pr = new NetEvWait(enet);
		  pr->add_event(ev);
		  pr->set_line(*this);
		  return pr;
	    }
      }

	/* Create A single NetEvent and NetEvWait. Then, create a
	   NetEvProbe for each conjunctive event in the event
	   list. The NetEvProbe object al refer back to the NetEvent
	   object. */

      NetEvent*ev = new NetEvent(scope->local_symbol());
      ev->set_line(*this);
      unsigned expr_count = 0;

      NetEvWait*wa = new NetEvWait(enet);
      wa->set_line(*this);

	/* If there are no expressions, this is a signal that it is an
	   @* statement. Generate an expression to use. */

      if (expr_.count() == 0) {
	    assert(enet);
	    NexusSet*nset = enet->nex_input();
	    if (nset == 0) {
		  cerr << get_line() << ": internal error: No NexusSet"
		       << " from statement." << endl;
		  enet->dump(cerr, 6);
		  des->errors += 1;
		  return enet;
	    }

	    if (nset->count() == 0) {
		  cerr << get_line() << ": warning: No inputs to statement."
		       << " Ignoring @*." << endl;
		  return enet;
	    }

	    NetEvProbe*pr = new NetEvProbe(scope, scope->local_hsymbol(),
					   ev, NetEvProbe::ANYEDGE,
					   nset->count());
	    for (unsigned idx = 0 ;  idx < nset->count() ;  idx += 1)
		  connect(nset[0][idx], pr->pin(idx));

	    delete nset;
	    des->add_node(pr);

	    expr_count = 1;

      } else for (unsigned idx = 0 ;  idx < expr_.count() ;  idx += 1) {

	    assert(expr_[idx]->expr());

	      /* If the expression is an identifier that matches a
		 named event, then handle this case all at once at
		 skip the rest of the expression handling. */

	    if (PEIdent*id = dynamic_cast<PEIdent*>(expr_[idx]->expr())) {
		  NetEvent*tmp = scope->find_event(id->path());
		  if (tmp) {
			wa->add_event(tmp);
			continue;
		  }
	    }

	      /* So now we have a normal event expression. Elaborate
		 the sub-expression as a net and decide how to handle
		 the edge. */

	    bool save_flag = error_implicit;
	    error_implicit = true;
	    NetNet*expr = expr_[idx]->expr()->elaborate_net(des, scope,
							    0, 0, 0, 0);
	    error_implicit = save_flag;
	    if (expr == 0) {
		  expr_[idx]->dump(cerr);
		  cerr << endl;
		  des->errors += 1;
		  continue;
	    }
	    assert(expr);

	    unsigned pins = (expr_[idx]->type() == PEEvent::ANYEDGE)
		  ? expr->pin_count() : 1;

	    NetEvProbe*pr;
	    switch (expr_[idx]->type()) {
		case PEEvent::POSEDGE:
		  pr = new NetEvProbe(scope, scope->local_hsymbol(), ev,
				      NetEvProbe::POSEDGE, pins);
		  break;

		case PEEvent::NEGEDGE:
		  pr = new NetEvProbe(scope, scope->local_hsymbol(), ev,
				      NetEvProbe::NEGEDGE, pins);
		  break;

		case PEEvent::ANYEDGE:
		  pr = new NetEvProbe(scope, scope->local_hsymbol(), ev,
				      NetEvProbe::ANYEDGE, pins);
		  break;

		default:
		  assert(0);
	    }

	    for (unsigned p = 0 ;  p < pr->pin_count() ; p += 1)
		  connect(pr->pin(p), expr->pin(p));

	    des->add_node(pr);
	    expr_count += 1;
      }

	/* If there was at least one conjunction that was an
	   expression (and not a named event) then add this
	   event. Otherwise, we didn't use it so delete it. */
      if (expr_count > 0) {
	    if (NetEvent*match = ev->find_similar_event()) {
		  delete ev;
		  wa->add_event(match);

	    } else {

		  scope->add_event(ev);
		  wa->add_event(ev);
	    }
      } else {
	    delete ev;
      }

      return wa;
}

NetProc* PEventStatement::elaborate(Design*des, NetScope*scope) const
{
      NetProc*enet = 0;
      if (statement_) {
	    enet = statement_->elaborate(des, scope);
	    if (enet == 0)
		  return 0;
      }

      return elaborate_st(des, scope, enet);
}

/*
 * Forever statements are represented directly in the netlist. It is
 * theoretically possible to use a while structure with a constant
 * expression to represent the loop, but why complicate the code
 * generators so?
 */
NetProc* PForever::elaborate(Design*des, NetScope*scope) const
{
      NetProc*stat = statement_->elaborate(des, scope);
      if (stat == 0) return 0;

      NetForever*proc = new NetForever(stat);
      return proc;
}

NetProc* PForce::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetNet*lval = lval_->elaborate_net(des, scope, 0, 0, 0, 0);
      if (lval == 0)
	    return 0;

      NetNet*rval = expr_->elaborate_net(des, scope, lval->pin_count(),
					 0, 0, 0);
      if (rval == 0)
	    return 0;

      if (rval->pin_count() < lval->pin_count())
	    rval = pad_to_width(des, rval, lval->pin_count());

      NetForce* dev = new NetForce(scope, scope->local_hsymbol(), lval);
      des->add_node(dev);

      for (unsigned idx = 0 ;  idx < dev->pin_count() ;  idx += 1)
	    connect(dev->pin(idx), rval->pin(idx));

      return dev;
}

/*
 * elaborate the for loop as the equivalent while loop. This eases the
 * task for the target code generator. The structure is:
 *
 *     begin : top
 *       name1_ = expr1_;
 *       while (cond_) begin : body
 *          statement_;
 *          name2_ = expr2_;
 *       end
 *     end
 */
NetProc* PForStatement::elaborate(Design*des, NetScope*scope) const
{
      NetExpr*etmp;
      assert(scope);

      const PEIdent*id1 = dynamic_cast<const PEIdent*>(name1_);
      assert(id1);
      const PEIdent*id2 = dynamic_cast<const PEIdent*>(name2_);
      assert(id2);

      NetBlock*top = new NetBlock(NetBlock::SEQU, 0);

	/* make the expression, and later the initial assignment to
	   the condition variable. The statement in the for loop is
	   very specifically an assignment. */
      NetNet*sig = des->find_signal(scope, id1->path());
      if (sig == 0) {
	    cerr << id1->get_line() << ": register ``" << id1->path()
		 << "'' unknown in this context." << endl;
	    des->errors += 1;
	    return 0;
      }
      assert(sig);
      NetAssign_*lv = new NetAssign_(sig);

	/* Make the r-value of the initial assignment, and size it
	   properly. Then use it to build the assignment statement. */
      etmp = expr1_->elaborate_expr(des, scope);
      etmp->set_width(lv->lwidth());

      NetAssign*init = new NetAssign(lv, etmp);

      top->append(init);

      NetBlock*body = new NetBlock(NetBlock::SEQU, 0);

	/* Elaborate the statement that is contained in the for
	   loop. If there is an error, this will return 0 and I should
	   skip the append. No need to worry, the error has been
	   reported so it's OK that the netlist is bogus. */
      NetProc*tmp = statement_->elaborate(des, scope);
      if (tmp)
	    body->append(tmp);


	/* Elaborate the increment assignment statement at the end of
	   the for loop. This is also a very specific assignment
	   statement. Put this into the "body" block. */
      sig = des->find_signal(scope, id2->path());
      assert(sig);
      lv = new NetAssign_(sig);

	/* Make the rvalue of the increment expression, and size it
	   for the lvalue. */
      etmp = expr2_->elaborate_expr(des, scope);
      etmp->set_width(lv->lwidth());
      NetAssign*step = new NetAssign(lv, etmp);

      body->append(step);


	/* Elaborate the condition expression. Try to evaluate it too,
	   in case it is a constant. This is an interesting case
	   worthy of a warning. */
      NetExpr*ce = cond_->elaborate_expr(des, scope);
      if (ce == 0) {
	    delete top;
	    return 0;
      }

      if (NetExpr*tmp = ce->eval_tree()) {
	    if (dynamic_cast<NetEConst*>(tmp)) {
		  cerr << get_line() << ": warning: condition expression "
			"of for-loop is constant." << endl;
	    }
	    ce = tmp;
      }


	/* All done, build up the loop. */

      NetWhile*loop = new NetWhile(ce, body);
      top->append(loop);
      return top;
}

/*
 * (See the PTask::elaborate methods for basic common stuff.)
 *
 * The return value of a function is represented as a reg variable
 * within the scope of the function that has the name of the
 * function. So for example with the function:
 *
 *    function [7:0] incr;
 *      input [7:0] in1;
 *      incr = in1 + 1;
 *    endfunction
 *
 * The scope of the function is <parent>.incr and there is a reg
 * variable <parent>.incr.incr. The elaborate_1 method is called with
 * the scope of the function, so the return reg is easily located.
 *
 * The function parameters are all inputs, except for the synthetic
 * output parameter that is the return value. The return value goes
 * into port 0, and the parameters are all the remaining ports.
 */

void PFunction::elaborate(Design*des, NetScope*scope) const
{
      NetFuncDef*def = scope->func_def();
      assert(def);

      NetProc*st = statement_->elaborate(des, scope);
      if (st == 0) {
	    cerr << statement_->get_line() << ": error: Unable to elaborate "
		  "statement in function " << def->name() << "." << endl;
	    des->errors += 1;
	    return;
      }

      def->set_proc(st);
}

NetProc* PRelease::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetNet*lval = lval_->elaborate_net(des, scope, 0, 0, 0, 0);
      if (lval == 0)
	    return 0;

      NetRelease*dev = new NetRelease(lval);
      dev->set_line( *this );
      return dev;
}

NetProc* PRepeat::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetExpr*expr = expr_->elaborate_expr(des, scope);
      if (expr == 0) {
	    cerr << get_line() << ": Unable to elaborate"
		  " repeat expression." << endl;
	    des->errors += 1;
	    return 0;
      }
      NetExpr*tmp = expr->eval_tree();
      if (tmp) {
	    delete expr;
	    expr = tmp;
      }

      NetProc*stat = statement_->elaborate(des, scope);
      if (stat == 0) return 0;

	// If the expression is a constant, handle certain special
	// iteration counts.
      if (NetEConst*ce = dynamic_cast<NetEConst*>(expr)) {
	    verinum val = ce->value();
	    switch (val.as_ulong()) {
		case 0:
		  delete expr;
		  delete stat;
		  return new NetBlock(NetBlock::SEQU, 0);
		case 1:
		  delete expr;
		  return stat;
		default:
		  break;
	    }
      }

      NetRepeat*proc = new NetRepeat(expr, stat);
      return proc;
}

/*
 * A task definition is elaborated by elaborating the statement that
 * it contains, and connecting its ports to NetNet objects. The
 * netlist doesn't really need the array of parameters once elaboration
 * is complete, but this is the best place to store them.
 *
 * The first elaboration pass finds the reg objects that match the
 * port names, and creates the NetTaskDef object. The port names are
 * in the form task.port.
 *
 *      task foo;
 *        output blah;
 *        begin <body> end
 *      endtask
 *
 * So in the foo example, the PWire objects that represent the ports
 * of the task will include a foo.blah for the blah port. This port is
 * bound to a NetNet object by looking up the name. All of this is
 * handled by the PTask::elaborate_sig method and the results stashed
 * in the created NetDaskDef attached to the scope.
 *
 * Elaboration pass 2 for the task definition causes the statement of
 * the task to be elaborated and attached to the NetTaskDef object
 * created in pass 1.
 *
 * NOTE: I am not sure why I bothered to prepend the task name to the
 * port name when making the port list. It is not really useful, but
 * that is what I did in pform_make_task_ports, so there it is.
 */

void PTask::elaborate(Design*des, NetScope*task) const
{
      NetTaskDef*def = task->task_def();
      assert(def);

      NetProc*st;
      if (statement_ == 0) {
	    cerr << get_line() << ": warning: task has no statement." << endl;
	    st = new NetBlock(NetBlock::SEQU, 0);

      } else {

	    st = statement_->elaborate(des, task);
	    if (st == 0) {
		  cerr << statement_->get_line() << ": Unable to elaborate "
			"statement in task " << task->name()
		       << " at " << get_line() << "." << endl;
		  return;
	    }
      }

      def->set_proc(st);
}

NetProc* PTrigger::elaborate(Design*des, NetScope*scope) const
{
      assert(scope);

      NetEvent*ev = scope->find_event(event_);
      if (ev == 0) {
	    cerr << get_line() << ": error: event <" << event_ << ">"
		 << " not found." << endl;
	    des->errors += 1;
	    return 0;
      }

      NetEvTrig*trig = new NetEvTrig(ev);
      trig->set_line(*this);
      return trig;
}

/*
 * The while loop is fairly directly represented in the netlist.
 */
NetProc* PWhile::elaborate(Design*des, NetScope*scope) const
{
      NetWhile*loop = new NetWhile(cond_->elaborate_expr(des, scope),
				   statement_->elaborate(des, scope));
      return loop;
}

/*
 * When a module is instantiated, it creates the scope then uses this
 * method to elaborate the contents of the module.
 */
bool Module::elaborate(Design*des, NetScope*scope) const
{
      bool result_flag = true;


	// Elaborate functions.
      typedef map<string,PFunction*>::const_iterator mfunc_it_t;
      for (mfunc_it_t cur = funcs_.begin()
		 ; cur != funcs_.end() ;  cur ++) {

	    NetScope*fscope = scope->child((*cur).first);
	    assert(fscope);
	    (*cur).second->elaborate(des, fscope);
      }

	// Elaborate the task definitions. This is done before the
	// behaviors so that task calls may reference these, and after
	// the signals so that the tasks can reference them.
      typedef map<string,PTask*>::const_iterator mtask_it_t;
      for (mtask_it_t cur = tasks_.begin()
		 ; cur != tasks_.end() ;  cur ++) {

	    NetScope*tscope = scope->child((*cur).first);
	    assert(tscope);
	    (*cur).second->elaborate(des, tscope);
      }

	// Get all the gates of the module and elaborate them by
	// connecting them to the signals. The gate may be simple or
	// complex.
      const list<PGate*>&gl = get_gates();

      for (list<PGate*>::const_iterator gt = gl.begin()
		 ; gt != gl.end()
		 ; gt ++ ) {

	    (*gt)->elaborate(des, scope);
      }

	// Elaborate the behaviors, making processes out of them. This
	// involves scanning the PProcess* list, creating a NetProcTop
	// for each process.
      const list<PProcess*>&sl = get_behaviors();

      for (list<PProcess*>::const_iterator st = sl.begin()
		 ; st != sl.end()
		 ; st ++ ) {

	    NetProc*cur = (*st)->statement()->elaborate(des, scope);
	    if (cur == 0) {
		  result_flag = false;
		  continue;
	    }

	    NetProcTop*top;
	    switch ((*st)->type()) {
		case PProcess::PR_INITIAL:
		  top = new NetProcTop(scope, NetProcTop::KINITIAL, cur);
		  break;
		case PProcess::PR_ALWAYS:
		  top = new NetProcTop(scope, NetProcTop::KALWAYS, cur);
		  break;
	    }

	      // Evaluate the attributes for this process, if there
	      // are any. These attributes are to be attached to the
	      // NetProcTop object.
	    struct attrib_list_t*attrib_list = 0;
	    unsigned attrib_list_n = 0;
	    attrib_list = evaluate_attributes((*st)->attributes,
					      attrib_list_n,
					      des, scope);

	    for (unsigned adx = 0 ;  adx < attrib_list_n ;  adx += 1)
		  top->attribute(attrib_list[adx].key,
				 attrib_list[adx].val);

	    delete[]attrib_list;

	    top->set_line(*(*st));
	    des->add_process(top);
      }

      return result_flag;
}

struct root_elem {
      Module *mod;
      NetScope *scope;
};

Design* elaborate(list<const char*>roots)
{
      svector<root_elem*> root_elems(roots.size());
      bool rc = true;
      unsigned i = 0;

	// This is the output design. I fill it in as I scan the root
	// module and elaborate what I find.
      Design*des = new Design;

      for (list<const char*>::const_iterator root = roots.begin()
		 ; root != roots.end()
		 ; root++) {

	      // Look for the root module in the list.
	    map<string,Module*>::const_iterator mod = pform_modules.find(*root);
	    if (mod == pform_modules.end()) {
		  cerr << "error: Unable to find the root module \""
		       << (*root) << "\" in the Verilog source." << endl; 
		  cerr << "     : Perhaps ``-s " << (*root)
		       << "'' is incorrect?" << endl;
		  des->errors++;
		  continue;
	    }

	    Module *rmod = (*mod).second;
	    
	    // Make the root scope, then scan the pform looking for scopes
	    // and parameters. 
	    NetScope*scope = des->make_root_scope(*root);
	    scope->time_unit(rmod->time_unit);
	    scope->time_precision(rmod->time_precision);
	    des->set_precision(rmod->time_precision);
	    if (! rmod->elaborate_scope(des, scope)) {
		  delete des;
		  return 0;
	    }

	    struct root_elem *r = new struct root_elem;
	    r->mod = rmod;
	    r->scope = scope;
	    root_elems[i++] = r;
      }

	// Errors already? Probably missing root modules. Just give up
	// now and return nothing.
      if (des->errors > 0) {
	    delete des;
	    return 0;
      }

	// This method recurses through the scopes, looking for
	// defparam assignments to apply to the parameters in the
	// various scopes. This needs to be done after all the scopes
	// and basic parameters are taken care of because the defparam
	// can assign to a paramter declared *after* it.
      des->run_defparams();


	// At this point, all parameter overrides are done. Scane the
	// scopes and evaluate the parameters all the way down to
	// constants.
      des->evaluate_parameters();

	// With the parameters evaluated down to constants, we have
	// what we need to elaborate signals and memories. This pass
	// creates all the NetNet and NetMemory objects for declared
	// objects.
      for (i = 0; i < root_elems.count(); i++) {
	    Module *rmod = root_elems[i]->mod;
	    NetScope *scope = root_elems[i]->scope;

	    if (! rmod->elaborate_sig(des, scope)) {
		  delete des;
		  return 0;
	    }
      }

	// Now that the structure and parameters are taken care of,
	// run through the pform again and generate the full netlist.
      for (i = 0; i < root_elems.count(); i++) {
	    Module *rmod = root_elems[i]->mod;
	    NetScope *scope = root_elems[i]->scope;

	    rc &= rmod->elaborate(des, scope);
      }


      if (rc == false) {
	    delete des;
	    des = 0;
      }

      return des;
}


/*
 * $Log: elaborate.cc,v $
 * Revision 1.254  2002/06/19 04:20:03  steve
 *  Remove NetTmp and add NetSubnet class.
 *
 * Revision 1.253  2002/06/05 03:44:25  steve
 *  Add support for memory words in l-value of
 *  non-blocking assignments, and remove the special
 *  NetAssignMem_ and NetAssignMemNB classes.
 *
 * Revision 1.252  2002/06/04 05:38:44  steve
 *  Add support for memory words in l-value of
 *  blocking assignments, and remove the special
 *  NetAssignMem class.
 *
 * Revision 1.251  2002/05/27 00:08:45  steve
 *  Support carrying the scope of named begin-end
 *  blocks down to the code generator, and have
 *  the vvp code generator use that to support disable.
 *
 * Revision 1.250  2002/05/26 01:39:02  steve
 *  Carry Verilog 2001 attributes with processes,
 *  all the way through to the ivl_target API.
 *
 *  Divide signal reference counts between rval
 *  and lval references.
 *
 * Revision 1.249  2002/05/23 03:08:51  steve
 *  Add language support for Verilog-2001 attribute
 *  syntax. Hook this support into existing $attribute
 *  handling, and add number and void value types.
 *
 *  Add to the ivl_target API new functions for access
 *  of complex attributes attached to gates.
 *
 * Revision 1.248  2002/05/12 19:16:58  steve
 *  Accept errors in memory index expression.
 *
 * Revision 1.247  2002/05/07 05:06:07  steve
 *  Use else clause instead of ! to preface wait events.
 *
 * Revision 1.246  2002/04/24 17:40:48  steve
 *  Agressively evalutate case expressions.
 *
 * Revision 1.245  2002/04/22 00:53:39  steve
 *  Do not allow implicit wires in sensitivity lists.
 *
 * Revision 1.244  2002/04/21 22:31:02  steve
 *  Redo handling of assignment internal delays.
 *  Leave it possible for them to be calculated
 *  at run time.
 *
 * Revision 1.243  2002/04/21 04:59:07  steve
 *  Add support for conbinational events by finding
 *  the inputs to expressions and some statements.
 *  Get case and assignment statements working.
 *
 * Revision 1.242  2002/04/13 02:33:17  steve
 *  Detect missing indices to memories (PR#421)
 *
 * Revision 1.241  2002/03/09 04:02:26  steve
 *  Constant expressions are not l-values for task ports.
 *
 * Revision 1.240  2002/01/23 05:56:22  steve
 *  elaborate deassign lval as done for assign.
 *
 * Revision 1.239  2002/01/19 20:09:56  steve
 *  Evaluate case guards, if possible.
 *
 * Revision 1.238  2001/12/31 00:39:20  steve
 *  Remove test print
 *
 * Revision 1.237  2001/12/29 20:19:31  steve
 *  Do not delete delay expressions of UDP instances.
 *
 * Revision 1.236  2001/12/06 05:04:49  steve
 *  Forgot to evaluate UDP delays.
 *
 * Revision 1.235  2001/12/06 04:44:11  steve
 *  Support delays on UDP instances.
 *
 * Revision 1.234  2001/12/03 04:47:14  steve
 *  Parser and pform use hierarchical names as hname_t
 *  objects instead of encoded strings.
 *
 * Revision 1.233  2001/11/22 06:20:59  steve
 *  Use NetScope instead of string for scope path.
 *
 * Revision 1.232  2001/11/08 05:15:50  steve
 *  Remove string paths from PExpr elaboration.
 *
 * Revision 1.231  2001/11/07 04:26:46  steve
 *  elaborate_lnet uses scope instead of string path.
 *
 * Revision 1.230  2001/11/07 04:01:59  steve
 *  eval_const uses scope instead of a string path.
 *
 * Revision 1.229  2001/11/04 23:12:29  steve
 *  Pad limited r-values in continuous assignments.
 *
 * Revision 1.228  2001/10/31 03:22:31  steve
 *  Give up if roots are missing.
 *
 * Revision 1.227  2001/10/28 01:14:53  steve
 *  NetObj constructor finally requires a scope.
 *
 * Revision 1.226  2001/10/22 23:26:37  steve
 *  Better error message for mising root module.
 *
 * Revision 1.225  2001/10/22 02:05:20  steve
 *  Handle activating tasks in another root.
 *
 * Revision 1.224  2001/10/21 00:42:47  steve
 *  Module types in pform are char* instead of string.
 *
 * Revision 1.223  2001/10/20 23:02:40  steve
 *  Add automatic module libraries.
 *
 * Revision 1.222  2001/10/20 05:21:51  steve
 *  Scope/module names are char* instead of string.
 *
 * Revision 1.221  2001/10/19 21:53:24  steve
 *  Support multiple root modules (Philip Blundell)
 */