Fix for assertion error when expanding macro.

[iverilog.git] / synth2.cc

/*
 * Copyright (c) 2002-2005 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: synth2.cc,v 1.46 2007/03/22 16:08:17 steve Exp $"
#endif

# include "config.h"

# include  "functor.h"
# include  "netlist.h"
# include  "netmisc.h"
# include  "compiler.h"
# include  <assert.h>


bool NetProc::synth_async(Design*des, NetScope*scope,
                          const NetBus&nex_map, NetBus&nex_out)
{
      return false;
}

bool NetProc::synth_sync(Design*des, NetScope*scope, NetFF*ff,
                         const NetBus&nex_map, NetBus&nex_out,
                         const svector<NetEvProbe*>&events)
{
      if (events.count() > 0) {
            cerr << get_line() << ": error: Events are unaccounted"
                 << " for in process synthesis." << endl;
            des->errors += 1;
      }

        /* Synthesize the input to the DFF. */
      return synth_async(des, scope, nex_map, nex_out);
}

#if 0
static unsigned find_nexus_in_set(const NetBus&nset, const Nexus*nex)
{
      unsigned idx = 0;
      for (idx = 0 ;  idx < nset.pin_count() ;  idx += 1)
            if (nset.pin(idx).nexus() == nex)
                  return idx;

      return idx;
}
#endif

/*
 * Async synthesis of assignments is done by synthesizing the rvalue
 * expression, then connecting the l-value directly to the output of
 * the r-value.
 *
 * The nex_map is the O-set for the statement, and lists the positions
 * of the outputs as the caller wants results linked up. The nex_out,
 * however, is the set of nexa that are to actually get linked to the
 * r-value.
 */
bool NetAssignBase::synth_async(Design*des, NetScope*scope,
                                const NetBus&nex_map, NetBus&nex_out)
{
      NetNet*rsig = rval_->synthesize(des);
      assert(rsig);

      NetNet*lsig = lval_->sig();
      if (!lsig) {
            cerr << get_line() << ": error: "
                 << "NetAssignBase::synth_async on unsupported lval ";
            dump_lval(cerr);
            cerr << endl;
            des->errors += 1;
            return false;
      }
      assert(lval_->more == 0);

      if (debug_synth2) {
            cerr << get_line() << ": debug: l-value signal is "
                 << lsig->vector_width() << " bits, r-value signal is "
                 << rsig->vector_width() << " bits." << endl;
      }

#if 0
        /* The l-value and r-value map must have the same width. */
      if (lval_->lwidth() != nex_map->vector_width()) {
            cerr << get_line() << ": error: Assignment synthesis: "
                 << "vector width mismatch, "
                 << lval_->lwidth() << " bits != "
                 << nex_map->vector_width() << " bits." << endl;
            return false;
      }
#else
        /* For now, assume there is exactly one output. */
      assert(nex_out.pin_count() == 1);
#endif

      connect(nex_out.pin(0), rsig->pin(0));

        /* This lval_ represents a reg that is a WIRE in the
           synthesized results. This function signals the destructor
           to change the REG that this l-value refers to into a
           WIRE. It is done then, at the last minute, so that pending
           synthesis can continue to work with it as a WIRE. */
      lval_->turn_sig_to_wire_on_release();

      return true;
}

/*
 * Sequential blocks are translated to asynchronous logic by
 * translating each statement of the block, in order, into gates. The
 * nex_out for the block is the union of the nex_out for all the
 * substatements.
 */
bool NetBlock::synth_async(Design*des, NetScope*scope,
                           const NetBus&nex_map, NetBus&nex_out)
{
      if (last_ == 0) {
            return true;
      }

      bool flag = true;
      NetProc*cur = last_;
      do {
            cur = cur->next_;

              /* Create a temporary map of the output only from this
                 statement. */
            NexusSet tmp_set;
            cur->nex_output(tmp_set);
            NetBus tmp_map (scope, tmp_set.count());
            for (unsigned idx = 0 ;  idx < tmp_set.count() ;  idx += 1)
                  connect(tmp_set[idx], tmp_map.pin(idx));

              /* Create also a temporary NetBus to collect the
                 output from the synthesis. */
            NetBus tmp_out (scope, tmp_set.count());

            bool ok_flag = cur->synth_async(des, scope, tmp_map, tmp_out);

            flag = flag && ok_flag;
            if (ok_flag == false)
                  continue;

              /* Now find the tmp_map pins in the nex_map global map,
                 and use that to direct the connection to the nex_out
                 output bus. Look for the nex_map pin that is linked
                 to the tmp_map.pin(idx) pin, and link that to the
                 tmp_out.pin(idx) output link. */
            for (unsigned idx = 0 ;  idx < tmp_out.pin_count() ;  idx += 1) {
                  unsigned ptr = 0;
                  while (ptr < nex_map.pin_count()
                         && ! nex_map.pin(ptr).is_linked(tmp_map.pin(idx)))
                        ptr += 1;

                  assert(ptr < nex_out.pin_count());
                  connect(nex_out.pin(ptr), tmp_out.pin(idx));
            }

      } while (cur != last_);

      return flag;
}

bool NetCase::synth_async(Design*des, NetScope*scope,
                          const NetBus&nex_map, NetBus&nex_out)
{
        /* Synthesize the select expression. */
      NetNet*esig = expr_->synthesize(des);

      unsigned sel_width = esig->vector_width();
      assert(sel_width > 0);

      unsigned mux_width = 0;
      for (unsigned idx = 0 ;  idx < nex_out.pin_count() ;  idx += 1)
            mux_width += nex_out.pin(idx).nexus()->vector_width();

        /* Collect all the statements into a map of index to
           statement. The guard expression it evaluated to be the
           index of the mux value, and the statement is bound to that
           index. */

      unsigned long max_guard_value = 0;
      map<unsigned long,NetProc*>statement_map;
      NetProc*statement_default = 0;

      for (unsigned item = 0 ;  item < nitems_ ;  item += 1) {
            if (items_[item].guard == 0) {
                  statement_default = items_[item].statement;
                  continue;
            }

            NetEConst*ge = dynamic_cast<NetEConst*>(items_[item].guard);
            assert(ge);
            verinum gval = ge->value();

            unsigned sel_idx = gval.as_ulong();

            assert(items_[item].statement);
            statement_map[sel_idx] = items_[item].statement;

            if (sel_idx > max_guard_value)
                  max_guard_value = sel_idx;
      }

      unsigned mux_size = max_guard_value + 1;

      NetMux*mux = new NetMux(scope, scope->local_symbol(),
                              mux_width, mux_size, sel_width);
      des->add_node(mux);

        /* The select signal is already synthesized. Simply hook it up. */
      connect(mux->pin_Sel(), esig->pin(0));

        /* For now, assume that the output is only 1 signal. */
      assert(nex_out.pin_count() == 1);
      connect(mux->pin_Result(), nex_out.pin(0));

        /* For now, only support logic types. */
      ivl_variable_type_t mux_data_type = IVL_VT_LOGIC;

        /* Forgot to support default statements? */
      assert(statement_default == 0);

      NetNet*isig;
      for (unsigned idx = 0 ;  idx < mux_size ;  idx += 1) {

            NetProc*stmt = statement_map[idx];
            if (stmt == 0) {
                  cerr << get_line() << ": error: case " << idx
                       << " is not accounted for in asynchronous mux." << endl;
                  des->errors += 1;
                  continue;
            }

            isig = new NetNet(scope, scope->local_symbol(),
                              NetNet::TRI, mux_width);
            isig->local_flag(true);
            isig->data_type(mux_data_type);

            connect(mux->pin_Data(idx), isig->pin(0));

            NetBus tmp (scope, 1);
            connect(tmp.pin(0), isig->pin(0));
            stmt->synth_async(des, scope, tmp, tmp);
      }

      return true;
}

bool NetCondit::synth_async(Design*des, NetScope*scope,
                            const NetBus&nex_map, NetBus&nex_out)
{
#if 0
      NetNet*ssig = expr_->synthesize(des);
      assert(ssig);

      if (if_ == 0) {
            DEBUG_SYNTH2_EXIT("NetCondit",false)
            return false;
      }
      if (else_ == 0) {
            cerr << get_line() << ": error: Asynchronous if statement"
                 << " is missing the else clause." << endl;
            DEBUG_SYNTH2_EXIT("NetCondit",false)
            return false;
      }

      assert(if_ != 0);
      assert(else_ != 0);

      NetNet*asig = new NetNet(scope, scope->local_symbol(),
                               NetNet::WIRE, nex_map->pin_count());
      asig->local_flag(true);

      bool flag;
      flag = if_->synth_async(des, scope, nex_map, asig);
      if (!flag) {
            delete asig;
            DEBUG_SYNTH2_EXIT("NetCondit",false)
            return false;
      }

      NetNet*bsig = new NetNet(scope, scope->local_symbol(),
                               NetNet::WIRE, nex_map->pin_count());
      bsig->local_flag(true);

      flag = else_->synth_async(des, scope, nex_map, bsig);
      if (!flag) {
            delete asig;
            delete bsig;
            DEBUG_SYNTH2_EXIT("NetCondit",false)
            return false;
      }

      NetMux*mux = new NetMux(scope, scope->local_symbol(),
                              nex_out->vector_width(), 2, 1);

      connect(mux->pin_Sel(),   ssig->pin(0));
      connect(mux->pin_Data(1), asig->pin(0));
      connect(mux->pin_Data(0), bsig->pin(0));
      connect(nex_out->pin(0), mux->pin_Result());

      des->add_node(mux);

      DEBUG_SYNTH2_EXIT("NetCondit",true)
      return true;

#else
      cerr << get_line() << ": sorry: "
           << "Forgot to implement NetCondit::synth_async" << endl;
      des->errors += 1;
      return false;
#endif
}

bool NetEvWait::synth_async(Design*des, NetScope*scope,
                            const NetBus&nex_map, NetBus&nex_out)
{
      bool flag = statement_->synth_async(des, scope, nex_map, nex_out);
      return flag;
}

/*
 * This method is called when the process is shown to be
 * asynchronous. Figure out the nexus set of outputs from this
 * process, and pass that to the synth_async method for the statement
 * of the process. The statement will connect its output to the
 * nex_out set, using the nex_map as a guide. Starting from the top,
 * the nex_map is the same as the nex_map.
 */
bool NetProcTop::synth_async(Design*des)
{
      NexusSet nex_set;
      statement_->nex_output(nex_set);

      if (debug_synth2) {
            cerr << get_line() << ": debug: Process has "
                 << nex_set.count() << " outputs." << endl;
      }

      NetBus nex_q (scope(), nex_set.count());
      for (unsigned idx = 0 ;  idx < nex_set.count() ;  idx += 1) {
            connect(nex_set[idx], nex_q.pin(idx));
      }

      bool flag = statement_->synth_async(des, scope(), nex_q, nex_q);
      return flag;
}

/*
 * This method is called when a block is encountered near the surface
 * of a synchronous always statement. For example, this code will be
 * invoked for input like this:
 *
 *     always @(posedge clk...) begin
 *           <statement1>
 *           <statement2>
 *           ...
 *     end
 *
 * This needs to be split into a DFF bank for each statement, because
 * the statements may each infer different reset and enable signals.
 */
bool NetBlock::synth_sync(Design*des, NetScope*scope, NetFF*ff,
                           const NetBus&nex_map, NetBus&nex_out,
                           const svector<NetEvProbe*>&events_in)
{
      if (last_ == 0) {
            return true;
      }

#if 0
      bool flag = true;

      const perm_string tmp1 = perm_string::literal("tmp1");
      const perm_string tmp2 = perm_string::literal("tmp2");

        /* Keep an accounting of which statement accounts for which
           bit slice of the FF bank. This is used for error checking. */
      NetProc**pin_accounting = new NetProc* [ff->pin_count()];
      for (unsigned idx = 0 ;  idx < ff->pin_count() ;  idx += 1)
            pin_accounting[idx] = 0;

      NetProc*cur = last_;
      do {
            cur = cur->next_;

              /* Create a temporary nex_map for the substatement. */
            NexusSet tmp_set;
            cur->nex_output(tmp_set);
            NetNet*tmp_map = new NetNet(scope, tmp1, NetNet::WIRE,
                                        tmp_set.count());
            for (unsigned idx = 0 ;  idx < tmp_map->pin_count() ;  idx += 1)
                  connect(tmp_set[idx], tmp_map->pin(idx));

              /* NOTE: After this point, tmp_set should not be used as
                 the various functions I call do a lot of connecting,
                 and the nexa in the tmp_set may get realloced. Use
                 the tmp_map instead. */

              /* Create also a temporary net_out to collect the
                 output. The tmp1 and tmp2 map and out sets together
                 are used to collect the outputs from the substatement
                 for the inputs of the FF bank. */
            NetNet*tmp_out = new NetNet(scope, tmp2, NetNet::WIRE,
                                        tmp_map->pin_count());

            verinum tmp_aset = ff->aset_value();
            verinum tmp_sset = ff->sset_value();

              /* Create a new DFF to handle this part of the begin-end
                 block. Connect this NetFF to the associated pins of
                 the existing wide NetFF device. While I'm at it, also
                 copy the aset_value bits for the new ff device. */
            NetFF*ff2 = new NetFF(scope, scope->local_symbol(),
                                  tmp_out->pin_count());
            des->add_node(ff2);

            verinum aset_value2 (verinum::V1, ff2->width());
            verinum sset_value2 (verinum::V1, ff2->width());
            for (unsigned idx = 0 ;  idx < ff2->width() ;  idx += 1) {
                  unsigned ptr = find_nexus_in_set(nex_map,
                                                   tmp_map->pin(idx).nexus());

                    /* Connect Data and Q bits to the new FF. */
                  connect(ff->pin_Data(ptr), ff2->pin_Data(idx));
                  connect(ff->pin_Q(ptr), ff2->pin_Q(idx));

                    /* Copy the asynch set bit to the new device. */
                  if (ptr < tmp_aset.len())
                        aset_value2.set(idx, tmp_aset[ptr]);

                    /* Copy the synch set bit to the new device. */
                  if (ptr < tmp_sset.len())
                        sset_value2.set(idx, tmp_sset[ptr]);

                  if (pin_accounting[ptr] != 0) {
                        cerr << cur->get_line() << ": error: "
                             << "Synchronous output conflicts with "
                             << pin_accounting[ptr]->get_line()
                             << "." << endl;
                        flag = false;

                  } else {
                        pin_accounting[ptr] = cur;
                  }
            }

            if (ff->pin_Aclr().is_linked())
                  connect(ff->pin_Aclr(),  ff2->pin_Aclr());
            if (ff->pin_Aset().is_linked())
                  connect(ff->pin_Aset(),  ff2->pin_Aset());
            if (ff->pin_Sclr().is_linked())
                  connect(ff->pin_Sclr(),  ff2->pin_Sclr());
            if (ff->pin_Sset().is_linked())
                  connect(ff->pin_Sset(),  ff2->pin_Sset());
            if (ff->pin_Clock().is_linked())
                  connect(ff->pin_Clock(), ff2->pin_Clock());
            if (ff->pin_Enable().is_linked())
                  connect(ff->pin_Enable(),ff2->pin_Enable());

              /* Remember to store the aset value into the new FF. If
                 this leads to an Aset value of 0 (and Aclr is not
                 otherwise used) then move the Aset input to Aclr. */
            if (tmp_aset.len() == ff->width()) {

                  if (aset_value2.is_zero()
                      && ff2->pin_Aset().is_linked()
                      && !ff2->pin_Aclr().is_linked()) {

                        connect(ff2->pin_Aclr(), ff2->pin_Aset());
                        ff2->pin_Aset().unlink();

                  } else {
                        ff2->aset_value(aset_value2);
                  }
            }

              /* Now go on with the synchronous synthesis for this
                 subset of the statement. The tmp_map is the output
                 nexa that we expect, and the tmp_out is where we want
                 those outputs connected. */
            bool ok_flag = cur->synth_sync(des, scope, ff2, tmp_map,
                                           tmp_out, events_in);
            flag = flag && ok_flag;

            if (ok_flag == false)
                  continue;

              /* Use the nex_map to link up the output from the
                 substatement to the output of the block as a
                 whole. It is occasionally possible to have outputs
                 beyond the input set, for example when the l-value of
                 an assignment is smaller then the r-value. */
            for (unsigned idx = 0 ;  idx < tmp_out->pin_count() ; idx += 1) {
                  unsigned ptr = find_nexus_in_set(nex_map,
                                                   tmp_map->pin(idx).nexus());

                  if (ptr < nex_out->pin_count())
                        connect(nex_out->pin(ptr), tmp_out->pin(idx));
            }

            delete tmp_map;
            delete tmp_out;

      } while (cur != last_);

      delete[]pin_accounting;

        /* Done. The large NetFF is no longer needed, as it has been
           taken up by the smaller NetFF devices. */
      delete ff;

      return flag;

#else
      cerr << get_line() << ": sorry: "
           << "Forgot to implement NetBlock::synth_sync"
           << endl;
      des->errors += 1;
      return false;
#endif
}

/*
 * This method handles the case where I find a conditional near the
 * surface of a synchronous thread. This conditional can be a CE or an
 * asynchronous set/reset, depending on whether the pin of the
 * expression is connected to an event, or not.
 */
bool NetCondit::synth_sync(Design*des, NetScope*scope, NetFF*ff,
                           const NetBus&nex_map, NetBus&nex_out,
                           const svector<NetEvProbe*>&events_in)
{
#if 0
        /* First try to turn the condition expression into an
           asynchronous set/reset. If the condition expression has
           inputs that are included in the sensitivity list, then it
           is likely intended as an asynchronous input. */

      NexusSet*expr_input = expr_->nex_input();
      assert(expr_input);
      for (unsigned idx = 0 ;  idx < events_in.count() ;  idx += 1) {

            NetEvProbe*ev = events_in[idx];
            NexusSet pin_set;
            pin_set.add(ev->pin(0).nexus());

            if (! expr_input->contains(pin_set))
                  continue;

              /* Ah, this edge is in the sensitivity list for the
                 expression, so we have an asynchronous
                 input. Synthesize the set/reset input expression. */

            NetNet*rst = expr_->synthesize(des);
            assert(rst->pin_count() == 1);

              /* XXXX I really should find a way to check that the
                 edge used on the reset input is correct. This would
                 involve interpreting the exression that is fed by the
                 reset expression. */
              //assert(ev->edge() == NetEvProbe::POSEDGE);

              /* Synthesize the true clause to figure out what
                 kind of set/reset we have. */
            NetNet*asig = new NetNet(scope, scope->local_symbol(),
                                     NetNet::WIRE, nex_map->pin_count());
            asig->local_flag(true);

            assert(if_ != 0);
            bool flag = if_->synth_async(des, scope, nex_map, asig);

            assert(asig->pin_count() == ff->width());

              /* Collect the set/reset value into a verinum. If
                 this turns out to be entirely 0 values, then
                 use the Aclr input. Otherwise, use the Aset
                 input and save the set value. */
            verinum tmp (verinum::V0, ff->width());
            for (unsigned bit = 0 ;  bit < ff->width() ;  bit += 1) {

                  assert(asig->pin(bit).nexus()->drivers_constant());
                  tmp.set(bit, asig->pin(bit).nexus()->driven_value());
            }

            assert(tmp.is_defined());
            if (tmp.is_zero()) {
                  connect(ff->pin_Aclr(), rst->pin(0));

            } else {
                  connect(ff->pin_Aset(), rst->pin(0));
                  ff->aset_value(tmp);
            }

            delete asig;
            delete expr_input;

            assert(events_in.count() == 1);
            assert(else_ != 0);
            flag = else_->synth_sync(des, scope, ff, nex_map,
                                     nex_out, svector<NetEvProbe*>(0))
                  && flag;
            DEBUG_SYNTH2_EXIT("NetCondit",flag)
            return flag;
      }

      delete expr_input;

        /* Detect the case that this is a *synchronous* set/reset. It
           is not asyncronous because we know the condition is not
           included in the sensitivity list, but if the if_ case is
           constant (has no inputs) then we can model this as a
           synchronous set/reset.

           This is only synchronous set/reset if there is a true and a
           false clause, and no inputs. The "no inputs" requirement is
           met if the assignments are of all constant values. */
      assert(if_ != 0);
      NexusSet*a_set = if_->nex_input();

      if ((a_set->count() == 0) && if_ && else_) {

            NetNet*rst = expr_->synthesize(des);
            assert(rst->pin_count() == 1);

              /* Synthesize the true clause to figure out what
                 kind of set/reset we have. */
            NetNet*asig = new NetNet(scope, scope->local_symbol(),
                                     NetNet::WIRE, nex_map->pin_count());
            asig->local_flag(true);
            bool flag = if_->synth_async(des, scope, nex_map, asig);

            if (!flag) {
                  /* This path leads nowhere */
                  delete asig;
            } else {
                  assert(asig->pin_count() == ff->width());

                    /* Collect the set/reset value into a verinum. If
                       this turns out to be entirely 0 values, then
                       use the Sclr input. Otherwise, use the Aset
                       input and save the set value. */
                  verinum tmp (verinum::V0, ff->width());
                  for (unsigned bit = 0 ;  bit < ff->width() ;  bit += 1) {

                        assert(asig->pin(bit).nexus()->drivers_constant());
                        tmp.set(bit, asig->pin(bit).nexus()->driven_value());
                  }

                  assert(tmp.is_defined());
                  if (tmp.is_zero()) {
                        connect(ff->pin_Sclr(), rst->pin(0));

                  } else {
                        connect(ff->pin_Sset(), rst->pin(0));
                        ff->sset_value(tmp);
                  }

                  delete a_set;

                  assert(else_ != 0);
                  flag = else_->synth_sync(des, scope, ff, nex_map,
                                           nex_out, svector<NetEvProbe*>(0))
                        && flag;
                  DEBUG_SYNTH2_EXIT("NetCondit",flag)
                  return flag;
            }
      }

      delete a_set;

        /* Failed to find an asynchronous set/reset, so any events
           input are probably in error. */
      if (events_in.count() > 0) {
            cerr << get_line() << ": error: Events are unaccounted"
                 << " for in process synthesis." << endl;
            des->errors += 1;
      }


        /* If this is an if/then/else, then it is likely a
           combinational if, and I should synthesize it that way. */
      if (if_ && else_) {
            bool flag = synth_async(des, scope, nex_map, nex_out);
            DEBUG_SYNTH2_EXIT("NetCondit",flag)
            return flag;
      }

      assert(if_);
      assert(!else_);

        /* Synthesize the enable expression. */
      NetNet*ce = expr_->synthesize(des);
      assert(ce->pin_count() == 1);

        /* What's left, is a synchronous CE statement like this:

             if (expr_) <true statement>;

           The expr_ expression has already been synthesized to the ce
           net, so we connect it here to the FF. What's left is to
           synthesize the substatement as a combinational
           statement.

           Watch out for the special case that there is already a CE
           connected to this FF. This can be caused by code like this:

             if (a) if (b) <statement>;

           In this case, we are working on the inner IF, so we AND the
           a and b expressions to make a new CE. */

      if (ff->pin_Enable().is_linked()) {
            NetLogic*ce_and = new NetLogic(scope,
                                           scope->local_symbol(), 3,
                                           NetLogic::AND, 1);
            des->add_node(ce_and);
            connect(ff->pin_Enable(), ce_and->pin(1));
            connect(ce->pin(0), ce_and->pin(2));

            ff->pin_Enable().unlink();
            connect(ff->pin_Enable(), ce_and->pin(0));

            NetNet*tmp = new NetNet(scope, scope->local_symbol(),
                                    NetNet::IMPLICIT, 1);
            tmp->local_flag(true);
            connect(ff->pin_Enable(), tmp->pin(0));

      } else {

            connect(ff->pin_Enable(), ce->pin(0));
      }

      bool flag = if_->synth_sync(des, scope, ff, nex_map, nex_out, events_in);

      return flag;

#else
      cerr << get_line() << ": sorry: "
           << "Forgot to implement NetCondit::synth_sync" << endl;
      des->errors += 1;
      return false;
#endif
}

bool NetEvWait::synth_sync(Design*des, NetScope*scope, NetFF*ff,
                           const NetBus&nex_map, NetBus&nex_out,
                           const svector<NetEvProbe*>&events_in)
{
      if (events_in.count() > 0) {
            cerr << get_line() << ": error: Events are unaccounted"
                 << " for in process synthesis." << endl;
            des->errors += 1;
      }

      assert(events_in.count() == 0);

        /* This can't be other than one unless there are named events,
           which I cannot synthesize. */
      assert(nevents_ == 1);
      NetEvent*ev = events_[0];

      assert(ev->nprobe() >= 1);
      svector<NetEvProbe*>events (ev->nprobe() - 1);

        /* Get the input set from the substatement. This will be used
           to figure out which of the probes is the clock. */
      NexusSet*statement_input = statement_ -> nex_input();

        /* Search for a clock input. The clock input is the edge event
           that is not also an input to the substatement. */
      NetEvProbe*pclk = 0;
      unsigned event_idx = 0;
      for (unsigned idx = 0 ;  idx < ev->nprobe() ;  idx += 1) {
            NetEvProbe*tmp = ev->probe(idx);
            assert(tmp->pin_count() == 1);

            NexusSet tmp_nex;
            tmp_nex .add( tmp->pin(0).nexus() );

            if (! statement_input ->contains(tmp_nex)) {
                  if (pclk != 0) {
                        cerr << get_line() << ": error: Too many "
                             << "clocks for synchronous logic." << endl;
                        cerr << get_line() << ":      : Perhaps an"
                             << " asynchronous set/reset is misused?" << endl;
                        des->errors += 1;
                  }
                  pclk = tmp;

            } else {
                  events[event_idx++] = tmp;
            }
      }

      if (pclk == 0) {
            cerr << get_line() << ": error: None of the edges"
                 << " are valid clock inputs." << endl;
            cerr << get_line() << ":      : Perhaps the clock"
                 << " is read by a statement or expression?" << endl;
            return false;
      }

      connect(ff->pin_Clock(), pclk->pin(0));
      if (pclk->edge() == NetEvProbe::NEGEDGE) {
            perm_string polarity = perm_string::literal("Clock:LPM_Polarity");
            ff->attribute(polarity, verinum("INVERT"));

            if (debug_synth2) {
                  cerr << get_line() << ": debug: "
                       << "Detected a NEGEDGE clock for the synthesized ff."
                       << endl;
            }
      }

        /* Synthesize the input to the DFF. */
      bool flag = statement_->synth_sync(des, scope, ff,
                                         nex_map, nex_out, events);

      return flag;
}

/*
 * This method is called for a process that is determined to be
 * synchronous. Create a NetFF device to hold the output from the
 * statement, and synthesize that statement in place.
 */
bool NetProcTop::synth_sync(Design*des)
{
      if (debug_synth2) {
            cerr << get_line() << ": debug: "
                 << "Process is apparently synchronous. Making NetFFs."
                 << endl;
      }

      NexusSet nex_set;
      statement_->nex_output(nex_set);

        /* Make a model FF that will connect to the first item in the
           set, and will also take the initial connection of clocks
           and resets. */

      if (debug_synth2) {
            cerr << get_line() << ": debug: "
                 << "Top level making a "
                 << nex_set[0]->vector_width() << "-wide "
                 << "NetFF device." << endl;
      }

      NetFF*ff = new NetFF(scope(), scope()->local_symbol(),
                           nex_set[0]->vector_width());
      des->add_node(ff);
      ff->attribute(perm_string::literal("LPM_FFType"), verinum("DFF"));

      NetBus nex_d (scope(), nex_set.count());
      NetBus nex_q (scope(), nex_set.count());

        /* The Q of the NetFF devices is connected to the output that
           we are. The nex_q is a bundle of the outputs. We will also
           pass the nex_q as a map to the statement's synth_sync
           method to map it to the correct nex_d pin. */
      for (unsigned idx = 0 ;  idx < nex_set.count() ;  idx += 1) {
            connect(nex_set[idx], nex_q.pin(idx));
      }

        // Connect the input later.

        /* Synthesize the input to the DFF. */
      bool flag = statement_->synth_sync(des, scope(), ff,
                                         nex_q, nex_d,
                                         svector<NetEvProbe*>());
      if (! flag) {
            delete ff;
            return false;
      }


      NetNet*tmp = nex_d.pin(0).nexus()->pick_any_net();
      assert(tmp);

      tmp = crop_to_width(des, tmp, ff->width());
      connect(tmp->pin(0), ff->pin_Data());
      connect(nex_q.pin(0), ff->pin_Q());

      for (unsigned idx = 1 ;  idx < nex_set.count() ;  idx += 1) {
            NetFF*ff2 = new NetFF(scope(), scope()->local_symbol(),
                                  nex_set[idx]->vector_width());
            des->add_node(ff2);

            tmp = nex_d.pin(idx).nexus()->pick_any_net();
            assert(tmp);

            tmp = crop_to_width(des, tmp, ff2->width());

            connect(nex_q.pin(idx), ff2->pin_Q());
            connect(tmp->pin(0),    ff2->pin_Data());

            connect(ff->pin_Clock(), ff2->pin_Clock());
            if (ff->pin_Enable().is_linked())
                  connect(ff->pin_Enable(), ff2->pin_Enable());
            if (ff->pin_Aset().is_linked())
                  connect(ff->pin_Aset(), ff2->pin_Aset());
            if (ff->pin_Aclr().is_linked())
                  connect(ff->pin_Aclr(), ff2->pin_Aclr());
            if (ff->pin_Sset().is_linked())
                  connect(ff->pin_Sset(), ff2->pin_Sset());
            if (ff->pin_Sclr().is_linked())
                  connect(ff->pin_Sclr(), ff2->pin_Sclr());
      }

      return true;
}

class synth2_f  : public functor_t {

    public:
      void process(class Design*, class NetProcTop*);

    private:
};


/*
 * Look at a process. If it is asynchronous, then synthesize it as an
 * asynchronous process and delete the process itself for its gates.
 */
void synth2_f::process(class Design*des, class NetProcTop*top)
{
      if (top->attribute(perm_string::literal("ivl_synthesis_off")).as_ulong() != 0)
            return;

        /* If the scope that contains this process as a cell attribute
           attached to it, then skip synthesis. */
      if (top->scope()->attribute(perm_string::literal("ivl_synthesis_cell")).len() > 0)
            return;

      if (top->is_synchronous()) do {
            bool flag = top->synth_sync(des);
            if (! flag) {
                  cerr << top->get_line() << ": error: "
                       << "Unable to synthesize synchronous process." << endl;
                  des->errors += 1;
                  return;
            }
            des->delete_process(top);
            return;
      } while (0);

      if (! top->is_asynchronous()) {
            bool synth_error_flag = false;
            if (top->attribute(perm_string::literal("ivl_combinational")).as_ulong() != 0) {
                  cerr << top->get_line() << ": error: "
                       << "Process is marked combinational,"
                       << " but isn't really." << endl;
                  des->errors += 1;
                  synth_error_flag = true;
            }

            if (top->attribute(perm_string::literal("ivl_synthesis_on")).as_ulong() != 0) {
                  cerr << top->get_line() << ": error: "
                       << "Process is marked for synthesis,"
                       << " but I can't do it." << endl;
                  des->errors += 1;
                  synth_error_flag = true;
            }

            if (! synth_error_flag)
                  cerr << top->get_line() << ": warning: "
                       << "Process not synthesized." << endl;

            return;
      }

      if (! top->synth_async(des)) {
            cerr << top->get_line() << ": internal error: "
                 << "is_asynchronous does not match "
                 << "sync_async results." << endl;
            des->errors += 1;
            return;
      }

      des->delete_process(top);
}

void synth2(Design*des)
{
      synth2_f synth_obj;
      des->functor(&synth_obj);
}