Add uwire support/functionality to the stub and vvp back ends

This patch adds a check in the vvp back end that a uwire has
at most one driver. Previously this was just converted (with
a warning message) to a wire just after elaboration.

ivl_target.h

@@ -353,7 +353,8 @@ typedef enum ivl_signal_type_e {
       IVL_SIT_TRI0 = 5,
       IVL_SIT_TRI1 = 6,
       IVL_SIT_TRIAND = 7,
-      IVL_SIT_TRIOR  = 8
+      IVL_SIT_TRIOR  = 8,
+      IVL_SIT_UWIRE  = 9
 } ivl_signal_type_t;
 
 /* This is the type code for ivl_statement_t objects. */

main.cc

@@ -1105,7 +1105,7 @@ int main(int argc, char*argv[])
       if (int emit_rc = des->emit(&dll_target_obj)) {
 	    if (emit_rc > 0) {
 		  cerr << "error: Code generation had "
-		       << emit_rc << " errors."
+		       << emit_rc << " error(s)."
 		       << endl;
 		  return 1;
 	    }

t-dll.cc

@@ -2384,10 +2384,12 @@ void dll_target::signal(const NetNet*net)
 	    assert(0);
 	    break;
 
+	      /* We will convert this to a TRI after we check that there
+		 is only one driver. */
 	  case NetNet::UWIRE:
-	    cerr << net->get_fileline()
-	         << ": warning: uwire is not currently supported, converting "
-	            "it to a wire!" << endl;
+	    obj->type_ = IVL_SIT_UWIRE;
+	    break;
+
 	  case NetNet::TRI:
 	  case NetNet::WIRE:
 	  case NetNet::IMPLICIT:

tgt-stub/stub.c

@@ -1224,6 +1224,9 @@ static void show_signal(ivl_signal_t net)
 	  case IVL_SIT_TRI1:
 	    type = "tri1";
 	    break;
+	  case IVL_SIT_UWIRE:
+	    type = "uwire";
+	    break;
 	  default:
 	    break;
       }

tgt-vvp/draw_net_input.c

@@ -47,6 +47,7 @@ static ivl_signal_type_t signal_type_of_nexus(ivl_nexus_t nex)
 		  continue;
 	    if (stype == IVL_SIT_NONE)
 		  continue;
+	    if (stype == IVL_SIT_UWIRE) return IVL_SIT_UWIRE;
 	    out = stype;
       }
 
@@ -572,6 +573,7 @@ static void draw_net_input_x(ivl_nexus_t nex,
       res = signal_type_of_nexus(nex);
       switch (res) {
 	  case IVL_SIT_TRI:
+	  case IVL_SIT_UWIRE:
 	    resolv_type = "tri";
 	    break;
 	  case IVL_SIT_TRI0:
@@ -660,6 +662,7 @@ static void draw_net_input_x(ivl_nexus_t nex,
 		  tmp += strlen(tmp);
 		  switch (res) {
 		      case IVL_SIT_TRI:
+		      case IVL_SIT_UWIRE:
 			for (jdx = 0 ;  jdx < wid ;  jdx += 1)
 			      *tmp++ = 'z';
 			break;
@@ -698,6 +701,28 @@ static void draw_net_input_x(ivl_nexus_t nex,
 	    return;
       }
 
+	/* A uwire is a tri with only one driver. */
+      if (res == IVL_SIT_UWIRE) {
+	    if (ndrivers > 1) {
+		  unsigned uidx;
+		  ivl_signal_t usig;
+		    /* Find the uwire signal. */
+		  for (uidx = 0 ;  uidx < ivl_nexus_ptrs(nex) ;  uidx += 1) {
+			ivl_nexus_ptr_t ptr = ivl_nexus_ptr(nex, uidx);
+			usig = ivl_nexus_ptr_sig(ptr);
+			if (usig != 0) break;
+		  }
+		  assert(usig);
+
+		  fprintf(stderr, "%s:%u: vvp.tgt error: uwire \"%s\" must "
+		                  "have a single driver, found (%u).\n",
+		                  ivl_signal_file(usig),
+		                  ivl_signal_lineno(usig),
+		                  ivl_signal_basename(usig), ndrivers);
+		  vvp_errors += 1;
+	    }
+	    res = IVL_SIT_TRI;
+      }
 
 	/* If the nexus has exactly one driver, then simply draw
 	   it. Note that this will *not* work if the nexus is not a