diff --git a/vvp/compile.cc b/vvp/compile.cc
index f87aa32a8..508e2d14a 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -1197,6 +1197,9 @@ void compile_resolver(char*label, char*type, unsigned argc, struct symb_s*argv)
       if (strcmp(type,"tri") == 0) {
 	    obj = new resolv_functor(vvp_scalar_t(BIT4_Z, 0));
 
+      } else if (strncmp(type,"tri$",4) == 0) {
+	    obj = new resolv_functor(vvp_scalar_t(BIT4_Z, 0), strdup(type+4));
+
       } else if (strcmp(type,"tri0") == 0) {
 	    obj = new resolv_functor(vvp_scalar_t(BIT4_0, 5));
 
diff --git a/vvp/compile.h b/vvp/compile.h
index ae6c90ab9..c5aaab4de 100644
--- a/vvp/compile.h
+++ b/vvp/compile.h
@@ -23,6 +23,7 @@
 #endif
 
 # include  <stdio.h>
+# include  <fstream>
 # include  "parse_misc.h"
 # include  "vpi_user.h"
 # include  "vvp_net.h"
@@ -44,6 +45,12 @@ extern void compile_cleanup(void);
 
 extern bool verbose_flag;
 
+/*
+ * If this file opened, then write debug information to this
+ * file. This is used for debugging the VVP runtime itself.
+ */
+extern ofstream debug_file;
+
 /*
  *  Connect a list of symbols to a contiguous set of ipoints.
  *  Constants C<?> are handled by setting the ival of the ipoint.
diff --git a/vvp/debug.txt b/vvp/debug.txt
new file mode 100644
index 000000000..0a2e405cc
--- /dev/null
+++ b/vvp/debug.txt
@@ -0,0 +1,18 @@
+
+DEBUG AIDS FOR VVP
+
+Debuging vvp can be fiendishly difficult, so there are some built in
+debugging aids. These are enabled by setting the environment variable
+VVP_DEBUG to the path to an output file. Then, various detailed debug
+tools can be enabled as described below.
+
+* .resolv
+
+The .resolv can print debug information along with a label by
+specifying the debug output label on the .resolv line:
+
+   .resolv tri$<label>
+
+In this case, the "$" character directly after the "tri" enables debug
+dumps for this node, and the <label> is the label to prepend to log
+messages from this node.
diff --git a/vvp/main.cc b/vvp/main.cc
index 408b2c7de..5bf72a593 100644
--- a/vvp/main.cc
+++ b/vvp/main.cc
@@ -47,6 +47,8 @@
 # include  <windows.h>
 #endif
 
+ofstream debug_file;
+
 #if defined(__MINGW32__) && !defined(HAVE_GETOPT_H)
 extern "C" int getopt(int argc, char*argv[], const char*fmt);
 extern "C" int optind;
@@ -205,6 +207,13 @@ int main(int argc, char*argv[])
 	    return -1;
       }
 
+	/* If the VVP_DEBUG variable is set, then it contains the path
+	   to the vvp debug file. Open it for output. */
+
+      if (char*path = getenv("VVP_DEBUG")) {
+	    debug_file.open(path, ios_base::out);
+      }
+
       design_path = argv[optind];
 
 	/* This is needed to get the MCD I/O routines ready for
diff --git a/vvp/resolv.cc b/vvp/resolv.cc
index a65ccb96d..5bf36ff28 100644
--- a/vvp/resolv.cc
+++ b/vvp/resolv.cc
@@ -22,13 +22,14 @@
 
 # include  "resolv.h"
 # include  "schedule.h"
+# include  "compile.h"
 # include  "statistics.h"
 # include  <iostream>
 # include  <assert.h>
 
 
-resolv_functor::resolv_functor(vvp_scalar_t hiz_value)
-: hiz_(hiz_value)
+resolv_functor::resolv_functor(vvp_scalar_t hiz_value, const char*debug_l)
+: hiz_(hiz_value), debug_label_(debug_l)
 {
 }
 
@@ -72,11 +73,10 @@ void resolv_functor::recv_vec8(vvp_net_ptr_t port, vvp_vector8_t bit)
       vvp_vector8_t out (bit);
 
       for (unsigned idx = 0 ;  idx < 4 ;  idx += 1) {
-	    if (val_[idx].size() == 0)
-		  continue;
 	    if (idx == pdx)
 		  continue;
-
+	    if (val_[idx].size() == 0)
+		  continue;
 	    out = resolve(out, val_[idx]);
       }
 
@@ -87,43 +87,17 @@ void resolv_functor::recv_vec8(vvp_net_ptr_t port, vvp_vector8_t bit)
 	    }
       }
 
+      if (debug_label_ && debug_file.is_open())
+	    debug_file << "[" << schedule_simtime() << "] "
+		       << debug_label_ << ": Resolv out=" << out
+		       << " in=" << val_[0] << ", " << val_[1]
+		       << ", " << val_[2] << ", " << val_[3] << endl;
+
       vvp_send_vec8(ptr->out, out);
 }
 
 
 /*
  * $Log: resolv.cc,v $
- * Revision 1.26  2005/06/22 18:30:12  steve
- *  Inline more simple stuff, and more vector4_t by const reference for performance.
- *
- * Revision 1.25  2005/06/22 00:04:49  steve
- *  Reduce vvp_vector4 copies by using const references.
- *
- * Revision 1.24  2005/06/15 00:47:15  steve
- *  Resolv do not propogate inputs that do not change.
- *
- * Revision 1.23  2005/04/13 06:34:20  steve
- *  Add vvp driver functor for logic outputs,
- *  Add ostream output operators for debugging.
- *
- * Revision 1.22  2005/03/12 04:27:43  steve
- *  Implement VPI access to signal strengths,
- *  Fix resolution of ambiguous drive pairs,
- *  Fix spelling of scalar.
- *
- * Revision 1.21  2005/02/13 05:26:30  steve
- *  tri0 and tri1 resolvers must replace HiZ with 0/1 after resolution.
- *
- * Revision 1.20  2005/01/09 20:11:16  steve
- *  Add the .part/pv node and related functionality.
- *
- * Revision 1.19  2004/12/31 06:00:06  steve
- *  Implement .resolv functors, and stub signals recv_vec8 method.
- *
- * Revision 1.18  2004/12/11 02:31:30  steve
- *  Rework of internals to carry vectors through nexus instead
- *  of single bits. Make the ivl, tgt-vvp and vvp initial changes
- *  down this path.
- *
  */
 
diff --git a/vvp/resolv.h b/vvp/resolv.h
index 7fea803d4..4896ed65c 100644
--- a/vvp/resolv.h
+++ b/vvp/resolv.h
@@ -40,7 +40,7 @@
 class resolv_functor : public vvp_net_fun_t {
 
     public:
-      explicit resolv_functor(vvp_scalar_t hiz_value);
+      explicit resolv_functor(vvp_scalar_t hiz_value, const char* debug =0);
       ~resolv_functor();
 
       void recv_vec4(vvp_net_ptr_t port, const vvp_vector4_t&bit);
@@ -51,7 +51,10 @@ class resolv_functor : public vvp_net_fun_t {
 
     private:
       vvp_vector8_t val_[4];
+	// Bit value to emit for HiZ bits.
       vvp_scalar_t hiz_;
+	// True if debugging is enabled
+      const char* debug_label_;
 };
 
 /*