diff --git a/comm/messages.c b/comm/messages.c
index 7ce00ea..7eda1fa 100644
--- a/comm/messages.c
+++ b/comm/messages.c
@@ -6,40 +6,24 @@
 #include "TinyFrame.h"
 #include "framework/unit_registry.h"
 #include "comm/messages.h"
-#include "task_sched.h"
 
-TinyFrame tf_;
+static TinyFrame tf_;
 TinyFrame *comm = &tf_;
 
 // ---------------------------------------------------------------------------
 
-// Pre-declaring local functions
-static TF_Result lst_ping(TinyFrame *tf, TF_Msg *msg);
-static TF_Result lst_unit(TinyFrame *tf, TF_Msg *msg);
-static TF_Result lst_list_units(TinyFrame *tf, TF_Msg *msg);
-static TF_Result lst_default(TinyFrame *tf, TF_Msg *msg);
-
-void comm_init(void)
-{
-    TF_InitStatic(comm, TF_SLAVE);
-    TF_AddTypeListener(comm, MSG_PING, lst_ping);
-    TF_AddTypeListener(comm, MSG_UNIT_REQUEST, lst_unit);
-    TF_AddTypeListener(comm, MSG_LIST_UNITS, lst_list_units);
-
-    // fall-through
-    TF_AddGenericListener(comm, lst_default);
-}
-
-// ---------------------------------------------------------------------------
-
+/**
+ * Ping request listener - returns version string and other info about the build
+ */
 static TF_Result lst_ping(TinyFrame *tf, TF_Msg *msg)
 {
     com_respond_snprintf(msg->frame_id, MSG_SUCCESS, "%s/%s", GEX_VERSION, GEX_PLATFORM);
     return TF_STAY;
 }
 
-// ----------------------------------------------------------------------------
-
+/**
+ * Default listener, fallback for unhandled messages
+ */
 static TF_Result lst_default(TinyFrame *tf, TF_Msg *msg)
 {
     dbg("!! Unhandled msg type %02"PRIx8", frame_id 0x%04"PRIx16, msg->type, msg->frame_id);
@@ -48,18 +32,31 @@ static TF_Result lst_default(TinyFrame *tf, TF_Msg *msg)
     return TF_STAY;
 }
 
-// ----------------------------------------------------------------------------
-
+/**
+ * Unit request listener, a message targeted at a particular
+ */
 static TF_Result lst_unit(TinyFrame *tf, TF_Msg *msg)
 {
     ureg_deliver_unit_request(msg);
     return TF_STAY;
 }
 
-// ----------------------------------------------------------------------------
 
 static TF_Result lst_list_units(TinyFrame *tf, TF_Msg *msg)
 {
     ureg_report_active_units(msg->frame_id);
     return TF_STAY;
 }
+
+// ---------------------------------------------------------------------------
+
+void comm_init(void)
+{
+    TF_InitStatic(comm, TF_SLAVE);
+    TF_AddTypeListener(comm, MSG_PING, lst_ping);
+    TF_AddTypeListener(comm, MSG_UNIT_REQUEST, lst_unit);
+    TF_AddTypeListener(comm, MSG_LIST_UNITS, lst_list_units);
+
+    // fall-through
+    TF_AddGenericListener(comm, lst_default);
+}
diff --git a/framework/unit_registry.c b/framework/unit_registry.c
index 524b2f9..d6cf730 100644
--- a/framework/unit_registry.c
+++ b/framework/unit_registry.c
@@ -516,8 +516,11 @@ void ureg_deliver_unit_request(TF_Msg *msg)
     UlistEntry *li = ulist_head;
     while (li != NULL) {
         Unit *const pUnit = &li->unit;
-        if (pUnit->callsign == callsign) {
+        if (pUnit->callsign == callsign && pUnit->status == E_SUCCESS) {
             bool ok = pUnit->driver->handleRequest(pUnit, msg->frame_id, command, &pp);
+
+            // send extra SUCCESS confirmation message.
+            // error is expected to have already been reported.
             if (ok && confirmed) {
                 com_respond_ok(msg->frame_id);
             }
@@ -530,7 +533,7 @@ void ureg_deliver_unit_request(TF_Msg *msg)
     com_respond_snprintf(msg->frame_id, MSG_ERROR, "NO UNIT @ %"PRIu8, callsign);
 }
 
-
+/** Send a response for a unit-list request */
 void ureg_report_active_units(TF_ID frame_id)
 {
     // count bytes needed
@@ -539,24 +542,29 @@ void ureg_report_active_units(TF_ID frame_id)
     UlistEntry *li = ulist_head;
     uint32_t count = 0;
     while (li != NULL) {
-        count++;
-        msglen += strlen(li->unit.name)+1;
+        if (li->unit.status == E_SUCCESS) {
+            count++;
+            msglen += strlen(li->unit.name) + 1;
+            msglen += strlen(li->unit.driver->name) + 1;
+        }
         li = li->next;
     }
-    msglen += count;
+    msglen += count; // one byte per message for the callsign
 
     bool suc = true;
     uint8_t *buff = malloc_ck(msglen, &suc);
     if (!suc) { com_respond_str(MSG_ERROR, frame_id, "OUT OF MEMORY"); return; }
-
     {
         PayloadBuilder pb = pb_start(buff, msglen, NULL);
         pb_u8(&pb, (uint8_t) count); // assume we don't have more than 255 units
 
         li = ulist_head;
         while (li != NULL) {
-            pb_u8(&pb, li->unit.callsign);
-            pb_string(&pb, li->unit.name);
+            if (li->unit.status == E_SUCCESS) {
+                pb_u8(&pb, li->unit.callsign);
+                pb_string(&pb, li->unit.name);
+                pb_string(&pb, li->unit.driver->name);
+            }
             li = li->next;
         }
 
@@ -564,6 +572,5 @@ void ureg_report_active_units(TF_ID frame_id)
 
         com_respond_buf(frame_id, MSG_SUCCESS, buff, msglen);
     }
-
     free(buff);
 }