Provided a feedback path, so we can find out if our foreign device registration has been NAK'd.

bacnet-stack/demo/handler/dlenv.c

@@ -79,12 +79,19 @@ void dlenv_bbmd_ttl_set( int ttl_secs )
 }
 
 /** Get the result of the last attempt to register with the indicated BBMD.
+ * If we sent a foreign registration request, then see if we've received 
+ * a NAK in our BVLC handler.
+ * 
  * @return Positive number (of bytes sent) if registration was successful,
  *         0 if no registration request was made, or
  *         -1 if registration attempt failed.
  */
 int dlenv_bbmd_result( void )
 {
+    if ( (bbmd_result > 0) && 
+         (bvlc_get_last_result() == BVLC_RESULT_REGISTER_FOREIGN_DEVICE_NAK) ) 
+        return -1;
+    /* Else, show our send: */
     return bbmd_result;
 }
 #endif

bacnet-stack/include/bvlc.h

@@ -101,6 +101,11 @@ struct sockaddr_in;     /* Defined elsewhere, needed here. */
             uint8_t * npdu,     
             uint16_t received_bytes);
 
+    /** Returns the last BVLL Result we received, either as the result of a BBMD
+     * request we sent, or (if not a BBMD or Client), from trying to register 
+     * as a foreign device. */
+    BACNET_BVLC_RESULT bvlc_get_last_result();
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */

bacnet-stack/src/bvlc.c

@@ -883,7 +883,7 @@ uint16_t bvlc_receive(
                Foreign-Device message. At the expiration of the timer, the
                foreign device shall re-register with the BBMD by sending a BVLL
                Register-Foreign-Device message */
-            /* FIXME: clients may need this result */
+            /* Clients can now get this result */
             (void) decode_unsigned16(&npdu[4], &result_code);
             BVLC_Result_Code = (BACNET_BVLC_RESULT) result_code;
             debug_printf("BVLC: Result Code=%d\n", BVLC_Result_Code);
@@ -1286,6 +1286,19 @@ void bvlc_for_non_bbmd(
     }
 }
 
+/** Returns the last BVLL Result we received, either as the result of a BBMD
+ * request we sent, or (if not a BBMD or Client), from trying to register 
+ * as a foreign device.
+ * 
+ * @return BVLC_RESULT_SUCCESSFUL_COMPLETION on success,
+ * BVLC_RESULT_REGISTER_FOREIGN_DEVICE_NAK if registration failed,
+ * or one of the other codes (if we are a BBMD).
+ */
+BACNET_BVLC_RESULT bvlc_get_last_result()
+{
+    return BVLC_Result_Code;
+}
+
 #ifdef TEST
 #include <assert.h>
 #include <string.h>