Feature/zeroing rx buffer remain (#90)

* Added zeroing rx buffer remain

* Added zeroing rx buffer remain

* Added safety margin for the rx-buffer in the different ports.

* Added safety margin for the receive buffer.

* Added DoxyGen comments.

* Fixed checking return value when calculating distance between opening and closing tag on multiple properties.

ports/bdk-atxx4-mstp/bacnet.c

@@ -141,7 +141,17 @@ void bacnet_init(void)
     Send_I_Am(&Handler_Transmit_Buffer[0]);
 }
 
-static uint8_t PDUBuffer[MAX_MPDU];
+/** Static receive buffer, initialized with zeros by the C Library Startup Code. */
+
+static uint8_t PDUBuffer[MAX_MPDU + 16 /* Add a little safety margin to the buffer,
+                                        * so that in the rare case, the message
+                                        * would be filled up to MAX_MPDU and some
+                                        * decoding functions would overrun, these
+                                        * decoding functions will just end up in
+                                        * a safe field of static zeros. */];
+
+/** BACnet task doing receive and transmit. */
+
 void bacnet_task(void)
 {
     uint8_t mstp_mac_address;
@@ -208,7 +218,7 @@ void bacnet_task(void)
         dcc_timer_seconds(DCC_CYCLE_SECONDS);
     }
     /* handle the messaging */
-    pdu_len = datalink_receive(&src, &PDUBuffer[0], sizeof(PDUBuffer), 0);
+    pdu_len = datalink_receive(&src, &PDUBuffer[0], MAX_MPDU, 0);
     if (pdu_len) {
         npdu_handler(&src, &PDUBuffer[0], pdu_len);
     }