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Adds two new functions to the ring buffer implementation, one to walk the ring by getting a pointer to the next element in the ring, and the other to Pop (remove) a specified element from somewhere in the ring and then move any elements up towards the head to fill the gap left. With these new functions in place, the Linux MS/TP datalink MSTP_Get_Reply() has been updated to walk the ring buffer to try to find the matching reply. If it is found then it is processed in the same way as usual, and then removed from the ring.

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When a packet is received which expects a reply a copy is stored in the PDU ring buffer so it can be matched with the reply. Unfortunately when the reply is received it is only checked against the first entry in the ring buffer. This can cause a failure if a second packet expecting a reply has been received while waiting for the first reply to arrive.
This is a known issue in the bacnet-stack open source stack, and there is a outstanding FIXME in the latest version of the source code:

        /* The ANSWER_DATA_REQUEST state is entered when a  */
        /* BACnet Data Expecting Reply, a Test_Request, or  */
        /* a proprietary frame that expects a reply is received. */
        /* FIXME: MSTP_Get_Reply waits for a matching reply, but
           if the next queued message doesn't match, then we
           sit here for Treply_delay doing nothing */

The fix for this is to check all the messages in the PDU queue to see if any of them match, and if one does then handle it in the normal way. Thank you to Ian Smith of Abelon Systems Ltd. for the patch!
This commit is contained in:
skarg
2017-06-25 18:06:27 +00:00
parent 7df0b9c5ed
commit 0b5a514cf7
3 changed files with 231 additions and 3 deletions
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bacnet-stack/ports/linux/dlmstp_linux.c
+17 -2
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@@ -581,7 +581,21 @@ uint16_t MSTP_Get_Reply(
mstp_port->DataLength, mstp_port->SourceAddress,
(uint8_t *) & pkt->buffer[0], pkt->length, pkt->destination_mac);
if (!matched) {
return 0;
/* Walk the rest of the ring buffer to see if we can find a match */
while (!matched &&
(pkt = (struct mstp_pdu_packet *)Ringbuf_Peek_Next(&poSharedData->PDU_Queue, (uint8_t *)pkt)) != NULL) {
matched =
dlmstp_compare_data_expecting_reply(&mstp_port->InputBuffer[0],
mstp_port->DataLength,
mstp_port->SourceAddress,
(uint8_t *) & pkt->buffer[0],
pkt->length,
pkt->destination_mac);
}
if (!matched) {
/* Still didn't find a match so just bail out */
return 0;
}
}
if (pkt->data_expecting_reply) {
frame_type = FRAME_TYPE_BACNET_DATA_EXPECTING_REPLY;
@@ -592,7 +606,8 @@ uint16_t MSTP_Get_Reply(
pdu_len = MSTP_Create_Frame(&mstp_port->OutputBuffer[0], /* <-- loading this */
mstp_port->OutputBufferSize, frame_type, pkt->destination_mac,
mstp_port->This_Station, (uint8_t *) & pkt->buffer[0], pkt->length);
(void) Ringbuf_Pop(&poSharedData->PDU_Queue, NULL);
/* This will pop the element no matter where we found it */
(void) Ringbuf_Pop_Element(&poSharedData->PDU_Queue, (uint8_t *)pkt, NULL);
return pdu_len;
}