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[r3137] 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:
Steve Karg
2017-06-25 20:06:27 +02:00
committed by Patrick Grimm
parent 92d9ec7340
commit 17058b23b3
3 changed files with 231 additions and 3 deletions
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5
include/ringbuf.h
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@@ -63,6 +63,9 @@ extern "C" {
volatile uint8_t *Ringbuf_Peek(RING_BUFFER const *b);
bool Ringbuf_Pop(RING_BUFFER * b,
uint8_t * data_element);
bool Ringbuf_Pop_Element(RING_BUFFER * b,
uint8_t * this_element,
uint8_t * data_element);
bool Ringbuf_Put_Front(RING_BUFFER * b,
uint8_t * data_element);
/* head */
@@ -70,6 +73,8 @@ extern "C" {
uint8_t * data_element);
/* pair of functions to use head memory directly */
volatile uint8_t *Ringbuf_Data_Peek(RING_BUFFER * b);
volatile uint8_t *Ringbuf_Peek_Next(RING_BUFFER const *b,
uint8_t * data_element);
bool Ringbuf_Data_Put(RING_BUFFER * b, volatile uint8_t *data_element);
/* Note: element_count must be a power of two */
bool Ringbuf_Init(RING_BUFFER * b,