Second cyphal message not accepted

Applications & Usage Libcanard
1

Hello,

I am running CAN communication between two nodes, A to B, using cyphal and libcanard C libraries, on STM32 u585. B is subscribed for serving 3 services on port IDs: 435, 121 and 220, in this order.

I am trying to send several messages #435 (only one frame, size 4 bytes) from A to B. The first one is received correctly and accepted by canardRxAccept(). When the second message comes, the canardRxAccept() fails in cavlSearch() - it fails in CAVL_ASSERT((NULL == *n) || ((*n)->up == up)) macro. The strange thing is that if I comment out this macro, any number of messages is accepted and handled.

I tried to dig into the problem and compared difference in the first and the second message, in evaluating the macro. If I name the conditions in the macro as c1 and c2 then the first message conditions are false true while the second false false.
Going deeper, c2 defined as L == R, for the first message L= last_subscription, R=last_subscription, while for the second message L= first subscription, R=last_subscription.

Another observation - if I remove either #121 or #220 subscription then everything works correctly as expected.

Do you have any idea:

  • why the first and the second message are processed differently
  • if I disable the macro all messages are processed correctly?

I guess it’s some memory problem? The cavlSearch() is for some reason “lost”.

Thanx.
Best regards,
peter

2

You have a memory corruption. It could be caused by dangling pointers, stack overflow, race conditions, etc.

3

Hi Pavel,

thanx for a prompt reply. That is what I also suspect. After all the subscriptions are made, should the base tree be constant through the all subscriptions?

Thanx.
Best regards,
peter

4

The topology of the tree will not be altered unless you add or remove subscriptions. The node states, however, will be altered as the library serves incoming traffic.