STM32H5 HAL_ETH_Transmit_IT() causes tcp retransmissions in ST example

[sssooo]

Hi all,

during testing a custom project with NETXDUO on NUCLEO-H563ZI I've noticed that sometimes web server response is rather slow.

Wireshark shows rather frequent TCP retransmissions and other problems.

To be sure, I've tried an example from ST (Nx_Iperf) with the same result.

It seems that problem is in ETH_Prepare_Tx_Descriptors(), in check of Tx Descriptor:

  /* Current Tx Descriptor Owned by DMA: cannot be used by the application  */
  if ((READ_BIT(dmatxdesc->DESC3, ETH_DMATXNDESCWBF_OWN) == ETH_DMATXNDESCWBF_OWN)
      || (dmatxdesclist->PacketAddress[descidx] != NULL))
  {
    return HAL_ETH_ERROR_BUSY;
  }

I removed this check and TCP retransmissions became much less frequent.
Is there a better solution?

[ASEHST]

Hello @sssooo,

Thank you for your reply,

The Owned Tx Descriptor check indicates that a packet is already associated with the descriptor, making it unavailable for reuse by the application. This check ensures that the application does not modify or use a descriptor currently being processed by the DMA or linked to an unprocessed packet.

Although removing this check might improve performance, it may not be a sustainable solution and risks data corruption.

We are analyzing the root cause of these retransmissions internally and will keep you updated.

With Regards,