Re: [lwip-users] TCP Retransmission when receiving consecutive packets

[Julien Jemine]

Hi Sergio,

I've found this drop packet thing in my driver, however it doesn't seem to break there.

I've had a look at the driver code but I can't find anything...

I am a bit surprised that the ethernet interrupt just raises a flag :

static void eth_notify (ARM_ETH_MAC_EVENT event) {

  /* Send notification on RX event */

  if (event == ARM_ETH_MAC_EVENT_RX_FRAME) {

    rx_event = true;

  }

}

It seems to imply that calling ethernetif_poll in an IDLE thread will only process on packet even if multiple interrupts have been raised :

void ethernetif_poll (struct netif *netif) {

  struct ethernetif *eth = netif->state;

  if (!eth->phy_ok || eth->link == ARM_ETH_LINK_DOWN) {

    return;

  }

  if (rx_event) {

    rx_event = false;

    /* process received ethernet packet */

    ethernetif_input (netif);

  }

}

I think that an atomic counter and a while loop instead of a flag and a "if" would be more appropriate. Am I wrong ? 

Could that have anything to do with my problem ?

Thanks for your help,

Julien.

2014-03-20 15:10 GMT+01:00 Sergio R. Caprile <address@hidden>:

Hi Julien.
Yes, there is a TCP retransmission from your host.
I bet that is because when the two packets come in such a close
proximity your Ethernet driver is losing the second one. This, in fact,
can be because there is a problem with the driver itself, or you have a
really low-memory condition and the driver can't find enough memory to
store the packet.
If I would have to hunt this witch, I would start by setting a
breakpoint on the Ethernet driver low_level_input() routine, somewhere
around here:


static struct pbuf *
low_level_input(struct netif *netif)
{
  [...]
  /* We allocate a pbuf chain of pbufs from the pool. */
  p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL);

  if (p != NULL) {
        [...]
      read data into(q->payload, q->len);
    }
    acknowledge that packet has been read();
  [...]
  } else {
    drop packet();      <-------------

It actually depends on how the one who actually wrote the driver wanted
to make it difficult for you.
Let me know how it goes.
Cheers

--

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