What might be the causes of "ESPCONN_IF" error?

[YimingLi]

Hi Espressif,

What might be the causes of "ESPCONN_IF" returned by espconn_sendto() to send UDP data, and how to fix it or handle it?

sdk: 1.5.4 NON-OS

Here below is the reproduction scenario:

1. We call espconn_sendto() to continuously send udp packet of 1024 bytes as below:
(1) espconn_sendto() to send a packet of 1024 bytes to an existing ip address of the same LAN;
(2) wait espconn_sent_callback() called, or wait more than 1ms using timer
(3) go to (1) to repeat

2. However, we found via debug info that, we could repeat only tens of times, then the espconn_sent_callback() will not
be called and no data will be sent out, while espconn_sendto() will return -14, that is "ESPCONN_IF" error.

3. The first tens of packets in 1024 bytes each have been sent out succesfully and received by the UDP peer successfully.

4. If we call espconn_sendto() sending to a "fake" (not present) ip addiress, the espconn_sendto() always return successfully,
no "ESPCONN_IF" error will returned.

What makes differences here between 2 and 4?

5. If we give some delay after every 8 packets have been sent out as above 1, then there will be no "ESPCONN_IF" error as well.
However, this slowdown the throughout we don't expected.

Would you please kindly give us some hints to fix it here?

Thanks in advance!

Yiming Li

[YimingLi]

Can Anyone give some hints here?!

Thanks

Yiming