ARP response but no ACK from TCP server (stm32f4+freertos+lwip)
I'm implementing a TCP/HTTP server on a custom board with a LAN8710A PHY. The board is connected to a PC via an ethernet cable with static IP assigned on both sides. I'm stuck at Netconn_accept() (when I enable LWIP_SO_RCVTIMEO I see that Netconn_accept times out). On Wireshark I can see ARP request from the PC and the correct ARP response from STM. I also see a SYN request from the PC, followed by TCP retransmissions of SYN, but STM never responds back with an ACK. I don't know for sure if the ACK request ever gets to STM. Unfortunately I haven't been able to get USB_OTG to work either so I can't see any LWIP debug messages other than setting breakpoints.
I know this is not a new issue from all the online discussions I've come across, and it is a mystery to me why some get it to work and many don't, following essentially the STM examples. I'm hoping someone skilled with the art can give me some pointers given the symptoms I described above.