Instead using iperf3, I have tried iperf as a server on the computer side and sending UDP packets from W5100S-EVB-PICO. It worked for me, but I could claim only 8-9MBit/s… I started another post ([W5100S-EVB-Pico]: How to set PHY_SPEED to 100Mbit/s ?) dealing with setting the board to 100MBit/s.
This post can be marked as “solved”.
