Hello Matti,
Yes you are right, you need to change this setting in the ENET_default_params[] structure which is located in the file init_enet.c. In that structure change the second element from "Auto_Negotiate" to "Half_Duplex_10M" or "Full_Duplex_10M", "Half_Duplex_100M" or "Full_Duplex_100M". After these changes you need to Rebuild the BSP, PSP and RTCS libraries.

Have a great day,
Sol
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