ENET_TCR_FDEN
tcr |= ENET_TCR_FDEN; /* full duplex */
tcr &= ~ENET_TCR_FDEN; /* half duplex */
if ((tcr ^ tcr0) & ENET_TCR_FDEN) {
ENET_REG_WRITE(sc, ENET_TCR, fulldup ? ENET_TCR_FDEN : 0);