cr1
uint8_t cr0, cr1, fc;
cr1 = CSR_READ_1(sc, VR_CR1);
mfdx = (cr1 & VR_CR1_FULLDUPLEX) != 0;
cr1 |= VR_CR1_FULLDUPLEX;
cr1 &= ~VR_CR1_FULLDUPLEX;
CSR_WRITE_1(sc, VR_CR1, cr1);