We design a custom carrier board ，in which we reference the NVIDIA carrier board and only keep two parts of the main functions:
2.Ethernet(same PHY 88E1512)
The issue is that all boards PCIe function are OK, but the Ethernet have some problem.Some boards can work normally,but some can not work, the MAC controller can not attach to PHY, and the GPU boot log [b]display error 19.
We measure the waveform of the abnormal and normal boards MDIO/MDC signal，The difference of the two Waveform is the MDIO signal .(Why the MDC is not stable output?)
We measure the peripheral circuit of PHY 88E1512, it is seem OK. And we use the module of 88E1512 to connect to some kinds of FPGA , the Ethernet are OK.