In PCI Express x4 core v3.3, when do we need to set VCO auto-band options in the auto-configure text file? In pcs_pipe_8b_4x.txt, the last two options vco_reg_band_sel and vco_auto_band_enb are commented out.
auto-ge中的最后两个设置nerated pcs_pipe_8b_4x.txt of PCIe x4 core (v3.3) are VCO auto-band options. They must be used only for Lattice Standard PCIe Evaluation Board containing ECP2M35.
The Lattice Standard Evaluation Board supports both 50 and 35 device (672 BGA package). In the 35 device package, the VCC_serdes of the missing quad is shorted
to VCC_core. If the VCC_serdes for the missing quad is not connected on the board, there is no issue. The Eval board supported both devices so the VCC_serdes of the 2 quads are connected together.
The option in the text file is to turn off the autoband feature of the Serdes PLL, forcing it to work based on a pre-determined frequency band to work around the
short issue mentioned.
A PCIe design using ECP2M35-672BGA should NOT connect VCC_Serdes for the missing quad and ignore the auto-band option in the .txt file.