Why do I get the error message "Error: Differential I/O output pin "<name>" is assigned to a non differential location "<name>"

Description

Due to a bug in Quartus® II 10.1sp1 and previous versions, if you regenerate the PCI Express® core from x1 lane to multiple lanes such as x4 or x8, software may not update the <variant>_serdes.v(.vhd) file. As a result, some of the upper lanes are not connected to transceiver Physical Channels, and fitter will error out with messages similar to the following:

• Error: Differential I/O output pin pcie_tx1_o_pin is assigned to a non differential location P2. However, it must be assigned to a differential input location File: <path/file_name>
• Error: Differential I/O input pin pcie_rx1_i_pin is assigned to a non differential location T2. However, it must be assigned to a differential input location File: <path/file_name>

To workaround the issue, delete <variant>_serdes.v(.vhd) file from your working directory and regenerate the core.

This problem will be fixed in a future version of the Quartus II software.

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