Error (18108): Can't place multiple pins assigned to pin location <CLKUSR pin number> (IOPAD_<CLKUSR pin location address>) - Error (18108): Can't place multiple pins assigned to pin location <CLKUSR pin number> (IOPAD_<CLKUSR pin location address>) Description Due to a problem in the Intel® Quartus® Prime Software version 15.1 and later, you might see the following error message when compiling designs targeting Intel® Arria® 10 devices. Error (18108): Can't place multiple pins assigned to pin location <CLKUSR pin number> (IOPAD_<CLKUSR pin location address>) Info (18109): Pin ~ALTERA_CLKUSR~ is assigned to pin location <CLKUSR pin number> (IOPAD_<CLKUSR pin location address>) Info (18109): Pin <a differential pin name>(n) is assigned to pin location <CLKUSR pin number> (IOPAD_<CLKUSR pin location address>) Although you can use CLKUSR pin as a user I/O pin when CLKUSR is not optionally used for device configuration, initialization, transceiver calibration or/and EMIF HMC calibration, this error might occur if an n-channel of a differential pin pair is assigned to the dual purpose CLKUSR pin. Resolution To avoid this error, use the following assignment: set_global_assignment -name AUTO_RESERVE_CLKUSR_FOR_CALIBRATION OFF Related Articles Error (14566): The Fitter cannot place 1 periphery component(s) due to conflicts with existing constraints (1 I/O pad(s)) Error (17950): Pin corresponding to CLKUSR has not been reserved in the device. Cannot perform unused RX clock workaround. Custom Fields values: ['novalue'] Troubleshooting FB: 500565; False ['novalue'] ['FPGA Dev Tools Quartus® Prime Software Pro', 'FPGA Dev Tools Quartus® Prime Software Standard'] novalue 15.1 ['Arria® 10 FPGAs and SoCs'] ['novalue'] ['novalue'] ['novalue']