The QSPI_LPBK_CLK is generated from the QSPIx_CLK and routed through the output buffer to a PMC MIO pin and returned back through the pin's input buffer to the controller for I/O delay compensation for greater timing accuracy. The I/O loopback clock signal is only used for I/O clocking >37.5 MHz. When the QSPIx_CLK device clock frequency is >37.5 MHz, the QSPI_LPBK_CLK must be routed to PMC MIO [6] and must be left unconnected on the PCB.