The data rate through the interface gearbox FIFOs must be constant during runtime of the RF-DAC tile, with no frequency drift between the PL clock and RF-DAC analog sample clock domains. If there is a frequency mismatch between these domains, a FIFO overflow can occur. The interface FIFOs have a built-in feature to determine if FIFO overflow has occurred, which is flagged to the PL through the IP interrupt mechanism.
There are two types of overflow: actual and marginal. Actual overflow indicates that the FIFO read/write pointers are overlapping, which means data is not being transferred safely between domains, and action must be taken. Marginal overflow is a warning and indicates that the FIFO read/write pointers are close to overlapping. Overflow should not occur during normal operation, and if overflow is seen it is an indication that the clocking infrastructure of the PL/PCB/IP core is incorrectly configured.