47.7.11.3 Receiving Data with FIFO Enabled
When the Receive FIFO is enabled, FLEX_US_RHR access reads the FIFO.
When data are present in the Receive FIFO (RXRDY flag set to ‘1’), the exact number of data can be checked with FLEX_US_FLR.RXFL. All the data can be read successively in FLEX_US_RHR without checking the RXRDY flag between each access.