This parameter can be one of the following values: SPI_RXFIFO_THRESHOLD or SPI_RXFIFO_THRESHOLD_QF : RXNE event is generated if the FIFO level is greater or equal to 1/4(8-bits). SPI_RXFIFO_THRESHOLD_HF: RXNE event is generated if the FIFO level is greater or equal to 1/2(16 bits).