Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/Series1/EFM32GG12B/EFM32GG12B530F512GQ100/USART4/RXDOUBLE#0x0
RX FIFO Double Data Register
RX Data 0
RX Data 1
https://github.com/cmsis-svd/cmsis-svd-data