Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/SiM3_NRND/SIM3L168_A/UART_0/CLKDIV#0x0
CLKDIV=DIV1
Clock Divider
Clock Divider.
0 (DIV1): Divide by 1.
1 (DIV2): Divide by 2.
2 (DIV4): Divide by 4.
https://github.com/cmsis-svd/cmsis-svd-data