Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/SiM3_NRND/SIM3C167_B/RSTSRC_0/CONFIG#0x0
PMSEL=PM9_DIS
Configuration Options
Power Mode Select.
0 (PM9_DIS): Power Mode < PM9.
1 (PM9_EN): Power Mode = PM9.
https://github.com/cmsis-svd/cmsis-svd-data