Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/Series1/EFM32PG12B/EFM32PG12B500F1024IL125/ETM/ETMFFLR#0x0
ETM Fifo Full Level Register
Bytes left in FIFO
https://github.com/cmsis-svd/cmsis-svd-data