Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/Series1/EFR32ZG13P/EFR32ZG13P531F512GM48/ETM/ETMFFLR#0x0
ETM Fifo Full Level Register
Bytes left in FIFO
https://github.com/cmsis-svd/cmsis-svd-data