The Reset Controller (RSTCTRL) is always enabled, but some of the Reset sources must be enabled (either by fuses or by software) before they can request a Reset.
After any Reset, the Reset source that caused the Reset is found in the Reset Flag register (RSTCTRL.RSTFR).
After a Power-on Reset, only the POR flag will be set.
The flags are kept until they are cleared by writing a '1' to them.
After Reset from any source, all registers that are loaded from fuses are reloaded.