Backup Fast RC (BFRC) Oscillator
The PIC32MZ oscillator system includes a Fail-Safe Clock Monitor (FSCM). The FSCM monitors the SYSCLK for continuous operation. If it detects that the SYSCLK has failed, it switches the SYSCLK over to the BFRC oscillator and triggers a non-maskable interrupt (NMI). The BFRC is an untuned 8 MHz oscillator that will drive the SYSCLK during FSCM event. When code at the NMI vector is executed, software can attempt to restart the main oscillator or shut down the system.
You cannot choose to use the BFRC for SYSCLK. Only the hardware will use this when the fail-safe clock monitor (FSCM) detects a problem.