The mechanisms by which the physical processor can enter monitor mode from the
Normal world are tightly controlled, and are all viewed as exceptions to the monitor
mode software. The entry to monitor can be triggered by software executing a dedicated
instruction, the Secure Monitor Call (SMC) instruction, or by a subset of the hardware
exception mechanisms. The IRQ, FIQ, external Data Abort, and external Prefetch Abort
exceptions can all be configured to cause the processor to switch into monitor mode.