2.2.4. Processor mode

ARM processors support different processor modes, depending on the architecture version (see Table 2.1).

Table 2.1. ARM processor modes

Processor modeArchitecturesMode number
FIQ - Fast Interrupt RequestAll0b10001
IRQ - Interrupt RequestAll0b10010
SystemARMv4 and above0b11111
MonitorSecurity Extensions only0b10110

All modes except User mode are referred to as privileged modes. They have full access to system resources and can change mode freely.

Applications that require task protection usually execute in User mode. Some embedded applications might run entirely in Supervisor or System modes.

Modes other than User mode are entered to service exceptions, or to access privileged resources (see the Handling Processor Exceptions chapter in RealView Compilation Tools v2.2 Developer Guide).

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