Cortex-A8 Technical Reference Manual: 2.12. Operating modes

2.12. Operating modes

There are eight modes of operation:

User mode is the usual ARM program execution state, and is used for executing most application programs
Fast interrupt (FIQ) mode is used for handling fast interrupts
Interrupt (IRQ) mode is used for general-purpose interrupt handling
Supervisor mode is a protected mode for the OS
Abort mode is entered after a data abort or prefetch abort
System mode is a privileged user mode for the OS
Undefined mode is entered when an Undefined Instruction exception occurs
Monitor mode is a Secure mode for the Security Extensions Secure Monitor code.

Modes other than User mode are collectively known as privileged modes. Privileged modes are used to service interrupts or exceptions, or to access protected resources. Table 2.8 shows the mode structure for the processor.

Table 2.8. Mode structure

Modes	Mode type	Security state of core
		NS bit = 1	NS bit = 0
User	User	Nonsecure	Secure
FIQ	Privileged	Nonsecure	Secure
IRQ	Privileged	Nonsecure	Secure
Supervisor	Privileged	Nonsecure	Secure
Abort	Privileged	Nonsecure	Secure
Undefined	Privileged	Nonsecure	Secure
System	Privileged	Nonsecure	Secure
Monitor	Privileged	Secure	Secure

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