3.3.3. Operating modes

ARM720T supports seven modes of operation:

Table 3.1. ARM720T modes of operation

ModeTypeDescription
User(usr)The normal ARM program execution state
FIQ(fiq)Designed to support a data transfer or channel process
IRQ(irq)Used for general-purpose interrupt handling
Supervisor(svc)Protected mode for the operating system
Abort mode (abt)Entered after a data or instruction prefetch abort
System (sys)A privileged user mode for the operating system
Undefined(und)Entered when an undefined instruction is executed

Changing modes

Mode changes may be made under software control, or may be brought about by external interrupts or exception processing. Most application programs execute in User mode. The non-User modes—known as privileged modes—are entered in order to service interrupts or exceptions, or to access protected resources.

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