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Programmer’s Model
ARM DDI 0192A
Copyright © ARM Limited 1997, 1998, 2000. All rights reserved.
2-7
2.5
Operating modes
The ARM720T supports seven modes of operation as listed in Table 2-1.
Changing modes
Mode changes can be made under software control, by external interrupts or during
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.
Table 2-1 ARM720T modes of operation
Mode
Type
Description
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 Abort or instruction Prefetch Abort
System
sys
A privileged User mode for the operating system
Undefined
und
Entered when an Undefined Instruction is executed
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