Operating Modes; Table 2-1 Register Mode Identifiers - ARM ARM7TDMI Technical Reference Manual

2.5

Operating modes

ARM DDI 0210C
The ARM7TDMI processor has seven modes of operation:
• User mode is the usual ARM program execution state, and is used for executing
most application programs.
• Fast Interrupt (FIQ) mode supports a data transfer or channel process.
• Interrupt (IRQ) mode is used for general-purpose interrupt handling.
• Supervisor mode is a protected mode for the operating system.
• Abort mode is entered after a data or instruction Prefetch Abort.
• System mode is a privileged user mode for the operating system.
Note
You can only enter System mode from another privileged mode by modifying the
mode bit of the Current Program Status Register (CPSR).
• Undefined mode is entered when an undefined instruction is executed.
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.
Each register has a mode identifier as listed in Table 2-1.
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Programmer's Model

Table 2-1 Register mode identifiers

Mode Mode identifier
User usr
Fast interrupt fiq
Interrupt irq
Supervisor svc
Abort abt
System sys
Undefined und
2-7