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RealView Assembler User's Guide
Preface Introduction 
Writing ARM Assembly Language 
Introduction Overview of the ARM architecture Architecture versions ARM, Thumb, Thumb-2, and Thumb-2EE instruction set ARM, Thumb, and ThumbEE state Processor mode Registers Instruction set overview Instruction capabilities Structure of assembly language modules Layout of assembly language source files An example ARM assembly language module Calling subroutines Conditional execution The ALU status flags Conditional execution Using conditional execution Example of the use of conditional execution The Q flag Loading constants into registers Direct loading with MOV and MVN Loading with MOV32 Loading with LDR Rd, =const Loading addresses into registers Direct loading with ADR and ADRL Loading addresses with LDR Rd, =label Load and store multiple register instructions Load and store multiple instructions available in Implementing stacks with LDM and STM Block copy with LDM and STM Using macros Test-and-branch macro example Unsigned integer division macro example Using frame directives Assembly language changes Assembler Reference ARM and Thumb Instructions Directives ReferenceProcessor mode
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ARM processors support different processor modes, depending on the architecture version (see Table 2.1).
Note
ARMv6-M and ARMv7-M do not support the same modes as other ARM processors. This section does not apply to ARMv6-M and ARMv7-M.
Table 2.1. ARM processor modes
| Processor mode | Architectures | Mode number |
|---|---|---|
| User | All | 0b10000 |
| FIQ - Fast Interrupt Request | All | 0b10001 |
| IRQ - Interrupt Request | All | 0b10010 |
| Supervisor | All | 0b10011 |
| Abort | All | 0b10111 |
| Undefined | All | 0b11011 |
| System | ARMv4 and above | 0b11111 |
| Monitor | Security Extensions only | 0b10110 |
All modes except User mode are referred to as privileged modes. They have full access to system resources and can change mode freely. User mode is an unprivileged mode.
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.
On architectures that implement the Security Extensions, code can run in either a secure state or in a non-secure state. See the ARM Architecture Reference Manual for details.
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