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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 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 ReferenceARM, Thumb, and ThumbEE state
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A processor that is executing ARM instructions is operating in ARM state. A processor that is executing Thumb instructions is operating in Thumb state.
A processor in one state cannot execute instructions from another instruction set. For example, a processor in ARM state cannot execute Thumb instructions, and a processor in Thumb state cannot execute ARM instructions. You must ensure that the processor never receives instructions of the wrong instruction set for the current state.
Most ARM processors always start executing code in ARM state. However, some processors can only execute Thumb code, or can be configured to start in Thumb state.
ThumbEE introduces a new instruction set state, ThumbEE state. In this state, instructions are executed as defined in the ThumbEE instruction set.
Each instruction set includes instructions to change processor state.
To change between ARM and Thumb states, you must switch the assembler mode to produce the correct opcodes using ARM or THUMB directives. To generate Thumb‑2EE code, use THUMBX. (Assembler code using CODE32 and CODE16 can still be assembled by the assembler, but you are recommended to use ARM and THUMB for new code.)
See Instruction set and syntax selection directives for details.
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