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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 ReferenceLoading constants into registers
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| Home > Writing ARM Assembly Language > Loading constants into registers | |||
You cannot load an arbitrary 32‑bit immediate constant into a register in a single instruction without performing a data load from memory. This is because ARM and Thumb-2 instructions are only 32 bits long. The range of constants that you can generate using 16-bit Thumb instructions is much smaller.
You can also include many commonly used constants directly as operands within data processing instructions, without a separate load operation.
You can load any 32‑bit value into a register with a data load, but there are more direct and efficient ways to load many commonly used constants.
In ARMv6T2 and above, you can also load any 32‑bit value into a register with two instructions, a MOV followed by a MOVT. You can use a pseudo‑instruction, MOV32, to construct the instruction sequence for you.
The following sections describe:
how to use the
MOVandMVNinstructions to load a range of immediate values.how to use the
MOV32pseudo‑instruction to load any 32‑bit constant.See Loading with MOV32.
how to use the
LDRpseudo‑instruction to load any 32‑bit constant.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0379A |
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