ARM VERSION 1.2 - Manual (Page 235)

Thumb Instruction Reference
ARM DUI 0068B Copyright © 2000, 2001 ARM Limited. All rights reserved. 5-41
5.6.2 LDR Thumb pseudo-instruction
The LDR pseudo-instruction loads a low register with either:
• a 32-bit constant value
• an address.
Note
This section describes the LDR pseudo-instruction only. See Thumb memory access
instructions on page 5-4 for information on the LDR instruction.
Syntax
LDR register, =[expr | label-exp]
where:
register is the register to be loaded. LDR can access the low registers (r0-r7) only.
expr evaluates to a numeric constant:
• if the value of expr is within range of a MOV instruction, the
assembler generates the instruction
• if the value of expr is not within range of a MOV instruction, the
assembler places the constant in a literal pool and generates a
program-relative
LDR instruction that reads the constant from the
literal pool.
label-exp is a program-relative or external expression. The assembler places the
value of
label-exp in a literal pool and generates a program-relative LDR
instruction that loads the value from the literal pool.
If label-exp is an external expression, or is not contained in the current
section, the assembler places a linker relocation directive in the object
file. The linker ensures that the correct address is generated at link time.
The offset from the pc to the value in the literal pool must be positive and less than 1KB.
You are responsible for ensuring that there is a literal pool within range. See LTORG on
page 7-14 for more information.
Usage
The LDR pseudo-instruction is used for two main purposes:
• To generate literal constants when an immediate value cannot be moved into a
register because it is out of range of the
MOV instruction.