ARM VERSION 1.2

Writing ARM and Thumb Assembly Language

Note

The label used with

ADR

ADRL

must be within the same code sect ion. The assembler

faults references to labels that are out of range in the same section. The linker faults

references to labels that are out of range in other code sections.

In Thumb state,

ADR

can generate word-aligned addresses only.

ADRL

is not available in Thumb code. Use it only in ARM code.

Example2-6 shows the type of code generated by the assembler when assembling

ADR

and

ADRL

pseudo-instructions. It is supplied as

adrlabel.s

in the

examples\asm

subdirectory of the ADS. Refer to Code examples on page2-2 for instructions on how

to assemble, link, and execute th e example.

The instructions listed in the comments are the ARM instructions generated by the

assembler.

Example2-6

AREA adrlabel, CODE,READONLY

ENTRY ; Mark first instruction to execute

Start

BL func ; Branch to subroutine

stop MOV r0, #0x18 ; angel_SWIreason_ReportException

LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit

SWI 0x123456 ; ARM semihosting SWI

LTORG ; Create a literal pool

func ADR r0, Start ; => SUB r0, PC, #offset to Start

ADR r1, DataArea ; => ADD r1, PC, #offset to DataArea

; ADR r2, DataArea+4300 ; This would fail because the offset

; cannot be expressed by operand2

; of an ADD

ADRL r2, DataArea+4300 ; => ADD r2, PC, #offset1

; ADD r2, r2, #offset2

MOV pc, lr ; Return

DataArea SPACE 8000 ; Starting at the current location,

; clears a 8000 byte area of memory

; to zero

END