ARM VERSION 1.2 - Manual (Page 336)

Directives Reference
7-54 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
7.7.3 CODE16 and CODE32
The CODE16 directive instructs the assembler to interpret subsequent instructions as
16-bit Thumb instructions. If necessary, it also inserts a byte of padding to align to the
next halfword boundary.
The CODE32 directive instructs the assembler to interpret subsequent instructions as
32-bit ARM instructions. If necessary, it also inserts up to three bytes of padding to
align to the next word boundary.
Syntax
CODE16
CODE32
Usage
In files that contain a mixture of ARM and Thumb code:
• Use CODE16 when changing from ARM state to Thumb state. CODE16 must precede
any Thumb code.
• Use CODE32 when changing from Thumb state to ARM state. CODE32 must precede
any ARM code.
CODE16 and CODE32 do not assemble to instructions that change the state. They only
instruct the assembler to assemble Thumb or ARM instructions as appropriate, and
insert padding if necessary.
Example
This example shows how CODE16 can be used to branch from ARM to Thumb
instructions.
AREA ChangeState, CODE, READONLY
CODE32
; This section starts in ARM state
LDR r0,=start+1 ; Load the address and set the
; least significant bit
BX r0 ; Branch and exchange instruction sets
; Not necessarily in same section
CODE16 ; Following instructions are Thumb
start MOV r1,#10 ; Thumb instructions