ARM VERSION 1.2

Writing ARM and Thumb Assembly Language

In an ARM assembly language source file, the start of a section is marked by the

AREA

directive. This directive names th e section and sets its attributes . The attributes are

placed after the name, separated by commas. Refer to AREA on page7-52 for a detailed

description of the syntax of the

AREA

directive.

You can choose any name for your sections. However, names starting with any

nonalphabetic character must be enclosed in bars, or an

AREA name missing

error is

generated. For example:

|1_DataArea|

Example2-1 on page 2-15 defines a single section called

ARMex

that contains code and

is marked as being

READONLY

The ENTRY directive

The

ENTRY

directive marks the first instruction to be executed. In applications containing

C code, an entry point is also contained within the C library initialization code.

Initialization code and exception handlers also contain entry points.

Application execution

The application code in Example2-1 on page 2-15 begins executing at the label

start

where it loads the decimal values 10 and 3 into registers r0 and r1. These registers are

added together and the resul t placed in r0.

Application termination

After executing the main code, the application terminates by returning control to the

debugger. This is done using the ARM semihosting SWI (

0x123456 by default

), with

the following parameters:

•r0 equal to

angel_SWIreason_ReportException

(

0x18

)

•r1 equal to

ADP_Stopped_ApplicationExit

(

0x20026

Refer to the Semihosting SWIs chapter in ADS Debug Target Guide for additional

information.

The END directive

This directive instructs the assembler to stop processing this source file. Every assembly

language source module must finish with an

END

directive on a line by itself.