ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Application Level Programmers’ Model
A2.1 About the Application level programmers’ model
This chapter contains the programmers’ model information required for application development.
The information in this chapter is distinct from the system information required to service and support
application execution under an operating system. However, some knowledge of that system information is
needed to put the Application level programmers' model into context.
System level support requires access to all features and facilities of the architecture, a mode of operation
referred to as privileged operation. System code determines whether an application runs in a privileged or
unprivileged manner. When an operating system supports both privileged and unprivileged operation, an
application usually runs unprivileged. This:
permits the operating system to allocate system resources to it in a unique or shared manner
provides a degree of protection from other processes and tasks, and so helps protect the operating
system from malfunctioning applications.
This chapter indicates where some system level understanding is helpful, and where appropriate it:
gives an overview of the system level information
gives references to the system level descriptions in Chapter B1 The System Level Programmers’
Model and elsewhere.
The Security Extensions extend the architecture to provide hardware security features that support the
development of secure applications. For more information, see The Security Extensions on page B1-25.
A2-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B