Cortex-A8 R2P2.pdf - ARM Information Center

Debug12.2 About the debug unitThe processor debug unit assists in debugging software running on the processor. Youcan use the processor debug unit, in combination with a software debugger program, todebug:• application software• operating systems• hardware systems based on an ARM processor.The debug unit enables you to:• stop program execution• examine and alter processor and coprocessor state• examine and alter memory and input/output peripheral state• restart the processor core.You can debug software running on the processor in the following ways:• Halting debug-mode debugging• Monitor debug-mode debugging• trace debugging, see Chapter 14 Embedded Trace Macrocell.The processor external debug interface is compliant with the AMBA 3 APB ProtocolSpecification.12.2.1 Halting debug-mode debuggingWhen the processor debug unit is in Halting debug-mode, the processor halts when adebug event, such as a breakpoint, occurs. When the processor is halted, an externaldebugger can examine and modify the processor state using the APB interface. Thisdebug mode is invasive to program execution.12.2.2 Monitor debug-mode debuggingWhen the processor debug unit is in Monitor debug-mode and a debug event occurs, theprocessor takes a debug exception instead of halting. A special piece of software, amonitor target, can then take control to examine or alter the processor state. Monitordebug-mode is essential in real-time systems where the processor cannot be halted tocollect debug information. Examples of these systems are engine controllers and servomechanisms in hard drive controllers that cannot stop the code without physicallydamaging the components.12-4 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E