ARM DS-5 Using the Debug Hardware Configuration Utilities

Debugging with your debug hardware unit8.7 Processor exceptionsDepending on implementation options, most ARM processors provide dedicated hardware toenter debug state when a predetermined event occurs.Most recent ARM processors provide hardware for trapping exceptions. When enabled, theeffect is similar to placing a breakpoint on the selected vector table entry. This is called vectorcatch. However:• Some ARM processors, such as ARM7, do not provide vector catch hardware. For theseprocessors, debug hardware simulates vector catch using instruction breakpoints.• For Cortex-M3, this is equivalent to putting a breakpoint at the target of the vector.Cortex-M3 has a restricted set of vector catches available.• If the exception vectors are in ROM, debug hardware must use hardware breakpoints tosimulate vector catch. This reduces the number of resources available for other purposes,if the processor does not have vector catch support.When the debug hardware simulates vector catch on earlier ARM processors that do not havevector catch support, it uses a software breakpoint when the vector table is located in RAM.You must take care when debugging through a system reset. Some hardware targets alter thememory map after reset, so the location of in physical memory containing software breakpointmight not be in the correct reset position. The following warning is output to the your debuggerconsole if debug hardware simulates reset vector catch using an instruction breakpoint:Warning: A software breakpoint is being used to simulate reset vector catch.This may fail to be hit if the memory is remapped when a reset occurs.The exact behavior of the ARM vector catch hardware depends on the processor. ARM9processors enter debug state only when the specified exception occurs. Other processors, suchas ARM11 or older processors that use a breakpoint, enter debug state whenever the instructionat the exception vector is executed, regardless of whether the exception occurs or not.8.7.1 See alsoConcepts• Hardware breakpoints on page 8-8• Software instruction breakpoints on page 8-9• Breakpoints and the program counter on page 8-11• Interaction between breakpoint handling in the debug hardware and your debugger onpage 8-12• Problems setting breakpoints on page 8-14.ARM DUI 0498F Copyright © 2010-2012 ARM. All rights reserved. 8-10ID021112Non-Confidential