ARM DS-5 Using the Debug Hardware Configuration Utilities

Debugging with your debug hardware unit8.14 Debugging from resetYou can debug systems running in ROM. A typical embedded system has the applicationprogrammed in non-volatile memory, such as ROM or Flash. When target hardware is poweredup, the application starts running. When connecting the debugger to a target already running theapplication, the application stops at an arbitrary point in the code. The default behavior of thedebugger is to stop the target on connection. Loading the image symbols gives you source codeview of the current location.This means that you can examine the state of the system and restart execution from the currentplace. In some cases, this is sufficient. However, in many cases it is preferable to restartexecution of the application as if from power-on. There are three ways to do this:• debugging with a simulated a reset• debugging with a reset register• debugging with a target reset.When you debug code that is running from ROM, you must ensure that at least one breakpointunit remains available so that you can set breakpoints on code in ROM, because you cannot usesoftware breakpoints for this purpose. On a processor without vector catch hardware, you mustdisable semihosting and vector catching as soon as possible after starting up the debugger. Thiscan reduce the chances of the debugger taking these units for its own use.On ARM processors that use a breakpoint resource to implement software breakpoints, such asthe ARM7TDMI, you must remove all software breakpoints if you are out of breakpointresources. This enables you to place a single hardware breakpoint in ROM.Another factor in debugging a system in ROM is that the ROM image does not contain anydebug information. When debugging, symbol or source code information is available by loadingthe relevant information into the debugger from the ELF image on the host.8.14.1 See alsoTasks• Post-mortem debugging on page 8-2.Concepts• Debugging with a simulated reset on page 8-19• Debugging with a reset register on page 8-20• Debugging with a target reset on page 8-21• Debugging systems with ROM at the exception vector on page 8-22.ARM DUI 0498F Copyright © 2010-2012 ARM. All rights reserved. 8-18ID021112Non-Confidential