ARM DS-5 Using the Debug Hardware Configuration Utilities

Debugging with your debug hardware unit8.1 Post-mortem debuggingPost-mortem debugging enables you to examine the state of a system that has previously beenrunning but is currently not connected to debug hardware.8.1.1 PrerequisitesBefore you can examine a running target with debug hardware, you must configure the debughardware unit for that target. If you have a target that is operating without a debug hardware unitconnected, and you want to examine it to find out why it is behaving in a particular way, youmust power-up the debug hardware unit and configure the connection without disturbing thestate of the target. This requires that the debug hardware unit is powered before it is connectedto the target.The debug hardware unit includes power conditioning and switching circuitry that enables youto plug and unplug the JTAG cable without affecting the target.NoteThe voltage reference used by the debug hardware unit JTAG circuit is generated from theVTref signal present on the JTAG connector. If this signal is not connected at the target, youmust modify the target or the JTAG cable to supply a suitable reference. Connecting VTref toVsupply is usually sufficient.8.1.2 ProcedureTo connect to a running target:1. Ensure that the JTAG input lines TDI, TMS, nSRST, and nTRST have pull-up resistors(normal practice), and TCK has a pull-down resistor, so that when the adaptor isdisconnected from the target these lines are in their quiescent state.2. Plug the power jack into the debug hardware unit and wait for it to boot.3. Configure the debug hardware connection. You must do one of the following:• load a configuration that you have previously saved• manually configure the connection• autoconfigure using a separate test system.NoteDo not use autoconfigure on the target to be debugged, because doing so might reset theprocessor.4. If the target processor, such as an ARM7TDMI, does not have any system registers, youmust explicitly configure the endianness.NoteDo not automatically detect the endianness of target processors that do not have a systemregister. Doing so might disturb the state of the processor.5. Plug the JTAG cable into the target.CautionTo prevent unwanted resets during connection of the debug hardware, it is essential thateither:• the target and debug hardware are properly earthedARM DUI 0498F Copyright © 2010-2012 ARM. All rights reserved. 8-2ID021112Non-Confidential