ARM ARM DUI 0137A Configuring AXD to enable tracing with RMHost, Performance of RMHost with TDT

Debugging with RMHost

3.3.1Configuring AXD to enable tracing with RMHost

The process of connecting to a target system using both RMHost and TDT is similar to connecting to a target system using only RMHost. The only difference is that you must enable tracing when you configure your JTAG controller to be used with RealMonitor.dll, as described in step 6 of Procedure for connecting to RMHost using AXD on page 22. For details on enabling tracing, see the appendix on setting up the trace software in the Trace Debug Tools User Guide.

3.3.2Performance of RMHost with TDT

When using TDT with Multi-ICE only, and not RMHost, TDT cannot read the target memory without halting the processor. However, it must be able to view the instructions that were executed by the processor to decode the trace data. It therefore implements an image cache in the host, and fetches the instructions from this cache, rather than from the target.

Note

If your image is already loaded onto the target, you can select Load Debug Symbols from the File menu to place the image into the image cache (even while your application is currently running).

Caution

If you are using self-modifying code, you must disable the image cache in the debugger because when the image cache is in use, the debugger cannot detect any modifications the code makes to itself. To disable the image cache in AXD:

1.Select Debugger Internals from the System Views menu.

2.Change the value of the variable image_cache_enable from 0x01 to 0x00.

With RMHost, it is possible to read memory without halting the target, and TDT can decode the trace data by reading memory on the target. Therefore, a trace stream can be displayed without having to use the image cache.

However, because the link between the host and the target is limited by the JTAG connection, and the performance of the debug communications channel when using RMHost, decoding trace in this way is slow compared to using the image cache.

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