ARM Technical Support Knowledge Articles

Why is my target not responding to debug commands after connection with RVD?

Applies to: RealView Development Suite (RVDS)

Answer

RealView Debugger (RVD) will attempt to stop the target as part of the default connection sequence. If the hardware does not respond to the stop request as expected, the debugger will not have any control over the target and subsequent debug commands will fail.

You should see an error message in RVD's Command Pane indicating that the stop request has failed. Depending on the version of RVD the message could be one of the following:

This problem is typically encountered if the target system bus is locked up. This can be caused by a memory access (after reset or during program execution) to invalid areas of the memory map which do not return a valid response from a slave. With the system bus locked up the processor will not enter debug state and can therefore not be stopped.

The solution requires the follow special connection sequence:

  1. Connect to the target using RVD's 'No Reset No Stop' connection mode. The target connection will be made without attempting to stop the processor (enter debug state).
  2. With RVD connected, place a hardware breakpoint at address 0x0 (with the core still running, i.e., locked up)
  3. Now issue a system reset ('Reset Target Processor' from within RVD)

The processor should now stop on address 0x0 and you should have full control of your target.

Please note that the reset request in the debugger will assert the nSRST line on the JTAG port. The nSRST line should only reset the processor without resetting the JTAG TAP controller (nTRST). If the JTAG TAP is reset (for non-Coresight systems) the breakpoint we have placed will be lost and the reset will not be trapped at address 0x0. The recovery procedure will fail if the target has the nTRST and nSRST pins connected together.

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