[ABANDONED] Losing JTAG connection

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  • [ABANDONED] Losing JTAG connection

    Hello,

    I try to tamper with a device that uses an ARM926EJ-S core. I connected my J-Link EDU and on the software side I use JLinkGDBServer with IDA. In the earlier stages of device boot I can halt the execution, read memory, execute steps and all. But at some stage of the boot process I get the following log message:

    02-00000000-00-00044481-000F: ***** Error:
    02-00000000-00-00044481-0071: T58FF7700 044:482.210 Bad JTAG communication: Write to IR: Expected 0x1, got 0x0 (TAP Command : 12) @ Off 0x14.
    02-00000000-00-00044481-002D: T58FF7700 044:482.234 - 0.285ms returns FALSE
    03-00000000-00-00044481-0062: ERROR: Bad JTAG communication: Write to IR: Expected 0x1, got 0x0 (TAP Command : 12) @ Off 0x14.

    Sometimes it's instead a


    ERROR: Bad JTAG communication: Write to IR: Expected 0x1, got 0x0 (TAP Command : 2) @ Off 0x5.

    From then on the target cannot be halted anymore:

    03-00000000-00-00047761-0025: Debugger requested to halt target...
    02-00000000-00-00047761-0022: T58FF7700 047:761.618 JLINK_Halt()
    02-00000000-00-00047761-002C: T58FF7700 047:761.646 - 0.029ms returns 0x01
    02-00000000-00-00047761-0026: T58FF7700 047:761.670 JLINK_IsHalted()
    02-00000000-00-00047761-002D: T58FF7700 047:761.692 - 0.024ms returns FALSE
    01-0000000B-00-00047761-0017: $T05thread:0000DEAD;#74
    00-0000000B-00-00047761-0010: $qfThreadInfo#bb
    01-0000000B-00-00047761-000D: $m0000dead#bb
    00-0000000B-00-00047761-0010: $qsThreadInfo#c8
    01-0000000B-00-00047761-0005: $l#6c
    00-0000000B-00-00047761-0005: $g#67

    and all registers are read as DEADBEEF.

    Could anyone please tell me what events can cause this to happen on this platform, so I can search and try to circumvent these?
  • Hi,
    Thank you for your inquiry.

    It looks like your application prevents JTAG communication in some way (e.g. by powering off the DAP).

    Do you use any low power modes? If so:
    wiki.segger.com/UM08001_J-Link…Guide#Low_Power_Debugging

    Additionally, you could step through the code and see at which point/instruction the debug session stops working.
    I would suspect that it is always the same code section.

    Best regards,
    Fabian
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