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Detecting JTAG connection from CPU

yuri poliak
Note: This was originally posted on 11th June 2013 at http://forums.arm.com

Hi all.

I am interested to know if during the initialization process while connecting Jtag debugger to ARM device such as cortex a9, there any way to indicate from the Kernel that this interface is in use?
i would like to know if the initialization process before halting the system is using any CPU register?

thank you
  • Note: This was originally posted on 13th June 2013 at http://forums.arm.com

    Thank you for the information.
    Can you please direct me to some official paper or document that prove that "[color=#222222][font=Arial, Helvetica, sans-serif][size=2]there is no way to determine if a JTAG debugger is connected"?[/size][/font][/color]
    [color=#222222][font=Arial, Helvetica, sans-serif][size=2]
    [/size][/font][/color]
    [color=#222222][font=Arial, Helvetica, sans-serif][size=2]Thank you[/size][/font][/color]
  • Note: This was originally posted on 13th June 2013 at http://forums.arm.com

    [size=2]I know that when i connect JTAG debugger, there are several initialization process between the debugger and the mobile phone. One of the things that happen during this initialization is  halting the CPU. [/size]
    [size=2]I want to build kernel module that will indicate that a JTAG debugger is now trying to communicate with the CPU, before that the system has been halted. In other words does the kernel can read the registers that are used during the initialization process or during the halting process? does the halting instruction is atomic(happens immediately ? does the Kernel can indicate that halting is going to happen?[/size]
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    [/size]
    [size=2]
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    [size=2]Thank you! [/size]
  • Note: This was originally posted on 14th June 2013 at http://forums.arm.com

    Hello, all!
    I try to be connected through JTAG to the ARM1136JF-S AT840 processor. The special place for JTAG on the printed-circuit board isn't present. I looked at all documentation at this processor, but I didn't find appointment and position of legs of the processor. Help, please! Thanks!
  • Note: This was originally posted on 12th June 2013 at http://forums.arm.com

    Hi, there is no way to determine if a JTAG debugger is connected.  There are ways to prevent a JTAG debugger being able to debug the core (see NIDEN and SNIDEN signals).  Generally, JTAG debuggers do not (and mostly cannot) access ARM core registers while a core is running.  If you are interested in capturing the history of a running system then you should investigate trace functionality provided by debug hardware units such as ARM's DSTREAM.

    Regards,
    Mike.
  • Arm Employee Badge
    Note: This was originally posted on 13th June 2013 at http://forums.arm.com

    Depending on why you'd want to know whether a debugger was attached, it might be possible to infer the presence.  For example, the debug logic is configured for Monitor mode debug by default.  If you saw the configuration had changed to Halt mode (and your code hadn't done it) you could infer that a debugger had attached.