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JTAG Communication Failures

Sue Cozart
Guru 58650 points

It is possible to run code on a Tiva C Series device that causes the device to lose JTAG communication.  The two most common causes are:

  1. Changing the system clock speed to something that the target system does not support.
  2. Changing the function of the Port C[3:0] pins, which are muxed with the JTAG pins.

If you accidentally do either of these things, you can restore communication with your target device by running the Debug Port Unlock utility in LMFlash Programmer as shown below.  For Tiva devices, select the Fury, DustDevil and Blizzard option

On TM4C129x devices, the MAC address is erased by the Debug Port Unlock utility, so be sure to write down the number before running the utility.

Regards,

Sue

  • Prodigy 10 points
    Hi Sue,
    I have the TM$C1294XL board and I have written some wrong clock settings as follows,
    //SYSCTL_RSCLKCFG_R |= 0x13300003;
    //SYSCTL_PLLFREQ0_R |= 0X800060;
    //SYSCTL_PLLFREQ1_R |= 0X04;
    Also writtent some other settings in other registers accidently so the board is not getting programmed.

    After looking at this post I tried the above given method many times and followed the on screen instructions :
    1. assert (press) the reset button and keep it pressed.
    2. when said release the reset button
    3. again press the reset button and remove the power cable
    4. after powering release the button.

    I might be wrong in doing the procedure, so can you please guide me what else should I do , I am using the LM flash programmer build 1613.

    Thanks in advance
  • in reply to Rohit Deshpande
    TI__Guru**** 244380 points

    Hello Rohit,

    You have to Power up the board with Reset button pressed.

    Rohit Deshpande said:
    //SYSCTL_RSCLKCFG_R |= 0x13300003;
    //SYSCTL_PLLFREQ0_R |= 0X800060;
    //SYSCTL_PLLFREQ1_R |= 0X04;

    And let it be now recorded that DRM method for coding is not suggested but TivaWare API's are the correct coding method to follow.

    Regards

    Amit

  • in reply to Amit Ashara
    Guru 117855 points
    Hi Amit,

    BRAVO! Unguided posters DO require constant reminders, "NOT to use DRM or ASM" as this (substantially) increases the load upon you - thus decreases the numbers you can serve, here. That's simply unfair.

    Poster has dredged up 2+ year writing of Ms. Cozart - we should note that in addition to, "increasing wear/tear upon you, raising response time, posters (immensely) add to their odds of "breaking" their JTAG link via the use of the far more complex - and error-prone - DRM or ASM.
  • in reply to Amit Ashara
    Intellectual 510 points

    Hi Amit,

    when using this tool with selecting the Fury, DustDevil and Blizzard option.

    It will revert JTAG bits to work with communication Debugger with Erasing the Code in the flash  (Tiva will have no code on it here !)

    Is this right ?

    Regards,

  • in reply to ibrahem mostafa
    TI__Guru**** 244380 points
    Hello Ibrahem

    Blizzard is TM4C123x class of device and yes it will revert the device to factory condition.

    Regards
    Amit