TM4C1292NCPDT: I am not able to debug TM4c1292NCPDT through JTAG (Screenshot attached)

Hi,

  Is it possible that you wrote some code that caused the chip to lock up? Or this is a fresh chip that you have not downloaded any code yet?  If you can run test connection successfully then I think the JTAG scan chain is fine. 

  Normally, the chip can be locked in below three mostly seen cases.

  - The JTAG pins are repurposed for GPIO. Since JTAG pins are now just general GPIO pins, debugger can no longer access the target.

  - The device is put into deepsleep or hibernate mode without a mechanism to wake up. Once the device is in deep sleep or hibernate mode, there is no longer clocks running. Debugger cannot synchronize with the target if there is no clocks. 

  - Application specifically lock the JTAG access via BOOTCFG register. 

Parvez Akhtar Shaikh said:

how to unlock the microcontroller in this case ?

To unlock the device, see section 5.3.2 of this app note. https://www.ti.com/lit/an/spma075/spma075.pdf

I wrote an application which has neither of the reason you have mentioned

1. I have not used JTAG Pins in my application

2. I have not used and hibernation or deepsleep feature.

3. I have also not configured BOOTCFG in my application.

I was able to download my application to the target first time after that I am not even able to connect it.

I am also not able to unlock the device following the procedure as mentioned in document. I want to understand what else could have gone wrong ? I don't want to repeat the same mistake.

Parvez Akhtar Shaikh said:

I was able to download my application to the target first time after that I am not even able to connect it.

Can you show your application? As you can download the application the first time, it seems to suggest that something in your code caused the device to lock up.  

It is a big application. I am using FreeRTOS, LWIP, external PHY etc.

This application is already running in TM4c1294NCPDT. The only change I have done is changed the Ethernet driver from internal PHY to External PHY. I don't think this should cause any issue.

As I mentioned above I have not used JTAG pins, deepsleep or BOOTCFG in my application.

The below link has some tips on JTAG troubleshooting. The error you get is related to Error - 1170. According to the description, it is most likely caused by a hardware failure on the board. 

https://software-dl.ti.com/ccs/esd/documents/ccs_debugging_jtag_connectivity_issues.html#cannot-access-the-dap

Cannot access the DAP

This error is caused by the inability of the JTAG debugger to access the DAP or one of its ARM subcores. This is usually caused by either a hardware failure on the board or invalid code on the subcore that causes it to reset itself continuously.

- Can you retry the unlock procedure? You mentioned that it didn't unlock for you. Please try again and show the output of the unlock.

- Do you have another board that you can load the same firmware and use the same PC and the same debug probe to access the target?

- Do you have another debug probe? Can you repeat the same problem using a different debug probe?

- To isolate if it is a MCU or a board level problem, can you do a ABA swap test. Swap a new MCU to your existing board. Can you repeat the same problem after a couple of firmware downloads? With the bad MCU swapped to a good known board, does it continue to fail - unable to connect to the target.