How to reconnect to a board that errors when debug session starts?

[stephen_goodman]

I have been debugging code on the LPC 1769 LPCXpresso using MCUXpresso and a JLink debug probe. When I was last able to run a debug session the board programmed OK but the application did not run. By which I mean breakpoints I set were not hit and pausing the debug session did not halt within code. I stopped the debug session and tried to restart but I could no longer connect to the MCU.

There are a few error messages but I think the important ones are:

"AP[0]: Skipped. Invalid implementer code read from CPUIDVal[31:24] = 0x00"

"WARNING: RESET (pin 15) high, but should be low. Please check target hardware."

Thinking that it might be the on board CMSIS DAP debugger interfering with the JLink connection I used that debugger instead and got a similar error:

"connection failed - Ep(03). Invalid ID for processor"

I also tried using the GUI Flash Tool erase function:

"Cannot halt processor"
"connection failed - Ep(03). Invalid ID for processor"
"Expecting vector catch on SYSRESETREQ signal"

I have attached the console output for each attempt.

I have tried searching for help but cannot find anything helpful or relevant to my problem. Can someone give advice as to how this could have happened, what I should be looking for and how I could reconnect to the device again?

[stephen_goodman]

I managed to connect to the board and erase the MCU flash.  I did this by using the LPC11U35 CMSIS DAP to connect to the board rather than using the JLink.  When powering the board (plugging in the USB) I held down the reset button on the board.  I then used the GUI Flash Tool within the debug configuration for "C/C++ (NXP Semiconductors) MCU Application" to perform a mass erase.  I could then connect to it as normal.

The fault in the code was incorrect CPU clock configuration.