Cannot read DP STAT register, TDO/SWDIO pin held permanently low (K22)

[oj_willis]

I am using IAR Embedded Workbench with an I-Jet programmer to program a Kinetis K22 processor (MK22FN512VLL12) that is installed on our own custom board.

One board does not allow access to the debug port while others work fine. This is with the debugger probe set for a hardware reset. After the hardware reset TDO stays low and the DAP is not accessible. If I change the debugger probe setting to "No Reset", it then works fine. What would prevent access to the debug port after a reset and how do I fix it?

Here are some key excerpts from the log:

CoreSight error: Cannot read DP STAT register. No DAP access. Debugging is not possible.

 CMD_INTERPRETER: failed

C:\Program Files (x86)\IAR Systems\Embedded Workbench 8.2\arm\config\debugger\NXP\Kxx.dmac(91,18): Error: Operation error.

<Call to _ExecDeviceCoreConnect failed

Error while calling macro execUserCoreConnect

LowLevelReset(): Core 0: CpuStatus(status = <0x80: CPU_STATUS_MERR>) = 0

Debug Log(info): CPU status FAILED

>Calling _ExecDeviceCoreConnect

ISigCmdInterpreter::Execute('DAP.RDPw 0x08 0x010000f0')

JTAG test failed - the TDO/SWDIO pin held permanently low.CoreSight error : Firmware scan error (may indicate pending fault AP transaction that must be aborted).

[Alexis_A]

Dear OJ,

Did you have a development board or a J-Link debugger apart from the I-Jet? In the command line of the debugger you can use the command "unlock kinetis" that could help you to recover the MCU. Check more information about it in the following link.

Also, this could be due to a bad soldering, could you check that the reset circuit and the JTAG/SWD lines doesn't have any anomaly?

Let me know your findings.

Best Regards,

Alexis Andalon