NRF52840 repeated reboot without debugger

[gauthamkarnik]

Hi, we are trying to work with nRF52840. We have a problem that our hardware goes into continuous reboot mode when we disconnect the JLINK debugger. The disconnect can be a hard disconnect or a soft disconnect when the debugger is "clicked" to disconnect. Seems like the crystals are not stable enough. This is just a guess.

Environment:

Debugger: IAR Workbench with JLINK debugger

Crystals: ABM11W-32.0000MHZ-8-D1X-T3, ECS-.327-12.5-34B

Load capacitors: 04025A100JAT2A

The UART which is configured at the start up seems to lose its setting. By default the idle state of an UART line is high. However, when the debugger is disconnected, I can see pulses on this UART line which seems to me that the software is trying to configure the UART but reboots eventually after that.

Please let me know what the bug is.

[Sigurd]

Hi,

A reset indicates that you are running into the error handler, where the default behavior is to do a reset.

Have you enabled UART logging, do you gey any output from the UART?

Could you set the DEBUG preprocessor flag: 

Is the UART RX pin connected to anything?

[gauthamkarnik]

We do not have the debug UART enabled. I will look at the Debug Processor flag.

Even if the debug UART is enabled I do not suppose we could see anything when the processor resets.

We have also tested this on the Evaluation board (nRF52840 Eval board) and set up the board to

* run with external battery

* run in "nRF Only" mode

The behavior is similar to what we are seeing with our custom HW.

[Sigurd]

gauthamkarnik said:

Even if the debug UART is enabled I do not suppose we could see anything when the processor resets.

 That is the reason why we add the DEBUG Processor flag, it will prevent the reset, and should instead print the error-code.

gauthamkarnik said:

* run in "nRF Only" mode

 Do you see any difference if you set it to "DEFAULT" instead?

[gauthamkarnik]

I agree with you on the DEBUG processor flag. I was just referring to the debug uart and not the flag.

Regarding the DEFAULT Mode, every thing works fine. As long as we have the JTAG communications things work fine.

Does this have anything to do with Watchdog?