nrf52840 locked in reset

[Neunz]

Hi 

We are using a nrf52840 on a custom board.

The board always worked fine. 

Flashing is done with :

    - SEGGER J-Link EFM32GG-STK3700 

    - nrfjprog version: 10.15.0 external

    - JLinkARM.dll version: 6.94a

    - Platform : Linux

We ported the sensor exemple from nrf5_SDK_for_Mesh_v5.0.0. to our custom board and it worked fine. 

Suddenly we were not able to erase/flash any code on it any more.

We discover that the reset pin is always low so it reboot in loop.

After soldering a 100 ohm pull up resistor we are again able to reset the board : 

nrfjprog --eraseall 

After this we can flash SoftDevice and Application.

Everything is working fine with the resistor. 

If we remove the pull-up resistor, as soon as we flash any application, including a simple Arduino blink example, the board is locked again in reset loop. 

We must right after the erase of the flash, do a : 

nrfjprog --recover -f nrf52

After that the application work only without CONFIG_GPIO_AS_PINRESET but then our reset button isn't working.

After some tests it happen that the bug only affect some boards and not other. 

Other boards work fine with CONFIG_GPIO_AS_PINRESET.

Is it possible that the state is not properly reset ? 

[Håkon Alseth]

Hi,

 

Are you using P0.18 as a generic GPIO in your application?

 

In the nRF52840, you can use the P0.18 as nRESET or as generic GPIO (via removing "CONFIG_GPIO_AS_PINRESET" in your preprocessor defines).

The default behavior is to use P0.18 as nRESET, so you have to first issue an erase-all (nrfjprog -e or nrfjprog --recover), then flash the device with your own firmware.

 

Kind regards,

Håkon

[Neunz]

Hi, 

We use it as reset pin. 

If "CONFIG_GPIO_AS_PINRESET"  is removed, the application work fine but not the reset button.

[Håkon Alseth]

Hi,

 

Neunz said:

If "CONFIG_GPIO_AS_PINRESET"  is removed, the application work fine but not the reset button.

Q1: Are you using P0.18 in your firmware?

Q2: Do you see this issue on other boards as well?

 

Kind regards,

Håkon

[Neunz]

Q1. We use sensor example from nRF5 SDK for Mesh v5.0.0, after the board is bricked the pin stay locked regardless of the firmware on board. 

Q2. We can not reproduce the issue on other board, even on our custom board the issue only happen on some but not every board. 

[Håkon Alseth]

Hi,

 

Neunz said:

Q2. We can not reproduce the issue on other board, even on our custom board the issue only happen on some but not every board. 

Since you do not see this issue on other boards, it is likely that this specific board has been ESD/EOS damaged on this specific pin.

That can happen if the pin is routed for longer instances, and exposed to the "environment" (for instance direct physical handling), without having ESD protection diode / series resistors to handle such scenarios.

 

I would recommend that you create a private ticket and ask for a hardware layout review, and specifically mention that you have had one board that has been problematic around the P0.18 pin (ESD/EOS).

 

Kind regards,

Håkon