cannot enter bootloader mode on nrf52840 dongle anymore

[Ivo H]

Dear all,

I could happily flash my firmware to my nrf52840 upon pressing reset button. When pressing the reset button the diode on the board started to beat red and via command:

nrfutil dfu usb-serial -pkg blinky.zip -p /dev/ttyACM0

I could easily write a new firmware.

Today I found a pair of scissors accidentally touching my board on GPIO pins, I immediately removed the scissors knowing it could potentially damage the board via short circuit. I removed the board from USB port and plugged it back. The application written on the flash is working correctly, it is a bluetooth flash button service, which can be controlled via Android app NRF Blinky. The diode can be controller correctly, it flashes upon command and also the button sends notification to my Android phone. So far it seems allright.

BUT, after I long press the reset button to enter bootloader mode, the diode does not glow read like heartbeat anymore, it tries to glow red and starts flashing red randomly like a current it flowing throught the diode randomly. Therefore I cannot write any new firmware to my board.

Moreover, I used to recover my dongle when accidentally locking my nrf52840 via OpenOCD, but right now, it cannot even connect to the device yielding:

Error: Error connecting DP : cannot read IDR

Does anyone know how to resolve this issue?

I suspect I damaged partially my board shortcutting it but I still wonder wheter there is a sort of a utility I can verify what is wrong exactly with my board. Just the bootloader might be corrupted but it is very suspicious that OpenOCD cannot communicate with the MCU via OpenOCD anymore.

Thank you very much

[Ivo H]

Actually,do you happen yo know if there is any way how to check the pin reset works as expected?Lets say,which voltage level on which part should I meaure and reading should I get phen pressing the switch button.

Or is there any other way I can switch yo bootloader mode apart from that reset button switch?This way I can verify that the bootloader works fine and the problem is somewhere on the physical board.I guess the reset button brings some voltage on the reset pin.

[Ivo H]

Oh,now I see I can activate the DFU mode from NRF Connect for desktop without pressing the reset button.

[Hung Bui]

Hi, 
Could you confirm that it works with the nRF Connect for desktop to put the chip to DFU mode ? 
Actually the way nRF Connect for Desktop work is to send a command to the USB interface so that the application firmware trigger a pin reset using P0.19 . 
So it's almost the same as pressing the reset button but via software. 
I think there must be something wrong with the hardware on the board maybe some kind of short  on one of the pins ? 

[Ivo H]

I would like to,but NRF Connect does not detect any of my two boards.Actually,the not broken ones shows something but I am facing an error message that the software cannot read firmware version.

I do not have any ST Link or Segger probe?Is it necessary to have such a probe to enter the USB dongle DFU mode via nrf Connect (without physically pressing the reset button) or just plugging in the dongle to USB is the only necassary condition to be able to enter DFU mode via nrf connect?

I checked the voltage on reset button and pressing the button exposes the internal pi (you say p0.19) to GND voltage,assuming you say the pin could be shortcutted to groung,the chip will be resetting all the time not being even able to run my code,right?

If the shortcut voltage would be different from GND voltage,does the DFU mode check for a certain voltage level in DFU mode or isn't the the RED heartbeating diode feeded from the pin 0.19 in DFU mode?I will compare voltages on the other side of the button in DFU mode for both of my dongle,it the voltage on the broken on differs,there is probably something wrong.

[Hung Bui]

Hi Ivo, 

So both of the board are not detectable ?

On the "not broken" one , can you put it to the DFU mode by pressing the reset button (the one on the side not the bigger oen) would it switch to DFU mode (LED grows red) ? 

You don't need an external programmer to access the chip when it's in DFU mode. It should work with nRF Connect. 

But if you have a programmer or a NRF5 DK you can use the DK to program the dongle directly. You would need to solder a 10 pin header on P1 port and use the 10pin cable like this one to program it from the Debug out port of the NRF5 DK. 

https://www.adafruit.com/product/1675

If you can program the dongle directly you don't need to use the DFU mode and can use the dongle the same way as the DK.