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NRF52840dk enters bootloader mode without pushing reset button, when plugging J3 (nRF USB Connector) only

Andrea Aizza

Hi, 

setup: nrf52840 dk, no battery installed (power comes from USB connectors), switches are in default mode (SW9: VDD, SW6: default).  

Flashed open_bootloader (dfu/open_bootloader/pca10056_usb_debug/armgcc) via J2 (MCU USB) connection and nrfjprog (make flash_mbr && make flash). 

After this, I would like to only connect J3 (nRF USB). I can then flash with nrf-connect or nrfutil, but the issue is that every time I connect J3, bootloader mode is entered without pushing Reset button, so I cannot run the uploaded code (without reprogramming every time I unplug/plug J3). 

Note: if I plug J2 connector, instead of J3, then the app starts normally. 

I do not have a scope electrical signals... can anybody help or confirm this is normal?

Regards,

Andrea

  • +1

    Hi Andrea, 

    The open bootloader was made originally for the PCA10059 dongle. We designed with an option to enter bootloader mode via the pin reset (pressing Reset pin on the dongle) because there is only one button on the bootloader for application, we don't want to use that for the bootloader. 

    This applied for the firmware you flashed on the PCA10056. If there is an active signal on the reset pin, the board will enter bootloader mode. This is the case when you don't connect the board on J2, leaving pin P0.18 float and that trigger a reset when you plug USB onto J3. If you hold P0.18 to VDD, you should be able to enter application instead of bootloader. 

    Another option is to remove the code to enter bootloader when there is a pin reset. Please have a look into dfu_enter_check() in nrf_bootloader.c 

  • 0 in reply to Hung Bui

    Hi, 

    thanks! Just to check, uploading dfu/open_bootloader/pca10056_usb_debug/armgcc to PCA10056, without the above changes, results in entering bootloader when plugging only J3. Right? Just to be sure I am not running any hw issue. 

    Cheers,

    Andrea

  • 0 in reply to Andrea Aizza

    No, not your hardware issue. I saw the same thing on my board here :)  

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