Entering Serial DFU mode from the application layer in nrf52840 dk board

[Gireesha]

Hi All,

I am trying  to implement UART SERIAL Bootloader for my device and I just need to perform DFU using uart serial without pressing BUTTON 1 and RESET buttons in nrf52840 dk board

My query is Without pressing BUTTON_1 and Power RESET how to enter to DFU mode from the application layer.

~Thanks

[Amanda Hsieh]

Hi, 

In the DFU mode, the bootloader activates the DFU transports and the device is ready to receive new firmware. The bootloader enters the DFU mode on the following conditions:

• No valid application is present.
• SoftDevice is activated and a valid application is present. In that case, the bootloader expects that an application update can be requested by the host.
• Entering DFU mode is triggered by one of the optional sources:
  • Button (NRF_BL_DFU_ENTER_METHOD_BUTTON),
  • Pin reset (NRF_BL_DFU_ENTER_METHOD_PINRESET),
  • Special value in GPREGRET register (NRF_BL_DFU_ENTER_METHOD_GPREGRET),
  • Request from the application written to the settings page (NRF_BL_DFU_ENTER_METHOD_BUTTONLESS).

See DFU mode doc.

Regards,
Amanda

[Gireesha]

Hello,

I am able to successfully put the device into bootloader mode by pressing the button 1 and reset button and we are able to perform DFU.

But, now in our custom device (nrf52840) doesn't have any button (reset / button). How do we implement this DFU method for our custom board. 

means how to enter DFU mode from application witout using any buttons.

~Thanks

[Amanda Hsieh]

Hi, 

You can enable NRF_BL_DFU_ENTER_METHOD_GPREGRET in the sdk_config.h, and write the special value in the retention register GPREGRET register a flag (BOOTLOADER_DFU_START = 0xB1)  in the application and then do a soft reset (NVIC_SystemReset) to switch. 

Since the retention register keeps its value after the reset, the bootloader will check this value when it boots up after the reset and then can enter DFU mode instead of starting the normal application. This is the same as when we hold the Bootloader button and trigger a reset.

Regards,
Amanda