nRF52840 DFU Reset Reason Detection Issue

[luqman]

Problem:

• Reset reason logic works correctly when programming via SWD
• After DFU programming, reset reasons are detected incorrectly
• Even after unplugging/reconnecting the battery post-DFU, the logic fails
• DFU resets are being misclassified as "button press" instead of "system reset"

void analyze_wakeup_reason(void) {
  int32_t reset_reason = NRF_POWER->RESETREAS;
  NRF_POWER->RESETREAS = NRF_POWER->RESETREAS;
  
  if (reset_reason == 0x00040000 || reset_reason == 0x00000000) {
    // Full reset (battery change)
    wakeUpCheck = true;
    batresetResion = true;
  } else {
    // Button press wakeup - BUT DFU resets incorrectly end up here!
  }
}

What I've observed:

• SWD programming: Reset reasons detected correctly
• DFU programming: All resets (including post-DFU soft resets) are misclassified as button presses
• The issue persists even after power cycling the device

Question:

1. Does DFU leave different register states than SWD programming?

Thank you

[Hieu]

Hello luqman,

I expect that in most cases, DFU would reset the device with reason Soft Reset. However, depends on the exact strategy, it can differ, for example, if it requires a manual reset from the end user.

What reset value are you having? From the code you post, I see that anything other than reset reason DIF or no reason detected will fall under the else clause. That is quite a many different reasons...

Please refer to the RESETREAS register documentation: https://docs.nordicsemi.com/bundle/ps_nrf52840/page/power.html#ariaid-title35.

I also recommend consider using the nrfx driver or HAL layer to get reset reason for better code readability.

Hieu