Trying to understand the function of the buttonless_dfu_sdh_state_observer() in ble_app_buttonless_dfu example

[TomKeddie]

The buttonless_dfu_sdh_state_observer in this example is shutting down the cpu when the softdevice is disabled using an observer. 

static void buttonless_dfu_sdh_state_observer(nrf_sdh_state_evt_t state, void * p_context)
{
    if (state == NRF_SDH_EVT_STATE_DISABLED)
    {
        // Softdevice was disabled before going into reset. Inform bootloader to skip CRC on next boot.
        nrf_power_gpregret2_set(BOOTLOADER_DFU_SKIP_CRC);

        //Go to system off.
        nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_SYSOFF);
    }
}

/* nrf_sdh state observer. */
NRF_SDH_STATE_OBSERVER(m_buttonless_dfu_state_obs, 0) =
{
    .handler = buttonless_dfu_sdh_state_observer,
};

I'm not sure why this is necessary in a dfu implementation.  Our app has this observer in it copied from the example.  When I disable the softdevice it triggers this method and shuts down the cpu when I don't want it to.

ps. nrf52832, sdk 15.3, s132

[Amanda Hsieh]

Hi, 

Basically we will try to disable softdevice before we enter deep sleep mode (System OFF) to be able to write to GPREGRET2 retention register that the bootloader doesn't need to check CRC.

You can remove this implementation it's not really needed in your case. 

Please also see this post. 

-Amanda H.

[TomKeddie]

Thank you, that makes sense.