DFU: nRF51822 OTA bootloader jams after reset_prepare()

Question

I managed to upload my application OTA DFU when there was only the bootloader running. After my application is there, I can start DFU and my application runs thru reset_prepare() function as expected. However, it seems that it never enters the bootloader although DfuTarg seems to appear as an available BLE device. So I cannot upload my application another time :( 
 Any ideas what could be wrong? Why my application does not start bootloader (correctly) after reset_prepare()? 
 EDIT: The bootloader enters event loop and jams there, see the code below (from bootloader.c/nRF51_SDK_8.0.0_5fc2c3a). The DFU loader at phone side says "disconnected" (mostly, sometimes it jams). I cannot reconnect although DfuTarg is visible. 
 for (;;)
{
 // Wait in low power state for any events.
 uint32_t err_code = sd_app_evt_wait();
 APP_ERROR_CHECK(err_code);

	myLedIndication(); // This shows me bootloader is running here very busy

 // Event received. Process it from the scheduler.
 app_sched_execute();

 if ((m_update_status == BOOTLOADER_COMPLETE) ||
 (m_update_status == BOOTLOADER_TIMEOUT) ||
 (m_update_status == BOOTLOADER_RESET))
 {
 // When update has completed or a timeout/reset occured we will return.
 return;
 }
}
 
 And the reset_prepare() looks like: 
 static void reset_prepare(void)
{
	uint32_t err_code;
	if (m_conn_handle != BLE_CONN_HANDLE_INVALID)
	{
 // Disconnect from peer.
 err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
 APP_ERROR_CHECK(err_code);
 //err_code = bsp_indication_set(BSP_INDICATE_IDLE);
 //APP_ERROR_CHECK(err_code);
	}
	else
	{
 // If not connected, the device will be advertising. Hence stop the advertising.
 advertising_stop();
	}
	err_code = ble_conn_params_stop();
	APP_ERROR_CHECK(err_code);
}

Jarmo · Accepted Answer

I am now using a dirty hack to get rid of bootloader jamming. The modification is at the bootloader's main.c, and it makes the bootloader to reset after it first enters from application, and only after that, it enters the actual bootloader code. However, two upload tries is now needed from nRFTools, so the solution is not optimal. 
 bool app_reset = (NRF_POWER->GPREGRET == BOOTLOADER_DFU_START);
bool app_reset2 = (NRF_POWER->GPREGRET == ~BOOTLOADER_DFU_START);

if (app_reset)
{
 NRF_POWER->GPREGRET = ~BOOTLOADER_DFU_START;
 NVIC_SystemReset();
}
else if (app_reset2)
{
 NRF_POWER->GPREGRET = 0;
}
 
 In addition, few other changes are needed to support "app_reset2" (several places at main). At least it works now somehow. But it is really a dirty hack as I said...

DFU: nRF51822 OTA bootloader jams after reset_prepare()

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