nRF takes a long time 3-6 minutes to boot

[Andrew Ong]

I have two boards. I ran the exact same commands on both boards. The commands flash the same bootloader+app+softdevice+app settings hex file. One board reboots into the application only once, while on the other board, I can reset the application as many times as I want in the RTT. (by pressing "r" then "g") What could be the problem here? Why is the boot behavior different? 

nrfjprog -f nrf52 --eraseall --snr 260102227
nrfjprog -f nrf52 --snr 260102227 --program ./bin/nrf52_ble_app_release_v4_2018-10-05T02:38:23Z.hex
nrfjprog -f nrf52 --reset --snr 260102227

[bjorn-spockeli]

It is possible to place the Segger RTT control block at the same location in RAm for both the application and bootloader. Then you do not need to reconnect after the bootloader jumps to the application. See this case for the instructions:

https://devzone.nordicsemi.com/f/nordic-q-a/30310/easy-way-to-merge-bootloader-and-application-rtt-output

[Andrew Ong]

But this is not about whether RTT connects to my application. My application does not start at all. There are LEDs on the board that turn blue when the application starts. On one board, it takes many minutes for them to turn blue and on the other, they turn blue instantly. I was wondering if there is something like the GPREGRET register in the secure bootloader that makes it wait there for many minutes. 

[bjorn-spockeli]

The Secure Bootloader will remain in bootloader mode upon start up if the GPREGRET register or the bootloader button pin(Pin 16) is asserted, see dfu_enter_check() in nrf_bootloader.c. You can try to debug the bootloader to see if it starts the application or remains in bootloader mode.