How to see LOG in Bootloader if app moves into bootloader ?

Hello, Nordic.

I use SDK15.3.0, s340 softdevice, nrf52840.

Recently, I am testing dfu service. So I merge App, softdevice, and bootloader.

Dfu service's test has done very well. 

But I don't see any Log in bootloader. I also use pca10056_ble_debug and NRF_LOG_ENABLED is 1. So I think I must have seen any log in bootloader.

If you know any way, please let me know how to do that.