u-boot-nintendo-nes-classic-edition 2018.11 ARM bootloader
U-Boot is a bootloader used mostly for ARM boards. It also initializes the boards (RAM etc).
This version is for the Nintendo NES Classic Edition. It is assumed that you have added a serial port to pins PB0 and PB1 as described on https://linux-sunxi.org/Nintendo_NES_Classic_Edition.
In order to use FEL mode on the device, hold the Reset button on the device while it's being turned on (and a while longer).