If you running old version of U-Boot without R&D mode, it should reboot your device after few seconds. It is because old version does not have implemented watchdog kicker and when device is not in R&D mode with disabled watchdog, hw reset device. New version, of cource, has this problem fixed.

fiasco-gen is program which generate fiasco images. Flasing kernel (or other part) can be done also in device without PC. But it needs to be in fiasco format. So this is reason why kernel(-power) generate fiasco image.