Bislang ist es mir nicht gelungen die Firmware-Version zu ändern, wird scheinbar irgendwo intern ausgelesen.
Rename the firmware to "Elgato_UAB_Boot_Image" and place it on a FAT32 formatted USB stick. Plug it in to USB port and reboot. The device should boot firmware from USB stick. This won't leave any permanent changes to NAND flash, so if You want to go back, simply remove the stick and reboot.
I would suggest connecting UART<->USB adapter to UART pins which are populated on J24, (I have the first version with 2 USB ports, might be different for newer one with single USB port), don't connect the first pin:
ZIM-1900 VER:1.0
J24: 1. VCC 3.3V, 2. TX, 3. RX, 4. GND
^
After connecting terminal You'll see also messages from bootloader. If USB is inserted there are these messages:
***** USB AUTO FLASH *****
SPI image Elgato_UAF_SPI not found
SPI image Elgato_UAF_OTP not found
Partition image Elgato_UAF_Boot_FW1 not found
Partition image Elgato_UAF_Boot_Loader_0 not found
Partition image Elgato_UAF_Boot_Loader_1 not found
Partition image Elgato_UAF_UBoot_Env not found
Partition image Elgato_UAF_Linux_Kernel_0 not found
Partition image Elgato_UAF_Linux_Kernel_1 not found
Partition image Elgato_UAF_AppFS_0 not found
I didn't test these yet, but I assume each will replace corresponding partition contents on NAND flash.
When I fiddled with the device, my goal was to put Tombea on different ports and block external access to them with iptables, then add minisatip as a client and use that as a server. Unfortunately I had limited time and with none sat cable available (have to change my sat installation) I had to postpone it indefinitely. Along the way I created a very crude build system, which would create a full firmware initramfs ready to be copied to USB stick. The build system needs rpm<=4.15.x, yum and yumbootstrap to create Fedora 8 chroot. The scripts are in attachment. Maybe You'll find some inspiration out of it. The flow of execution is:
1. prepare-source.sh, 2. sudo prepare-chroot.sh, 3. build-firmware.sh