@Igor well I'm not getting very far, unless I'm prepared to count failures... I have more of those.
The SD Card reader / writer works well; I can use it to carry out various operations on my brand-new SanDisk Extreme Pro A2, including formatting from the Ubuntu Disks application, running SDCardFormatter, using usbimager to create the Armbian 25.5.1 Noble Minimal system disk, mounting, unmounting and ejecting... When I've finally got the SD card set up, here's what the Ubuntu Disk application shows. Note the first partition is 4.2MB of free space.
When I put this SD card in the Cubox and boot from it, the same thing appears to happen as previously - on the HDMI-connected monitor, the Cubox bootloader runs and hands off to the boot program, after which the monitor reports no HDMI signal and the monitor goes into sleep mode. After approximately two minutes, the Cubox bootloader appears again on the monitor, hands off to the boot program, and... the same thing.
Nothing seems to be active at the IP address - I can neither ping nor ssh to it.
This time I have my laptop connected vi USB to the Cubox console port. Various positive messages show up in
dmesg
finally ending in:
usb 1-6: Detected FT-X
usb 1-6: FTDI USB Serial Device converter now attached to ttyUSB0
But running either screen or minicom, they return immediately, showing no sign of having established any kind of connection, no waiting for a connection, no error message, nothing.
Just a reminder that this Cubox boots and runs fine on the current system SD card which is up-to-date bookworm minimal.