Excellent questions, and yes I’m aware that it doesn’t boot from the USB directly. Full answers below, but first thank you for continuing to help me learn this.
It is frustrating that the documentation isn’t sync’d so one source ‘get X from here’ and the other says ‘build X from other-here.’ There’s no unified “one place that leads to all others” that is always correct. This is where the ‘arch’ community really has everyone else beat… which makes it easier for new entrants to get up to speed without falling into rabbit holes.
Numbered TL;DR:
- Boot from SD. SD originally continued as is with dd’s sysimage and when done all partitions were on the SD.
- Now /boot still on SD but it then mounts / on /dev/sda1 on usb. Works fine
- Attempting to return to state 1 (SD only) results in a black screen.
- If you’re saying I must get a UART cable and another laptop and can’t get any useful feedback via either mini-OLED or HDMI screen, I guess that’s one more thing to buy.
E:
DIP switch ALWAYS is in the SD position from factory. I won’t remove the heatsink until the new thermal paste arrives in two days. (No local electronics store exists 
)
Uboot version - not sure how to get that so the answer is “whatever is in the newest system image I dd’d to the SD card.”
Version of boot.scr (unkown):
dumpimage -l boot.scr
Image Name: boot script
Created: Thu Oct 6 07:13:44 2022
Image Type: AArch64 Linux Script (uncompressed)
Data Size: 3124 Bytes = 3.05 KiB = 0.00 MiB
Load Address: 00000000
Entry Point: 00000000
Contents:
Image 0: 3116 Bytes = 3.04 KiB = 0.00 MiB
Kernel:
uname -a
Linux reform 5.19.0-reform2-arm64 #1 SMP Debian 5.19.11-1+reform20220925T130929Z1 (2022-09-25) aarch64 GNU/Linux
<.code:
initrd/initramfs:
ls -al initrd.img-5.19.0-reform2-arm64
-rw-r–r-- 1 root root 33550480 Oct 9 19:10 initrd.img-5.19.0-reform2-arm64
sysimage-v3: I have not built a system image myself. I’ve used only the ones available on the mnt.re website… which may not be sysimage-v3 BECAUSE if you go to MNT’s website at mnt.re it says you can download the sysimage-v3 prebuilt at this link but that is a 404.
So I’m guessing I don’t have that sysimage-v3. Cloned the git repo to build it. About 1200 apt packages inbound later. This is a software disaster. Irrelevant packages needed by other irrelevant packages need by real packages are being downloaded and bloating the filesystem. I should probably go back to sleep. Kicad? libgweather? libspeech? liinphone? These are necessary to build a system image? /smdh
After an hour and a half mkimage.sh reports device is out of space. Unbelievable. Definitely time to go back to sleep. If I can’t build one lousy image in 120GB of space, the process needs fixing.
Ehud