Operating System on NVMe (without SD Card)

TL;DR - HOW CAN I BOOT DIRECTLY FROM USB with NO SDCARD QUESTION:

Hello from sunny Tucson, Arizona, US. I’m still working on one script to go from SDcard to FDE (Luks) and I’ve run into a problem.

I’ve Google searched and don’t see the answer… or perhaps I see the answer and don’t like it.

I want to boot my Reform2 from USB without an SDcard or NVMe device present. I am currently unable to figure out how to do that, and the documentation on the boot process is sparse, as in ‘the script does X’ but not which script, or who called it, or where it all got started.

I’ve done the Google search. I’ve looked at /boot/dtbs and the .scr files. I haven’t cloned the whole archive because it seems to me that things like ‘u-boot’ are separate from the ‘reform’ stuff. I did download the ‘new’ u-boot that is supposed to be able to boot from everything, but without the SD card and NVMe it won’t boot.

I have loads of SD cards, and a couple of NVMe ones. This is about solving a general long-term need, not anything immediate. If I can’t get it to work… I’ll try different hardware.

Unrelated to the question, other things on my mind when hardware is being discussed…

Hardware Project #1: I’m not messing with the NVMe until I get my SPST DIP switch and wire an external switch so I only have to open the case, pop the batteries out, and undo the heatsink ONCE. Still I’d rather SOLVE the USB issue before going to NVME. (Yes I know I could use NVME and have u-boot on that go to USB just as I’m doing now with SDcard, but I’d rather rely on NOTHING other than that USB stick…)

Hardware project #2: Add a DPST switch to allow disconnecting the batteries without opening the case.

Hardware Project #3: The USB ports are 2.0 and upside down. It would be nice to add a USB3.1Gen2 aka USB3.2. I’m not knowledgeable enough about this virtualized chrooted system’s compatibility with that goal tho, so for now that’s just a dream. Josch has a great post at Adding LTE Modem and other USB devices - #6 by svp about adding a USB hub in the case, and he makes reference to the Nanohub which now offers 4 ports for $20 USD and fits in almost any space.