For anyone interested, I'm working on making this myself.
Plan to share when done.
This is a major project - I've been full-time on it for 6 days so far.

@WereCatf Can you share the console command to get the wifi to work?

I built and installed my own lede-ramips-mt7688-omega2p-squashfs-sysupgrade.bin - which works fine, except of course for wifi...

My rough goal is to share a working SD card image for the omega2+ which has the complete build system on it, to hopefully get rid of the interminable missing headers and other random dependency roadblocks that I and many others keep hitting!

MIPS32 have a unique CPUID I think? This sheds a bit of light: https://en.wikichip.org/wiki/mips/prid_register

Try raising a support ticket. They did reply to mine, so they are there and doing stuff.

Mine on same fw works:-

'# which reboot
'/sbin/reboot
'# dir /sbin/reboot
'lrwxrwxrwx 1 root root 14 Feb 2 2017 /sbin/reboot -> ../bin/busybox*
'# md5sum /bin/busybox
'ea6470f444af811d7866f825e27bfb54 /bin/busybox

Loads of things cannot be installed owing to missing header files and other dependancies, which are normally overcome by having the development versions of packages installed.

Can someone point me to the source and/or "-devel" versions of the things that can be found in the opkg repos ?

For example: DBD-mysql needs the mysql headers, loads of things need kernel headers, a non-crippled "ps" build requires ncurses which requires a missing stdc++ lib and so on down the dependancy tree.

Alternatively, how do I get a copy of the entire source for the onion distro and o/s with instructions to rebuild everything?

For anyone interested, I'm working on making this myself.
Plan to share when done.
This is a major project - I've been full-time on it for 6 days so far.

I want to build ON the omega itself, preferably in busybox. I'm not interested in cross-compiling.

Can someone please share an image for this with a working toolchain, preferably with plenty of related other tools etc already installed and working (e.g. LAMP), demo code, etc.

I am midway through creating a USB version of this for Ubuntu (which I will share if it works OK), but I would prefer busybox if anyone can help!

needed the below to work on my USB drive:-

mkswap /dev/sda2

All - I owe a HUGE debt of gratitude to your detailed answers.

Since it does seem the weight of consideration, as well as design (including at least DMA and cache), is going to be fighting against me, I'll head back to the drawing board and find something more architecturally suitable for real-time work!

I feel like I owe you all at least a beer - your patient explanations have almost certainly saved me months of headache.

Thanks @luz & @Zheng-Han !

During the "duty" of my application, I do not need any O/S support; I merely need to run machine code (which makes no O/S calls), access small amounts of memory, and and accurately control the output timing of my signals (with no exceptions). Normal "duty" would mostly be 10's of seconds, sometimes 10's of minutes, and occasionally as long as 2 hours nonstop - but always ending with enough time to re-enable interrupts and let the O/S service anything it might want to do, before (hopefully) allowing my code to make a couple of O/S calls to (for example) update some files from the stats accumulated in it's memory.
"End of duty" times would always be many seconds at least. I do not need to keep track of time.

So yeah - while I don't need any O/S for my main purpose; it would be nice to have it available "in between" duty times for other purposes, like displaying stats, doing updates, and so on.

My purpose for "bit bashing PWM" is confidential (sorry!) but suffice-it-to-say, it is non-linear, non-conventional, non-constant, and "human safety critical" - battling other peoples code and hardware to try and get my application to work with existing tools will be too much work and too high safety risk (one unexpected interrupt doing something unusual could have catastrophic consequences). Or in short: I need "real time" for my code, in the old-school genuine meaning of that phrase.

Do you guys believe the O/S would really "crash" like that Marc guy said? Nothing can "crash" when it has no control - I can't figure out if he's smart or stupid, because he says a mix of both things in his answer! (e.g. "nice" is irrelevant, but he seems to know that, and "Waste electricity" is just plain insulting)