Is it possible to stop TIOS from modifying certain flash pages? It was suggested that I mark them as having apps on them. Would that be messed up by defragmentation?

That's a good question. I'm pretty sure that during the defragmentation process, the TI-OS examines the 128-byte (or is it 256?) (no, it's not) header on each page of each app. You could fake your app pages to make it look like one big contiguous app, which would probably prevent the TI-OS from separating them, but probably would NOT prevent it from trying to move it.

Perhaps it is possible to make it look like a single, enormous app. Would it show up in the app menu, and the memory menu?

At the beginning of the sector, you have a status byte... Setting it to 0xFC, 0xF0, 0xFF marks it as valid, but I don't know what the other bytes will cause the OS to do... You may want to poke around here, but just a thought

Which I just said. I'd imagine that it would indeed show up in the app and memory menu.

iirc, someone once said that you can't hide apps the same way you hide programs (first character minus 40h). So I don't think there is a way to hide them :/

Correct, you cannot do so. Remember that whole topic about increasingly awkward ways to hide Apps?

Sector headers only apply to the archive. The first byte of a sector has no special meaning for applications, and applications can cross sector boundaries. Applications and the archive cannot share a sector.

You can mark multiple sectors as being swap sectors. It's possible that if you do that, TIOS will only use the first sector marked as a swap sector, and ignore the rest, showing their space as being absent, and not erasing them during garbage collection.

It's possible but not definite? SirCmpwn, sounds like you just need to do some experimentation based on your educated guesses. .

(Epic bump). From my notes about dual booting OSes, are there any parts of TIOS that do not base the model off of port 0x21? If I can modify that port and fake TIOS into thinking that the calc's flash chip is smaller, I could shove in some code to get 2 OSes working.

I don't know if there are other ways used by TIOS in getting flash sizes, so...

Still won't work without weird hacks. You might clone the certificate and boot code to a lower page, but then very bad things will happen when it goes to erase one of the certificate sectors, as those are unique in that they're half the size of the other flash pages.

When would t clear those pages? Only on OS transfer?or...

IIRC, there are all sorts of poorly-justified reasons for it to muck about with the certificate. I want to say it even goes erasing and rewriting the certificate sectors when validating a freshly-received app, but not sure about that.

What exactly does it do to the certificate? If it tries to read/write on it, would it be possible to intercept writes/erases to the page? I am sure that whatever call is used can be modified to check the target pages first