Third-party firmware PoC...

[debrouxl]

At first, I didn't change the values of the LCD controller registers, and nothing was displayed on the screen - but it might have been because of a blunder elsewhere, and maybe my setting of the three main registers (start, end, size for window 1) does more harm than good after all. I'll check again later.

I fully agree about the usefulness of making a hardware ports dumper. That's precisely what was done with the Nspire CX (CAS). At first, on the Prime, the data should be displayed on the screen (we already know how to do that), so itoa + A1R5B5G5 sprite routines + font data are required. No biggie, but I won't have much time until Friday, at best...
Other people should join the fun

OT: wait... you're one of the developers of HPGCC(3), among other things, aren't you ?
I used to be a contributor to the dead TIGCC, and I'm the GCC4TI maintainer, even if I'm basically doing nothing anymore, because TI-68k native code programmers have been very few, for several years.