Hey guys, I'm still putting some finishing touches on NESizm but I sense that I am closing up shop on it pretty soon.

I've decided my next project will be emulating some of the older TI calculators based on Z80, directly on the Prizm. A calculator within a calculator! While I am specifically targeting TI-86 (for nostalgia: https://www.ticalc.org/archives/files/authors/59/5996.html ) and TI-83+ (for the legacy).

I think it should be initially pretty easy to get this up and running, compared to NES and GB the hardware on these is quite simple. As an added challenge, I may try to get assembly programs working directly within the emulator w/o an available ROM file. This would help people play the games made by the community w/o having to own an original calculator in order to get a ROM file, and help preserve the legacy of some of my favorite games growing up.

Yes, the eZ80 and 84+ CE is quite possible, but not a priority for me right now with this project because I am more interested in the older stuff

Does anyone have particularly calculator/game they'd like to see working?

That's a great project idea

For the 83+ family, nearly all assembly programs use OS BCALLs, and emulating the OS properly requires several bytes of the boot code. Of course, you could use FreeBoot, which contains only those bytes, without the rest of TI's boot code.

If you're looking for another project after a TI-Z80 emulator: proper emulation of the TI-68k series' official OS ("AMS"), or PedroM, does not require the boot code. Importing an AMS or PedroM OS upgrade file into a fake ROM image is simply a matter of generating several data bytes ("Hardware Parameter Block") which are located in the boot code area, and having the reset vector + initial SSP point to values which are effectively hard-coded, respectively ROM_base + 0x12188 and 0x4C00, though they can be gathered from the OS image, usually ROM_base + 0x12088, 0x1208C.

For the non-ROM version: The plan is to just intercept the BCALL instructions and implement their functionality directly in C. I could theoretically have the emulator load up the .8xp files right out of ROM from there. The roadblocks would probably just be learning all the ins and outs of the system call results themselves, making sure the results were cycle accurate, etc.

PedroM does seem like a good target though. Emulating the 68K would put me a lot closer to a potential Genesis/Megadrive emulator. I guess my hesitance is that I have and have worked with both the 83+ and 86 a lot so I feel a lot more confident.