After I realised Tezxas, I think about IBM PC emulator for TI89 and TI92+, using similar technics.

Assuming that we have 256 K of memory, about 90 K will be required for emulator itself, original video memory, emulated video memory and conversion tables. I have idea for fastest possible instruction interpreting loop.

This means, we can emulate IBM PC with 128 K RAM. It was, in that time, really good machine.

However, as TI89 uses a big part of the memory for own purposes, exiting from program will be done from reset.
This means that emulator will be for AMS 2.xx only.
Alternativelly, it can be flash application, but a bit slower because it can not use selfmodify code.

Flash memory can be floppy drive, formatted to 320 K,
remaining memory is for copy of emulator itself. Format will be - one TI89 file - one PC sector.

BIOS functions will be executed in native 68000 code..

Estimated speed is IBM PC/2.5 MHz. About a half speed of original PC/XT.

Emulated devices will be keyboard, screen and floppy.

Video card is MDA, textual. On TI89 we can show picture from four corners /or in scrolling window/ where character matrix is 4x8. On TI92+ we can show full picture with matrix 3x5. We can think about CGA graphic modes too.

Caldera Open DOS 7 is version of DOS with source. We can reduce it in size by removing some unnecessary functions, or find somewhere MS DOS 2.0 (unfortunantelly it is pirating).

However, there is not so much software that can run on this configuration. Maybe first versions of Wordstar, Lotus 1-2-3, Turbo Pascal, many command line compilers and dozen of shareware utilities. In case of graphic mode emulation, also we can expect that oldest games as digger will work.

This can be very cool project, but requires a lot of work and some people can join to it.

Comments?

This sounds like a very cool project. Actually accomplishing it would be an amazing technical feat. However, I do not see the usefulness of it. Tezxas is useful because it allows one to play many, many great games on the 89/92+. There weren't very many games for the original PC that ran in text mode that would be well suited to be emulated on the 89/92+, that couldn't be done better natively, and much smaller. The PC as I'm sure you realize is a very complicated environment to emulate, especially when you have to write the entire BIOS yourself. You mention Lotus 1-2-3, WordStar and Turbo Pascal. Native versions of these programs would be much more useful. Writing a native version of all three of these could probably be done in less time than making them work, well enough to use, on the 89/92+. Tezxas is very impressive, and a PC emulator even more so. But it's not very useful.

What I would like to see for the 89/92+, that would be useful, would be an a z80 calculator emulator. The 86 would be the calculator to focus on, since it has arguably the best games, can emulate most games from the other z80 calcs, and for most good games that it can't emulate (the latest YAS does just about everything), there are native ports.

For a lot of stuff, like physics, I find my 86 easier to use than my 89. The menus are a lot simpler, and the unit conversions are easier to get to. Not that the 89's symbolic math features don't have their advantages, overall, I find the 86 to be a better calculator (the fact that every assembly program for it will run on any calculator without any additional software says a lot). The 89 has more than enough room to store the 86's RAM and ROM, with some extra space for the really good 89/92+ programs like TI-Chess and Phoenix. Plus, the keys map directly, and the display is big enough to not have to scroll. Being able to push a button and have the 89 switch into an 86 would be pretty damn cool :)

You already have the Z80 emulation written, so it's not like writing a whole new emulator (I know, that's half the fun). I don't know what kind of speed you are getting out of it, instruction for instruction, but I'm sure it's more than fast enough for the ROM to be usable, and most games ought to be playable. I know the z80 calc's hardware as well as anyone, and would be happy to help out on this in any way necessary.

Btw, any plans to release the source to Tezxas? I would love to see it, and if it were available, I might start in on this project myself :)

I promissed to release Tezxas source after receiving POTM award for Tezxas. I have got the award, finally, and source will be soon released, maybe with GPL license. However, source is very tricky, because the goal was to make fast, not nice looking or portable program. I must spend one weekend to comment it.

By the way, I have source of on PC emulator for UNIX, It is in C, but contains code for BIOS routines.

bug: if you're on a bridge overlooking a waterfall (?), and then jump off... you'll be stuck in a never ending series of vertical screen scrolling. heh, i killed my friend's calc that way. :)