I've finished the link routines, and they work very nicely but I know there are slight differences between the hardware and I need to make sure I am leaving enough room for variations.  To make the routine as fast as possible and therefore usable in realtime games that have a lot of data to send, the routine is time based instead of confirmation based.  There is a minimum threshold of 10 T-states (1.7 microseconds) which is enough to give me 100% error free byte sending on 2 linked 84+'s and should be enough between all z80 calcs, but unfortunately the Nspire emulation is too slow.  Not sure if there's anything I can do about that.

Anyway, I just need to confirm that this works.  If you have an I/O cable and 2 calculators, preferably 2 different types for example: TI-83+ and TI-84+SE, then please help me test this.  The receiver should run program A which just relays to the screen and then have the other calculator run program B which sends a random byte.  Make sure both the numbers are the same on both calculators and repeat a bunch of times and then switch the roles of sender and receiver.

If there is an inconsistency, let me know which calculator was the receiver, which one was the sender, and the numbers that show up on each screen, thanks!

Well, those with Ndless might have access to a better emulator in the future so that could actually be an advantage.  However, you can still link an Nspire with another Nspire if they're both running the same OS version since I think the speeds would be close enough in that case.

If only I had two calcs... And yeah, too bad that we've been unable to discover how to work the link port.
Good luck with the routine, though!

Thanks ztrumpet!  I'm working on fixing them right now.  Those results are kind of interesting.  Seems the 83+ never failed as the receiver and most of the errors were bit shifts.  That probably means the receiving routine is a little too fast.

Yeah, this is for the I/O cable only.

USB linking is incredibly complicated.  I don't think its ever been done before in a game, the routines would be MASSIVE and the speed would be way too slow for anything realtime.  It doesn't help either that TI never documented any of the USB functionality so all the information we currently have on it is from hackers and disassembly.

okay, so probably it's never gonna be implemented? or could it be done in the far future perhaps? I would appreciate it very much, since the most of the people in my area have a 84+, without a I/O cable (just like me)

I think 83+'s still come with I/O cables, but I believe that 84+'s come with a mini-USB to mini-USB cable.