Well that's nice. Can't wait to see this on the other 83+ calcs. And that would allow for custom boot code?

This won't work on 83+'s because on those, TI most likely locked the boot code the proper way with the flash chip itself. Here is the only reason that it actually works on an 84+: (new paragraph so people can quote me )

On the 84+, for whatever reason, TI decided not to hardware write protect the boot code sectors. The flash chip supports this feature, but TI didn't do it. So TI just programs the boot sectors and puts the flash chip in the calculator. That was mistake number one, but here comes mistake number two. Next, probably in order to save money, TI decided to make the circuit boards of the 84+ and 84+SE exactly the same, the only difference of course is the flash chip. So, to make sure that the boot sectors can't be overwritten, TI had to come up with a way to block different sectors on the flash chip for each model even though the hardware was exactly the same. Their solution was to make a port on the calculator that protects different flash pages based on its value. And finally, since the boot codes were programmed differently on the flash chips, TI put in code to set this port to different values based on the size of the flash chip. This way, as long as no one touches that port, the calculator will look like the boot code is write protected. However, we discovered what this port was and removed their boot code protection.

After writing this, I feel like this would work on the 83+SE also.

(Now, after all of that, if you know a bit of assembly, I'm sure you can figure out how to do it.)

I didn't say you could do it, I just said you know how to do it. Or you at least have some ballpark idea.

Quote from: Deep Thought on June 27, 2011, 01:09:58 pm

So we can boot Windows Vista now!

* Deep Thought runs

You better run fast =]

Anyway, that's amazing news.
Just hope noone will be legally hurt after this discovery...

I believe any threats they sent would be totally unfounded, and probably just ignored. It's fully legal to replace code on your own device, as long as you're not replacing it with unlicensed copyrighted code.

TI has essentially no legal case in this situation. Even if they wanted to go after BrandonW or thePenguin (which I doubt they do), they can't make a case against this. For once, the law is actually in our favor here because this hack allows us to actually remove all copyrighted code from the device. Previously, TI could have made a [tenuous] case against all 3rd party OSes because the boot code was still present.

If and only if new OSes also overwrite the boot code. Needless to say, that's not exactly a desirable thing, for reasons previously mentioned by thepenguin77. However, I think the danger of the process could be somewhat mitigated if someone wrote a good alternative boot code and open sourced it.

Call me a n00b, but what's the function of the existing boot code?

I believe it is the code for loading the OS(guess)

It's also able to receive new OSes over I/O and USB. Kind of important.