Okay I heard OS2.55MP is bad for basic progs, so I decided to downgrade to an older OS (2.43) but I ran into a problem: I didn't uninstall zStart's run on ram clear first. I screwed up big time and now it won't downgrade. I send it 2.55 and it stops at validating 100% and goes into an infinite loop. It says transfer was successful on my comp but I can't do anything but a battery pull after it says success to get it to do anything. The only thing it does is wait for a new OS! Help? I tried holding Vars and Clear!

When you turn it on, does it ask for an OS? If not, send it an OS and unplug it in the middle of a transfer to invalidate the OS.

Battery pull, hold mode, and reinsert the batteries. This should have it erase the flash. The numbers counting up are how many times it erases it, one is enough. (Is mode the right key?)

Send it an OS. If it still fails, then the certificate is bad. I have no experience with that...

Mode is the right key. It simply takes an extremely long to validate and I was unplugging it during the process, and it doesn’t ring an error when that happens and it invalidated it. Several times. I just need to get to zStart, because it throws a ton of RAM clears my way and I can’t get it to just work like I want it to.

I've heard that with some of the newer OSes validation takes a whole 7 minutes, which is frankly unacceptable as far as I'm concerned.

Took me about 10, Kerm. It’s unholy, sacrifice is inevitable. I validated my 83+SE faster than a flash app.

I'm sure someone has tried this, but can the boot code, older version, run on the newer models? I mean, we can nuke and rewrite the boot code...

You'd probably have to rewrite the certificate, as I'd assume they no longer ship the cracked keys. In fact, merely rewriting the certificate may be all you'd need, as it probably maintains the ability to validate smaller signatures, since those would be needed to validate apps.

Doubt it. f I recall, the OS and app keys are different. You need to either use flashy, w/e, to manually install an OS, or just rewrite the boot code and certificates (I don't think and hardware was changed to prevent that).

Yes, the OS and apps use different keys, but my point is that they now also have keys of different sizes. Unless the validation code special-cases OS keys to be larger, there should be a way to craft a smaller OS key which can be used to validate OSes, as I'd assume the crypto code is generic enough to be used on arbitrary key sizes. It's simply a matter of finding the right format to indicate a short OS key.

Actually rewriting the boot code is the proper method and iirc there is also an exploit to get the existing boot code to only use the old Validation method by modifying the OS file.

That said if you have one of the newer calcs that does the long validation a stock TI-OS 2.43 doesn't include the extra signature so no matter how many times you try it will not validate. BrandonW would know the specifics but I'm not sure if he posted the info anywhere.