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Qwerty.55 wrote:
It's an actual CRC-16, as far as I'm aware.
I assume you guys already checked the five common CRC-16 polynomials listed here?

http://en.wikipedia.org/wiki/Cyclic_redundancy_check#Commonly_used_and_standardized_CRCs
Er, I hadn't, but after checking them, it would appear that none of those work.
Qwerty.55 wrote:
Er, I hadn't, but after checking them, it would appear that none of those work.
Rats, that's unfortunate. Sad Three is hardly enough to solve a polynomial of both unknown degree and coefficients; I wish we had more samples.
Would a brute force crack be possible? There are only 2^16 possible polynomials and we know the inputs.
Qwerty.55 wrote:
Would a brute force crack be possible? There are only 2^16 possible polynomials and we know the inputs.
But imagine the time necessary to load 65,535 add-ins to your Prizm and see which one works.
I meant on a computer. The CRC algorithm is the same. The only thing that's different is the polynomial, which means that you should be able to increment a hex word and keep computing the CRC until it matches the observed one.
Qwerty.55 wrote:
I meant on a computer. The CRC algorithm is the same. The only thing that's different is the polynomial, which means that you should be able to increment a hex word and keep computing the CRC until it matches the observed one.
But it's a CRC of the entire add-in, is it not? If you have something like 16 degrees of freedom, then you could come up with near-infinite valid solutions. Perhaps I'm missing something.
It's a CRC of the checksum of the entire add-in, not the add-in itself. That's how we're able to run code. It's just a matter of keeping the checksum the same. But isn't the polynomial a halfword such as 8005?
Qwerty.55 wrote:
It's a CRC of the checksum of the entire add-in, not the add-in itself. That's how we're able to run code. It's just a matter of keeping the checksum the same. But isn't the polynomial a halfword such as 8005?
From Wikipedia: "17 bits (CRC-16)" Still, there are near-infinite ways to get a specific CRC from a specific checksum unless we have a certain amount of samples to rule out false results.
That sucks. I suppose we'll just have to wait for more add-ins then.
Qwerty.55 wrote:
That sucks. I suppose we'll just have to wait for more add-ins then.
I suppose so. If we could narrow down the space to something sane, it would hopefully be possible to try a handful of add-ins on-calc to narrow it down to the one solution. Of course, it would be faster to find the CRC checking code somewhere, either in one of their computer-side programs or in the OS.
KermMartian wrote:
Of course, it would be faster to find the CRC checking code somewhere, either in one of their computer-side programs or in the OS.
There's no computer program that deals with add-ins, so we're stuck with the OS.
We're probably not going to find it in the OS for quite some time (without I/O at least). There's a lot of code in there and very little of it was written in any sort of sane fashion. Either their compiler or their programmers lumped the data into huge blocks and used a ton of spaghetti code. The only thing that doesn't appear to be a bunch of consecutive subroutines is their Interrupt code.
Qwerty.55 wrote:
We're probably not going to find it in the OS for quite some time (without I/O at least). There's a lot of code in there and very little of it was written in any sort of sane fashion. Either their compiler or their programmers lumped the data into huge blocks and used a ton of spaghetti code. The only thing that doesn't appear to be a bunch of consecutive subroutines is their Interrupt code.
Ugh, sounds painful. Sad And there's no real hardware emulator yet, correct?
Renesas has technically made one, but it runs on C code.
Qwerty.55 wrote:
Renesas has technically made one, but it runs on C code.
I think I misunderstand what you mean, because I wouldn't generally care in what language my emulator is written. Wink
Not to spam and start a meme invasion on the site, but as Prizm hacking is continuing, and in reference to Qwerty.55 almost frying his calc a few times, I could not resist leaving this grammar fail alone. Shock



This is a secret debug menu available by pressing the reset button at the back of the calc, then holding down OPTN, EXP, AC/ON and releasing the reset button while still holding down the other keys. This appears, then if we hold the MENU key for a few seconds, we see the following options until we release the MENU key:

Quote:
[F1]: Erase User Flash Area // Clears user flash memory
[F2]: Erase Password Area // Removes user name and organization
[F3]: Erase MCS Backup // Clears user RAM backup on the flash
[F4]: Erase Add-in Language // Removes language add-ins
[EXIT]: Flash Program // Purpose unknown


Since I am not tech-savy, I took no chance, though, because I did not want to wreck my OS or something. I wonder if the SD card thing means they might eventually release a model with SD card support, if it's just a remnant of previous calculator OSes (since the Prizm OS and hardware (aside from the screen obviously) is very similar to the 128x64 monochrome FX-9860G, or if it's something else?
That's very cool, and an excellent question. If/when I get my Casio Prizm I will definitely disassemble it and look for possible vestigial SD card traces on the mainboard onto which I might be able to solder a socket, in case it was a proposed feature taken out for some reason. Good find.
KermMartian wrote:
DJ Omnimaga wrote:
It would be even funnier if the entire screen went blue with white text. ;D
That sounds like something that would be fun to code into an OS patch. Too bad (as far as I know) we have no idea how to do that yet.


Recompute an MD5 Hash and you probably can Razz

Sorry, necro'd while looking for something else.
No problem, I was hoping we could get this thread rolling again. It's actually good timing, because with the news that Snake_X uncovered about the Nspire CX not having any good programming features, brought here thanks to the excellent Souvik, I'm pretty much decided that I'm just going to get a Prizm for now, have fun coding and hacking it, and continue to not have any Nspire calculators until TI gets its act together. What do you guys think?
  
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