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Messages - mikehill2003
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271
« on: March 24, 2011, 01:32:13 am »
Why does it have to be signed? (I've never understood the whole signing thing with apps)
If they are signed (I have no idea if they are) it would be to control who could make programs.
272
« on: March 23, 2011, 11:31:55 pm »
bump.
New Question: If I were to restore my iPod, and my last backup had a different OS, would it restore to that old OS?
If it's an iPod touch, then no. What OS are you on now, and what OS was your old OS? If the old one is relatively new, I can probably find a link. Also, is your iPod 1st, 2nd, 3rd, 3rd 8Gb, or 4th gen?
273
« on: March 23, 2011, 11:17:58 pm »
Yes, the two are signed with different keys. 
Actually, they are signed with the same key. The reason you cannot use a TI-Nspire CAS OS on the TI-Nspire or vice versa is because for an OS to validate:
- There must be an 8010 field present which matches the first two characters of the Product ID, which are stored in NAND flash (but don't bother trying to change it, because of the other protection described next)
- The 80E0 field must contain a byte matching a part of the value read from address 0x900A0028/0x900A002C (presumably, this is an 8 byte ROM inside the ASIC and cannot be changed)
Changing these fields in the OS image will mean the signature isn't valid and the OS won't load.
Fascinating. Is it boot1 or boot2 and/or the OS that does this?
274
« on: March 23, 2011, 10:10:55 pm »
So... boot1 might be changeable, boot2 is not. Flashing the NAND with Ndless is very unstable, and the reason has not yet been discovered. Do you think that the low success rate was due to some form of protection? Is it possible to see how the OS re-flashes the NAND, and possibly modify that routine if it checks the OS image signature?
Thanks for all the info! I really enjoy learning about systems like this.
The other way around. Although boot1 might be erasable, modifiable would be more difficult. And no, I don't think it's possible to see how the OS does it, or if it is, I don't think it's modifiable. It might be, though.
So the NAND can be changed, but the NOR cannot?
275
« on: March 23, 2011, 10:04:11 pm »
So... boot1 might be changeable, boot2 is not. Flashing the NAND with Ndless is very unstable, and the reason has not yet been discovered. Do you think that the low success rate was due to some form of protection? Is it possible to see how the OS re-flashes the NAND, and possibly modify that routine if it checks the OS image signature?
Thanks for all the info! I really enjoy learning about systems like this.
276
« on: March 23, 2011, 09:24:51 pm »
Yes, the two are signed with different keys. :(
Darn. Please pardon my ignorance, it will be a week or two before I get my Nspire basic (v2 with touchpad and ti-84 emu [I wanted an Nspire CAS, but this was nearly new and $60. A CAS would have cost twice as much.]). Are boot1 and boot2 stored on the same NAND flash rom? If so, is there any chance of using Ndless to flash an OS with an invalid signature and a boot2 to load it? Or would I need to re-flash the NAND directly? Soldering onto those tiny traces is tough (see attachment).
277
« on: March 23, 2011, 08:45:10 pm »
Can anyone tell me what the differences are (besides the obvious)? I assume TI provides two separate OS images, and something prevents the CAS OS from loading on the regular Nspire. Are they signed with two different keys?
278
« on: March 23, 2011, 06:42:48 pm »
Sorry to bump an old topic, but has there been any progress on adding CAS to the nspire basic?
279
« on: March 23, 2011, 05:43:36 pm »
Wow! Thanks for pointing that out bsl! Looking at the CAS+ and CAS boards side by side, there are some large differences between them. Now I really doubt that the CAS+ can run a production OS. Those aren't for the keyboard?
J02, probably...
But what's the purpose of the J04 present on older CAS+?
I can't really tell from that photo where the traces lead.
280
« on: March 23, 2011, 05:32:46 pm »
Those aren't for the keyboard?
281
« on: March 23, 2011, 05:22:00 pm »
282
« on: March 23, 2011, 05:04:59 pm »
Interesting. I've got several CAS+ so I can take the risk.
But I've only got an EPROM programmer
The NAND chip is a ST NAND256W3A.
Thanks, I'll try to find a datasheet. Okay, here is the xD card pinout http://pinouts.ru/Memory/xd_card_pinout.shtml
283
« on: March 23, 2011, 04:47:41 pm »
Unfortunately, as someone who enjoys taking things apart to learn how they work, I am still somewhat interested in the CAS+. Does anyone know if the OS is encrypted (on the NAND Flash)? Has anyone tried to directly dump the OS from it? If the CAS+ is anything like the released TI-Nspire/TI-Nspire CAS, then the OS is encrypted but the encryption key is present in the second-stage boot loader, which is merely compressed (and we can easily decompress it).
However, I don't think anybody has tried to dump the NAND flash by means of hardware hacking; I didn't know that was even feasible.
Well, I don't own an Nspire CAS(+ or not) yet, so I can't say for sure if it is feasible on an Nspire, but it has worked just fine for me on many other NAND Flash chips. ;D Give me a few minutes and I'll find a simple tutorial.This guy used an xD card reader. Simple ('cause xD cards are raw NAND in an expensive package) but it works pretty well. xD cards are pretty useful because you can use them to make a second, removable NAND. (Warning: Because the card reader contains the NAND controller chip, not all card readers work.) http://busydizzys.com/index.php/2010/12/24/reading-embedded-flash-chips-nand-tsop-without-removalSoldering this stuff is somewhat difficult. A microscope, steady hand, and hot glue really help.
284
« on: March 23, 2011, 02:59:57 pm »
Yes, significant work for trying to understand and reflash the CAS+ prototypes is currently underway, in another section of this forum and on the French-speaking TI-Bank forum. See, for example, http://ourl.ca/9688 
The prospect of reflashing CAS+ prototypes with the OS of commercial CAS models seems bleak, though.
Yeah, based on the info from that thread replacing the CAS+ OS with one signed with the production keys would be difficult. In my post I meant something a little more direct then the RS-232 USB Comm. I was referring to the NAND Flash-ROM.  Its been quite a while since I had to solder onto SMT stuff. Actually the Prizm does have a very long battery life. I've had my Prizm since Christmas now and I use it for at least one hour everyday. In that time I have not changed the batteries once.
Impressive. Is there a C compiler for it or is it ASM only?
285
« on: March 23, 2011, 01:33:27 pm »
Thanks for the warnings! I would get a Prizm, but I don't really care for the color screen (battery life is more important to me). Also, even though I don't use it very often, the CAS on my TI-89T and HP-50g is really nice. I would hate to buy a new calculator without CAS. ( I also have a Casio fx-9750GA+. Nice calc, but I rarely use it.)
Unfortunately, as someone who enjoys taking things apart to learn how they work, I am still somewhat interested in the CAS+. Does anyone know if the OS is encrypted (on the NAND Flash)? Has anyone tried to directly dump the OS from it?
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