NAND Memory Layout

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Revision as of 20:37, 6 August 2007 by ExtendeD (talk | contribs) (When the TI-84+ are persisted)
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32MB are available in the flash memory used for storage. As in other TI calculator models with flash memory, it is used to store both the Operating System and what was called the "archive memory" on the previous models (this term loses its sense with the TI-Nspire as we'll see).

The TI-Nspire OS advertises 27.8MB of what it calls "storage capacity", which is the flash memory which can be filled with TI-Nspire documents. The storage capacity of the TI-Nspire CAS is 24.4MB. Saved documents are always stored in the storage memory. Documents being edited probably have a working copy in RAM, copied to the storage memory when the document is saved. In the ~4300KB left on the TI-Nspire, we find the OS image (3020KB for the .tno), and 1280KB of perhaps certificates, parts of the boot code which wouldn't be stored in the NOR flash (although 512KB seems more than enough for a boot code), and more... On the TI-NSspire CAS, ~7782KB are left for this. The OS image (.tnc) is 2577.5KB, which leaves 5204.5KB for the unknown part.

The Handheld Status dialog shows 5.7MB of "spaced used" on the TI-Nspire after a reset (i.e without any documents in memory), and 3.4MB on the TI-Nspire CAS. The system space of the TI-Nspire contains at least 1.57MB of archive memory + 24KB of RAM for the TI-84 Plus emulation, or even the whole ROM image (certificates, boot code, OS code and archive memory, 2MB + 24KB of RAM). This last option seems possible since the difference between the "spaced used" of the TI-NSpire and the TI-Nspire CAS is 2.3MB. We are not sure about the remaining 4.11MB/3.68MB. It is clear that the archive memory and the RAM of the TI-84 Plus is stored in flash memory at shutdown and not kept in RAM because they survive a keypad swap and battery replacement.

Since 32MB of RAM is available, which is quite a lot, we think the whole OS code is decrypted from the OS image and copied to RAM at boot time, when the message "Loading Operating System..." is displayed during ~8 seconds. The RAM is also used as temporary storage transparently for the user as described above. The file system compressed in the OS image may also be uncompressed to RAM at boot time when the message "Preparing file system, please wait..." is displayed during ~2 seconds to setup the OS file system. Since 2 seconds is quite fast, only part of the compressed files may be uncompressed (for example only the needed locale). For information the whole compressed file system (including the TI-84 Plus archive memory) is 2363.4KB once uncompressed.

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