NAND Memory Layout: Difference between revisions

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(Description of the CX NAND + incomplete description of the CM NAND)
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==NAND Flash==
NAND pages are 528-bytes long (512 + 16-bytes OOB area) on TI-Nspire and 2112-bytes long (2048 + 64-bytes OOB) on TI-Nspire CX/CM/CX II.


NAND pages are 528-bytes long (512 + 16-bytes header) on TI-Nspire and 2048-bytes long (2048 + 48-bytes header) on TI-Nspire CX/CM.
==Layout on Classic/CX/CM==


* pages 0000 to 001F (Nspire) or 0000 to 003F (CX/CM): written to /phoenix/manuf.dat at each boot
* pages 0000 to 001F (Nspire) or 0000 to 003F (CX/CM): written to /phoenix/manuf.dat at each boot.
** Offset 000-003: 3C B0 6E 79
** Offset 804-805: model ID (little-endian): 0C (Nspire CAS), 0D (Nspire Lab Cradle), 0E (Nspire), 0F (Nspire CX CAS), 10 (Nspire CX), 11 (Nspire CM CAS), 12 (Nspire CM)
** Offset 806-807: unknown - 00 00 or 10 00
** Offset 808-80F: optional default language (CX/CM), filled with FF if missing - ISO 639 supported language string padded with 00 (for exemple fr, en, ar, zh_CN for TI-Nspire CX-C or CM-C...)
** Offset 818-81B: signature - 91 5F 9E 4C (CX/CM)
** Offset 81C-81F: features (little-endian) - 0x05 (CM + CX Napoca), 0x85 (CX CR/HW-J+), 0x185 (CX CR4/HW-W+)
** Offset 820-823: default keypad - 4C 00 00 00 (CX/CM)
** Offset 824-825: lcd width - 40 01 (CX/CM)
** Offset 826-827: lcd height - F0 00 (CX/CM)
** Offset 228-229: lcd bpp - 10 00 (CX/CM)
** Offset 82A-82B: lcd color - 01 00 (CX/CM)
** Offset 82C-82F: offset diags - 00 00 32 00 (CX/CM)
** Offset 830-833: offset boot2 - 00 00 02 00 (CX/CM)
** Offset 834-837: offset boot data - 00 00 2C 00 (CX/CM)
** Offset 838-83B: offset file system - 00 00 40 00 (CX/CM)
** Offset 83C-83F: config clock - 02 10 56 00 (CX/CM)
** Offset 840-843: SDRAM config: 12 80 01 FC for 64MB (CX) or 11 80 01 FE for 32MB (CM)
*** Offset 840: SDRAM size in MB - keep 6 lowest bytes - size is 4*2^((value/8)+(value%8))
** Offset 844-847: lcd spi count - 02 00 00 00 (CX/CM)
** Offset 848-887: lcd spi data filled with 0xFF - 06 00 00 00 5C 00 00 00 30 00 00 00 04 00 00 00  (CX/CM)
** Offset 888-889: lcd light min - 1A 01 (CX/CM)
** Offset 88A-88B: lcd light max - CE 01 (CX/CM)
** Offset 88C-88D: lcd light default - 6A 01 (CX/CM)
** Offset 88E-88F: lcd light increment - 14 00 (CX/CM)
** Offset 890-893: 0C 01 A2 18 (CX/CM)
** Offset 894-923: display informations on the 12 elements of the splash screen (CX/CM): horizontal display offset + vertical display offset + width + height (2-bytes each) + data offset (4-bytes)
*** Offset 894-89F: Low Battery error icon [diplayed unknown]
*** Offset 8A0-8AB: Boot1 Recoverable Error icon [displayed 8th]
*** Offset 8AC-8B7: Send Diagnostics Software info icon [displayed 8th]
*** Offset 8B8-8C3: Boot2 Recoverable Error icon [displayed 8th]
*** Offset 8C4-8CF: Unrecoverable Error icon [displayed 8th]
*** Offset 8D0-8DB: Progress Bar Background [displayed 6th]
*** Offset 8DC-8E7: Progress Bar [displayed 7th]
*** Offset 8E8-8F3: permanent element #1 (background) [displayed 1st]
*** Offset 8F4-8FF: permanent element #2 (unused) [displayed 2nd]
*** Offset 900-90B: permanent element #3 (unused) [displayed 3th]
*** Offset 90C-917: permanent element #4 (unused) [displayed 4th]
*** Offset 918-923: permanent element #5 (unused) [displayed 5th]
** Offset 924-927: compressed splash screen data size
** Offset 928-92B: uncompressed splash screen data size (0x0000FA40 on CX EVT, 0x00029CD0 on all CX/CM)
** Offset 92C-92F: ? (0x00000756 on CX EVT, 0x000006D3 on all CX/CM)
** Offset 930-???: compressed splash screen data (same compression format as the boot2)
** Offset ???-???: TI-Certificate - fields present :
*** Production : 0x290 (0x100), 0x290 (0x100), 0x340 (0x1A4), 0x290 (0x100), 0x340 (0x115), 0x290 (0x100), 0xFFFF0 (0)
*** Development : 0x290 (0x100), 0x290 (0x100), 0x340 (0x1A4), 0x240 (0x80), 0x290 (0x100), 0x340 (0x115), 0x290 (0x100), 0xFFFF0 (0)
* pages 0020 to 0A7F (Nspire) or 0040 to 057F (CX/CM): boot2 image
* pages 0020 to 0A7F (Nspire) or 0040 to 057F (CX/CM): boot2 image
* pages 0A80 to 0AFF (Nspire) or 0580 to 063F (CX/CM): "bootdata" (every time this is modified, the next available page is used; if all 128 pages are in use, then the whole area is erased first)
* pages 0A80 to 0AFF (Nspire) or 0580 to 063F (CX/CM): "bootdata" (every time this is modified, the next available page is used; if all 128 pages are in use, then the whole area is erased first)
** Offset 00-03: Marker AA C6 8C 92
** Offset 00-03: Marker AA C6 8C 92
** Offset 04-07: Downgrade protection: minimum OS version allowed as a 4-bytes word (major-minor-lower1-lower2). Written during OS installation with the value found in the second field 8020 of the [[OS_upgrade_files#Structure OS upgrade file|OS upgrade file]]
** Offset 04-07: Downgrade protection: minimum OS version allowed as a 4-bytes word (major-minor-lower1-lower2). Written during OS installation with the value found in the second field 8020 of the [[OS_upgrade_files#Structure OS upgrade file|OS upgrade file]]
** Offset 08-0F: Seems to hold the press-to-test status (word, word, long word)
** Offset 08-0F: Hold the press-to-test status (word, word, long word)
***Offset 08-09: press to test mode
****00 : none
****01 : 84+ mode (OS is going to prompt for a 84+ keypad if not installed on next reboot)
****02 : fully restricted (all listed features disabled) - LED flashes in green
****03 : partially restricted (no or some listed features disables) - LED flashes in orange
****04 : old mode not used any more, for OS 1.x/2.x - at that time there were only 2 features which could be disabled - meant that one feature had been selected but not botg - LED flashes in green+orange
****06 : for Netherlands/Europe (since OS 4.3) - no programming, and easily disabled through any USB transfer - LED flashes in orange
***0A-0B : clear PTT folders content on next reboot (1 during the 1st reboot after (re)enabling PTT - default 0)
***0C-0D : disabled features in PTT mode - default 0
****Mode 3 :
*****bit 0 : geometry
*****bit 1 : drag&move in graphs
*****bit 2 : vectors
*****bit 3 : isPrime()
*****bit 4 : diff eq
*****bit 5 : ineq graphing
*****bit 6 : 3D graphing
*****bit 7 : rel/coniq graphing
*****bit 8 : trig
*****both bits 9+10 : logbase()
*****both bits 11+12 : poly and simult solving
****Mode 2 : all 13 previous bits are 1
****Mode 6 : all 13 previous bits are 0
***0E-0F : unkown - default 0 - sometimes 0x8000 in PTT mode
** Offset 10-13: If nonzero, BOOT1 will attempt to run DIAGS by default; if zero, it will skip straight to BOOT2. (Either behavior can be overridden with the Esc+Menu+G key combination.)
** Offset 10-13: If nonzero, BOOT1 will attempt to run DIAGS by default; if zero, it will skip straight to BOOT2. (Either behavior can be overridden with the Esc+Menu+G key combination.)
** Offset 14-1A: TI-84 Plus emulator 0A1 certificate field
** Offset 14-1A: TI-84 Plus emulator 0A1 certificate field
Line 14: Line 83:
** Offset 1F-61: TI-84 Plus emulator 0A2 certificate field
** Offset 1F-61: TI-84 Plus emulator 0A2 certificate field
** Offset 64-67: (OS 1.6+) Default LCD contrast (if not in range from 0x76 to 0x8A, assumed to be 0x80)
** Offset 64-67: (OS 1.6+) Default LCD contrast (if not in range from 0x76 to 0x8A, assumed to be 0x80)
* pages 0B00 to 0F7F (Nspire) or 0640 to 079F (CX): diags software
* pages 0B00 to 0F7F (Nspire) or 0640 to 079F (CX) or 0640 to 7BF (CM): diags software
* pages 0F80 to 0FFF (Nspire) or 07A0 to 07FF (CX): diags test results
* pages 0F80 to 0FFF (Nspire) or 0780 to 07FF (CX): diags test results
* pages from 1000 (Nspire) or 0800 (CX) or 07C0 (CM): factory images or filesystem
* pages from 1000 (Nspire) or 0800 (CX) or 07C0 (CM): factory images or filesystem


Line 29: Line 98:
If boot2 finds this header, the user is prompted to press 'I' on the keypad. After that, the image is copied to RAM before creating the filesystem (The filesystem also starts at page 0x1000, so it cannot co-exist with a factory image), and is installed the same as if it had been received from the serial port.
If boot2 finds this header, the user is prompted to press 'I' on the keypad. After that, the image is copied to RAM before creating the filesystem (The filesystem also starts at page 0x1000, so it cannot co-exist with a factory image), and is installed the same as if it had been received from the serial port.


==Misc notes==
==Layout on CX II==
32MB are available in the [[Hardware#Storage_.28.3F.29_memory|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 [[Hardware#Boot.2FKernel.28.3F.29_memory|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.
===Partitions===


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.
Partitions are aligned to erase block size (64 pages) and so the size and offsets in the table below are given in blocks.


Since 32MB of RAM is available, which is quite a lot, the whole OS code is decrypted from the [[OS_upgrade_files#TI-Nspire.img|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 OS is not stored in the file system, but separately in its own partition.
 
{| class="wikitable"
|-
  ! Name!! Size!! Offset
|-
  | Manuf || 1 || 0
|-
  | Bootloader || 4 || 1
|-
  | PTT Data || 1 || 5
|-
  | ??? || 1 || 6
|-
  | DevCert || 1 || 7
|-
  | OS Loader || 3 || 8
|-
  | Installer || 8 || 11
|-
  | Other Installer || 8 || 19
|-
  | OS Data (?) || 2 || 27
|-
  | Diags || 5 || 29
|-
  | ? || ? || ?
|-
  | OS file (weird header) || ? || 36
|-
  | Logging || 87 (?) || 114
|-
  | File System || ? || ?
|-
  | ? || ? || ?
|}
 
===Manuf Format===
 
The Manuf on CX II uses the same fields format as seen in [[OS upgrade files]].
 
: 5000 : Top-level field
:: 5100 - 2 : Product ID
:: 5200 - 2 : Unknown
:: 5300 - x : Language
:: 5400 - 4 : Hardware flags. Bit 0 is 1 if the "CapTIvate" touchpad is used.
:: 5500 - x : Optional: If present, the bootrom runs this as code
:: 5600 - 4 : Unknown
:: 57y0 - 4 : Unknown (repeats with different values for y)
:: 5500 - x : Contains pairs of addr/value to write
: 290 - 256 : 2048-bit Signature
: 290 - 256 : 2048-bit Signature (another one?)
: 340 - 420 : Public key (?)
:: 270 - 1: ?
:: 260 - 140: 1024-bit public key (?)
:: 2A0 - 270: 2048-bit public key (?)
: 340 - 277 : Public key (?)
:: 270 - 1: ?
:: 2A0 - 270: 2048-bit public key (?)
: 290 - 256: 2048-bit Signature (yet another one?)
: FFF0 - 0 : End
 
===Bootdata Format===
 
Like for previous versions, every time this is modified, the next available page is used. If all 128 pages are in use, the whole area is erased first.
 
: 000 - 003 : Signature: 44 41 54 41 ('D' 'A' 'T' 'A')
: 004 - 007 : Boot type (0 = OS Loader, 1 = Installer, 2 = Diags)
: 008 - 00B : Which installer to boot (0 = Installer, 1 = Other installer)
: 00C - 00F : Minimum OS version (little endian, e.g. 00 00 00 05)
: 010 - 01B : Unknown, filled with 00
: 01C - 3FF : Blank, filled with FF
: 400 - 7FF : Blank, filled with 00
:: 780 - 783 : Unknown, starts with 21

Latest revision as of 19:20, 24 September 2023

NAND pages are 528-bytes long (512 + 16-bytes OOB area) on TI-Nspire and 2112-bytes long (2048 + 64-bytes OOB) on TI-Nspire CX/CM/CX II.

Layout on Classic/CX/CM

  • pages 0000 to 001F (Nspire) or 0000 to 003F (CX/CM): written to /phoenix/manuf.dat at each boot.
    • Offset 000-003: 3C B0 6E 79
    • Offset 804-805: model ID (little-endian): 0C (Nspire CAS), 0D (Nspire Lab Cradle), 0E (Nspire), 0F (Nspire CX CAS), 10 (Nspire CX), 11 (Nspire CM CAS), 12 (Nspire CM)
    • Offset 806-807: unknown - 00 00 or 10 00
    • Offset 808-80F: optional default language (CX/CM), filled with FF if missing - ISO 639 supported language string padded with 00 (for exemple fr, en, ar, zh_CN for TI-Nspire CX-C or CM-C...)
    • Offset 818-81B: signature - 91 5F 9E 4C (CX/CM)
    • Offset 81C-81F: features (little-endian) - 0x05 (CM + CX Napoca), 0x85 (CX CR/HW-J+), 0x185 (CX CR4/HW-W+)
    • Offset 820-823: default keypad - 4C 00 00 00 (CX/CM)
    • Offset 824-825: lcd width - 40 01 (CX/CM)
    • Offset 826-827: lcd height - F0 00 (CX/CM)
    • Offset 228-229: lcd bpp - 10 00 (CX/CM)
    • Offset 82A-82B: lcd color - 01 00 (CX/CM)
    • Offset 82C-82F: offset diags - 00 00 32 00 (CX/CM)
    • Offset 830-833: offset boot2 - 00 00 02 00 (CX/CM)
    • Offset 834-837: offset boot data - 00 00 2C 00 (CX/CM)
    • Offset 838-83B: offset file system - 00 00 40 00 (CX/CM)
    • Offset 83C-83F: config clock - 02 10 56 00 (CX/CM)
    • Offset 840-843: SDRAM config: 12 80 01 FC for 64MB (CX) or 11 80 01 FE for 32MB (CM)
      • Offset 840: SDRAM size in MB - keep 6 lowest bytes - size is 4*2^((value/8)+(value%8))
    • Offset 844-847: lcd spi count - 02 00 00 00 (CX/CM)
    • Offset 848-887: lcd spi data filled with 0xFF - 06 00 00 00 5C 00 00 00 30 00 00 00 04 00 00 00 (CX/CM)
    • Offset 888-889: lcd light min - 1A 01 (CX/CM)
    • Offset 88A-88B: lcd light max - CE 01 (CX/CM)
    • Offset 88C-88D: lcd light default - 6A 01 (CX/CM)
    • Offset 88E-88F: lcd light increment - 14 00 (CX/CM)
    • Offset 890-893: 0C 01 A2 18 (CX/CM)
    • Offset 894-923: display informations on the 12 elements of the splash screen (CX/CM): horizontal display offset + vertical display offset + width + height (2-bytes each) + data offset (4-bytes)
      • Offset 894-89F: Low Battery error icon [diplayed unknown]
      • Offset 8A0-8AB: Boot1 Recoverable Error icon [displayed 8th]
      • Offset 8AC-8B7: Send Diagnostics Software info icon [displayed 8th]
      • Offset 8B8-8C3: Boot2 Recoverable Error icon [displayed 8th]
      • Offset 8C4-8CF: Unrecoverable Error icon [displayed 8th]
      • Offset 8D0-8DB: Progress Bar Background [displayed 6th]
      • Offset 8DC-8E7: Progress Bar [displayed 7th]
      • Offset 8E8-8F3: permanent element #1 (background) [displayed 1st]
      • Offset 8F4-8FF: permanent element #2 (unused) [displayed 2nd]
      • Offset 900-90B: permanent element #3 (unused) [displayed 3th]
      • Offset 90C-917: permanent element #4 (unused) [displayed 4th]
      • Offset 918-923: permanent element #5 (unused) [displayed 5th]
    • Offset 924-927: compressed splash screen data size
    • Offset 928-92B: uncompressed splash screen data size (0x0000FA40 on CX EVT, 0x00029CD0 on all CX/CM)
    • Offset 92C-92F: ? (0x00000756 on CX EVT, 0x000006D3 on all CX/CM)
    • Offset 930-???: compressed splash screen data (same compression format as the boot2)
    • Offset ???-???: TI-Certificate - fields present :
      • Production : 0x290 (0x100), 0x290 (0x100), 0x340 (0x1A4), 0x290 (0x100), 0x340 (0x115), 0x290 (0x100), 0xFFFF0 (0)
      • Development : 0x290 (0x100), 0x290 (0x100), 0x340 (0x1A4), 0x240 (0x80), 0x290 (0x100), 0x340 (0x115), 0x290 (0x100), 0xFFFF0 (0)
  • pages 0020 to 0A7F (Nspire) or 0040 to 057F (CX/CM): boot2 image
  • pages 0A80 to 0AFF (Nspire) or 0580 to 063F (CX/CM): "bootdata" (every time this is modified, the next available page is used; if all 128 pages are in use, then the whole area is erased first)
    • Offset 00-03: Marker AA C6 8C 92
    • Offset 04-07: Downgrade protection: minimum OS version allowed as a 4-bytes word (major-minor-lower1-lower2). Written during OS installation with the value found in the second field 8020 of the OS upgrade file
    • Offset 08-0F: Hold the press-to-test status (word, word, long word)
      • Offset 08-09: press to test mode
        • 00 : none
        • 01 : 84+ mode (OS is going to prompt for a 84+ keypad if not installed on next reboot)
        • 02 : fully restricted (all listed features disabled) - LED flashes in green
        • 03 : partially restricted (no or some listed features disables) - LED flashes in orange
        • 04 : old mode not used any more, for OS 1.x/2.x - at that time there were only 2 features which could be disabled - meant that one feature had been selected but not botg - LED flashes in green+orange
        • 06 : for Netherlands/Europe (since OS 4.3) - no programming, and easily disabled through any USB transfer - LED flashes in orange
      • 0A-0B : clear PTT folders content on next reboot (1 during the 1st reboot after (re)enabling PTT - default 0)
      • 0C-0D : disabled features in PTT mode - default 0
        • Mode 3 :
          • bit 0 : geometry
          • bit 1 : drag&move in graphs
          • bit 2 : vectors
          • bit 3 : isPrime()
          • bit 4 : diff eq
          • bit 5 : ineq graphing
          • bit 6 : 3D graphing
          • bit 7 : rel/coniq graphing
          • bit 8 : trig
          • both bits 9+10 : logbase()
          • both bits 11+12 : poly and simult solving
        • Mode 2 : all 13 previous bits are 1
        • Mode 6 : all 13 previous bits are 0
      • 0E-0F : unkown - default 0 - sometimes 0x8000 in PTT mode
    • Offset 10-13: If nonzero, BOOT1 will attempt to run DIAGS by default; if zero, it will skip straight to BOOT2. (Either behavior can be overridden with the Esc+Menu+G key combination.)
    • Offset 14-1A: TI-84 Plus emulator 0A1 certificate field
    • Offset 1B-1E: TI-84 Plus emulator 041 certificate field
    • Offset 1F-61: TI-84 Plus emulator 0A2 certificate field
    • Offset 64-67: (OS 1.6+) Default LCD contrast (if not in range from 0x76 to 0x8A, assumed to be 0x80)
  • pages 0B00 to 0F7F (Nspire) or 0640 to 079F (CX) or 0640 to 7BF (CM): diags software
  • pages 0F80 to 0FFF (Nspire) or 0780 to 07FF (CX): diags test results
  • pages from 1000 (Nspire) or 0800 (CX) or 07C0 (CM): factory images or filesystem

Factory images

At startup, boot2 checks the NAND flash for a pre-loaded factory image. The format is a 32-byte header followed by the .tnc/.tno file contents:

  • Offset 00-13: String "***PRELOAD_IMAGE***"
  • Offset 14-17: 55 F0 01 55
  • Offset 18-1B: (unknown)
  • Offset 1C-1F: Size of image (in big-endian)

If boot2 finds this header, the user is prompted to press 'I' on the keypad. After that, the image is copied to RAM before creating the filesystem (The filesystem also starts at page 0x1000, so it cannot co-exist with a factory image), and is installed the same as if it had been received from the serial port.

Layout on CX II

Partitions

Partitions are aligned to erase block size (64 pages) and so the size and offsets in the table below are given in blocks.

The OS is not stored in the file system, but separately in its own partition.

Name Size Offset
Manuf 1 0
Bootloader 4 1
PTT Data 1 5
??? 1 6
DevCert 1 7
OS Loader 3 8
Installer 8 11
Other Installer 8 19
OS Data (?) 2 27
Diags 5 29
? ? ?
OS file (weird header) ? 36
Logging 87 (?) 114
File System ? ?
? ? ?

Manuf Format

The Manuf on CX II uses the same fields format as seen in OS upgrade files.

5000 : Top-level field
5100 - 2 : Product ID
5200 - 2 : Unknown
5300 - x : Language
5400 - 4 : Hardware flags. Bit 0 is 1 if the "CapTIvate" touchpad is used.
5500 - x : Optional: If present, the bootrom runs this as code
5600 - 4 : Unknown
57y0 - 4 : Unknown (repeats with different values for y)
5500 - x : Contains pairs of addr/value to write
290 - 256 : 2048-bit Signature
290 - 256 : 2048-bit Signature (another one?)
340 - 420 : Public key (?)
270 - 1: ?
260 - 140: 1024-bit public key (?)
2A0 - 270: 2048-bit public key (?)
340 - 277 : Public key (?)
270 - 1: ?
2A0 - 270: 2048-bit public key (?)
290 - 256: 2048-bit Signature (yet another one?)
FFF0 - 0 : End

Bootdata Format

Like for previous versions, every time this is modified, the next available page is used. If all 128 pages are in use, the whole area is erased first.

000 - 003 : Signature: 44 41 54 41 ('D' 'A' 'T' 'A')
004 - 007 : Boot type (0 = OS Loader, 1 = Installer, 2 = Diags)
008 - 00B : Which installer to boot (0 = Installer, 1 = Other installer)
00C - 00F : Minimum OS version (little endian, e.g. 00 00 00 05)
010 - 01B : Unknown, filled with 00
01C - 3FF : Blank, filled with FF
400 - 7FF : Blank, filled with 00
780 - 783 : Unknown, starts with 21
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