Save data structure (Generation IV)
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The save data structure in the Nintendo DS is stored as a .SAV file, which is broken up into two pairs of blocks. Each pair has one small block, and one big block. The offsets for Platinum are different from Diamond and Pearl.
In Diamond and Pearl, the first small block starts at 0x00000 and ends at 0x0C0FF, the first big block starts at 0x0C100 and ends at 0x1E2DF. In Platinum, the first small block starts at 0x00000 and ends at 0x0CF2B, the first big block starts at 0x0CF2C and ends at 0x1F10F. The second pair of blocks are at the same address plus 0x40000 for all the three games.
One block pair is always a backup of the other block pair.
The last 0x14 bytes of each block (small and big) are used as a footer, with the following structure:
| Offset | Contents |
|---|---|
| 0x00-0x03 | Used to connect a small block with a big block |
| 0x04-0x07 | Number of the save |
| 0x08-0x0B | Size of the block |
| 0x0C-0x0F | K |
| 0x10-0x11 | T |
| 0x12-0x13 | Checksum of the block |
The game uses a CRC-16-CCITT algorithm for the checksums. These checksums are calculated from a whole block without taking the footer.
Example
SMALL BLOCK 1 D1 01 00 00 | 42 04 00 00 | 00 C1 00 00 | 23 06 06 20 | 00 00 | 7E 7A BIG BLOCK 1 D0 01 00 00 | F1 02 00 00 | E0 21 01 00 | 23 06 06 20 | 01 00 | 0D 39
SMALL BLOCK 2 D0 01 00 00 | 41 04 00 00 | 00 C1 00 00 | 23 06 06 20 | 00 00 | 0C 7F BIG BLOCK 2 D1 01 00 00 | F2 02 00 00 | E0 21 01 00 | 23 06 06 20 | 01 00 | F6 8A
Since the value of 0x0C0F0 - 0x0C0F3 is higher in small block 1 (42 04 00 00 > 41 04 00 00), that is the current small block. Then, by matching the value of 0x0C0EC - 0x0C0EF (which is D1 01 00 00) to the big block. This means that the current big block is actually big block 2 (assuming the big block's checksum is correct).
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