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→Wearleveling
=== Wearleveling ===
=== Wearleveling ===
The 3DS employs a wearleveling scheme on the savegame FLASH chips. This is done trough blockmaps. Depending on the size of the flashchip, these are located somewhere at the beginning of the flashchip, in the first sector. The structure is as follows:
The 3DS employs a wearleveling scheme on the savegame FLASH chips. This is done trough blockmaps and a journal. The blockmap is located at offset 0 of the flash chip, and is immediately followed by the journal. The initial state is dictated by the blockmap, and the journal is then applied to that.
The blockmap structure is simple:
<pre>
struct header_entry {
uint8_t chksums[8];
uint8_t phys_sec;
uint8_t alloc_cnt;
} __attribute__((__packed__));
</pre>
The journal structure is as follows:
<pre>
<pre>
struct sector_entry {
struct sector_entry {
uint8_t phys_sec; // Mapped from sector
uint8_t phys_sec; // Mapped from sector
uint8_t prev_phys_sec; // Virtual sector previously mapped to
uint8_t prev_phys_sec; // Virtual sector previously mapped to
uint8_t phys_realloc_cnt;// Amount of times physical sector has been remapped
uint8_t phys_realloc_cnt; // Amount of times physical sector has been remapped
uint8_t virt_realloc_cnt;// Amount of times virtual sector has been remapped
uint8_t virt_realloc_cnt; // Amount of times virtual sector has been remapped
uint8_t chksums[8];
uint8_t chksums[8];
} __attribute__((packed));
} __attribute__((__packed__));
struct long_sector_entry {
struct long_sector_entry{
struct sector_entry sector;
struct sector_entry sector;
struct sector_entry dupe;
struct sector_entry dupe;
uint32_t magic;
uint32_t magic;
};
}__attribute__((__packed__));
</pre>
</pre>