Within the nand-flash there exists at least three distinct areas:
- * the ipl
* the two fat filesystems flash0 and flash1
* the idstorage area
The keys are stored in an index which consists of two nand pages of 512 bytes. The index is identified by byte 6 of the spare area being 0x73. Byte 7 might be the id-storage version number. Byte 8 must be 1 (or possibly 0) and might indicate whether the storage is formatted or not, and a value greater than 1 in byte 9 indicates that the id-storage is read-only.
In my PSP with firmware 1.5, the id-storage index is identified by:
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0x56 0xa6 0x65 0x00 0xff 0xff 0x73 0x01 0x01 0x01 0xff 0xff 0x86 0xf1 0xff 0xffThe keys are stored in the corresponding user areas of the pages. Keys are 16-bit integers. The location of the data associated with a key is identified by the key's position in the index. For instance, a key appearing at position 97 (byte 194) in the index will find its associated data at location: 0xc0000 + (97 * 512) = 0xcc200.
Various subsystems in the PSP make use of the id-storage including usb, wlan, umd, etc.
The firmware provides a driver in idstorage.prx to facilitate manipulations.
Some common functions:
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/* sceIdStorageLookup() - Retrieves the value associated with a key
* args: key = id-storage key
* offset = offset within the 512-byte leaf
* buf = buffer with enough storage
* len = amount of data to retrieve (offset + len must be <= 512 bytes)
*/
int sceIdStorageLookup(u16 key, u32 offset, void *buf, u32 len);
/* sceIdStorageReadLeaf() - Retrieves the whole 512-byte container for the key
* args: key = id-storage key
* buf = buffer with at last 512-bytes of storage
*/
int sceIdStorageReadLeaf(u16 key, void *buf);
