struct nffs_area_desc

struct nffs_area_desc {
    uint32_t nad_offset;    /* Flash offset of start of area. */
    uint32_t nad_length;    /* Size of area, in bytes. */
    uint8_t nad_flash_id;   /* Logical flash id */
};

Descriptor for a single nffs area. An area is a region of disk with the following properties:

1. An area can be fully erased without affecting any other areas.
2. Writing to one area does not restrict writes to other areas.

Regarding property 1: Generally, flash hardware divides its memory space into “blocks.” When erasing flash, entire blocks must be erased in a single operation; partial erases are not possible.

Regarding property 2: Furthermore, some flash hardware imposes a restriction with regards to writes: writes within a block must be strictly sequential. For example, if you wish to write to the first 16 bytes of a block, you must write bytes 1 through 15 before writing byte 16. This restriction only applies at the block level; writes to one block have no effect on what parts of other blocks can be written.

Thus, each area must comprise a discrete number of blocks.

An array of area descriptors is terminated by an entry with a nad_length value of 0.

Notes

Typically, a product's flash layout is exposed via its BSP-specific bsp_flash_dev() function. This function retrieves the layout of the specified flash device resident in the BSP. The result of this function can then be converted into the struct nffs_area_desc[] that nffs requires.

Header file

#include "nffs/nffs.h"