Data groups

Principles

The first 1MB are divided into 8 data groups of 128kB each.

Data group #0 is not available (reserved for partition tables, certificates and secret keys, factory configuration etc).

Data group #1 stores the constants and technical flags.

Data group #2 stores the configuration.

Data group #3 stores the templates.

Data group #4 stores the statistics.

Data groups #4, #5, #6 and #7 are RFU.

Low-level implementation and wear-leveling

All the data groups are formatted and used the same way.

Every data group is made of 32 pages (each page is 4kB).

The pages are used by 2 : page 0 comes with page 16, page 1 with page 17, etc.

Data entries are distributed among the pages based on their low-order nibble:

  • entries #00, #10, #20 ... go to pages 0 and 16,
  • entries #01, #11, #21 ... go to pages 1 and 17, etc.

The flash is always accessed in 4-B blocks and aligned on 4-B boundaries.

The 1st block of every page stores the page's state:

  • 0xFFFFFFFF : the page is empty
  • 0xAA55FFFF : the page has room to receive new data
  • 0xAA55DEAD : the page contains valid data, and has no room left; in is being transferred to its sister page
  • any other value : error, the page shall be made empty again