trezor-firmware/docs/storage/addon-block.md

Add-on Block

Fixed storage which stores an immutable binary-search tree of items. Each item consists of a pair of pointers to binary data of arbitrary length. These two pointers are interpreted as a key and a value. Since items contain only pointers, multiple instances of data are stored just once.

Block contains 3 logical parts: a) header (256 bytes) b) binary-search tree (variable size) c) item data (variable size)

Header

offset	length	name	description
0x0000	4	magic	magic TRAB
0x0004	64	sig	signature of the whole blob (except magic and sig)
0x0044	4	tree_count	number of elements in the tree
0x0048	4	items_size	length of the item section
0x004A	182	reserved	-

Binary-Search Tree

Each node of the tree has the following structure:

offset	length	name	description
...	2	key_offset	key offset (divided by 4)
...	2	value_offset	value offset (divided by 4)

Item Data

Each item has the following structure:

offset	length	name	description
...	2	item_len	item (key or value) length
...	2	item_flags	item (key or value) flags
...	item_len	item_data	item (key or value) data (padded to multiple of 4)